2018 Max-Born-Institut Für Nichtlineare Optik Und Kurzzeitspektroskopie Im Forschungsverbund Berlin E.V

Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie im Forschungsverbund Berlin e.V.

Annual Report 2018 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie im Forschungsverbund Berlin e.V.

Annual Report 2018

Annual Report 2010 Annual Report 2018

Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie im Forschungsverbund Berlin e.V.

Max-Born-Straße 2 A 12489 Berlin Germany Phone: (++49 30) 63 92 - 15 05 Fax: (++49 30) 63 92 - 15 19 [email protected] www.mbi-berlin.de

2 Preface 5

Scientific Highlights

Development of the first lens for extreme-ultraviolet light 11 Looking at molecules from two sides with table-top femtosecond soft-X-rays 13 Instant x-ray footprints 15 OPCPA development at MBI 16 High harmonic spectroscopy of the Mott phase transition in a strongly correlated solid 19 Laser-driven electron recollision remembers molecular orbital structure 20 Magnetic nanostructures in ferrimagnets: fast and small 21 Electric polarization in the macroscopic world and electrons moving at atomic scales – 23 a new link from femtosecond x-ray experiments Photoexcitation circular dichroism in chiral molecules 25

Short Description of Research Projects

1 – Laser Research 1.1: Fundamentals of Extreme Photonics 29 1.2: Ultrafast Laser Physics and Nonlinear Optics 37

2 – Ultrafast and Nonlinear Phenomena: Atoms, Molecules, and Clusters 2.1: Time-resolved XUV-science 47 2.2: Strong-field Few-body Physics 54

3 – Ultrafast and Nonlinear Phenomena: Condensed Phase 3.1: Dynamics of Condensed Phase Molecular Systems 64 3.2: Solids and Nanostructures: Electrons, Spins, and Phonons 70 3.3: Transient Structures and Imaging with X-rays 78

4 – Laser Infrastructure and Knowledge Transfer 4.1: Implementation of Lasers and Measuring Techniques 82 4.2: Application Laboratories and Technology Transfer 88 Femtosecond Application Laboratories (FAL) 88 NanoMovie – Application Laboratory for nanoscopic spectroscopy and imaging 89 Berlin Laboratory for innovative X-ray Technologies (BLiX) 92 4.3: Nanoscale Samples and Optics 95

Appendices

Appendix 1: Publications 100 Appendix 2: External Talks, Teaching 112 Appendix 3: Ongoing Bachelor, Master, and PhD theses 119 Appendix 4: Guest Lectures at the MBI 121 Appendix 5: Grants and Contracts 123 Appendix 6: Activities in Scientific Organizations 124

3 4 Preface

This Annual Report provides an overview of the research activities and results of the Max-Born- Institute (MBI) in 2018. A presentation of selected scientific highlights is followed by reports on all projects which are part of the scientific program of the institute. A complete record of publications and invited talks is given in the appendix, together with information on academic teaching and training, guest lectures, activities in scientific organizations, and third-party funding. More detailed information is available on the MBI website (http://www.mbi-berlin.de).

In 2018, a number of key results stand out in the strong scientific output of MBI:

• Refractive optical elements play an essential role in numerous applications ranging from per- sonal eyecare to microscopy, however, until recently, no such optical elements existed in the extreme ultra-violet (XUV) wavelength range. In recent experiments at the MBI, it was demonstrated that high density atomic or molecular gasjets can be used as refractive optical elements that are able to deflect or focus XUV radiation. Building on these results it may be possible in future to develop XUV lenses with time-dependent focal properties, or lenses that are able to focus attosecond laser pulses.

• For the first time, near edge x-ray absorption spectra of organic molecules in solution were measured with a high harmonic generation source. Combining a HHG source covering the photon energy range up to 450 eV with a liquid flatjet allowing for transmission experiments, spectra could be simultaneously acquired at both the carbon and nitrogen edge. This approach opens new perspectives for the study of ultrafast rearrangements of solution phase molecular systems, allowing for simultaneous time-resolved probing of different atomic sites in future experiments.

• While free-electron x-ray lasers generate a sufficient number of photons in a coherence volume to allow for non-linear x-ray matter interaction, the study and use of these effects is often ham- pered by the lack of knowledge of the actual fluence distribution on the sample on a shot-by-shot basis. MBI scientists have developed an approach allowing to record a spatial map of the fluence distribution on a solid sample together with the diffraction pattern generated by the very same free electron laser shot, allowing for quantitative fluence-dependent experiments at fluctuating x-ray sources. As a byproduct, the approach allows for easy real-time adjustment of the x-ray optics and sample position.

• The MBI projects on optical parametric chirped pulse amplification (OPCPA) have lead to a number of ultrafast light sources with unprecedented performance parameters. A system working at a 100 kHz repetition rate produces 190 μJ, 7 fs, CEP-stable pulses at 800 nm and now drives a high repetition rate attosecond pump-probe beam line. A second OPCPA system operating at 100 kHz provides 1.55 µm signal and 3.1 μm idler pulses of a sub-100 fs duration with average powers up to several tens of watts. A midwave-infrared OPCPA system operating at 1 kHz generates 80 fs, 3.5 mJ pulses, translating into a peak power of several tens of GW, which represents a new peak performance level at this wavelength. This system now serves as a driver for a copper Kα hard x-ray source.

• Traditionally, phase transitions have been viewed as a discontinuity in a state of an infinitely large system at its equilibrium. This perspective has now changed with the advent of dynamical quantum phase transitions in finite systems, shaken out of their equilibrium. The work of the MBI team shows how highly nonlinear optical response, high harmonic generation, can be used to time-resolve a light-induced phase transition in a canonical strongly correlated system, the Fermi-Hubbard lattice. The time resolution can be as good as a femtosecond, far better than a single cycle of the light electric field triggering the phase transition. Thus, high harmonic generation offers a practical tool for achieving the elusive goal of resolving phase transition in quantum systems.

• Fundamental understanding of the process of laser-driven ion-electron recollision has led to the emergence of the field of attosecond science and novel spectroscopies that are based on the diffraction of laser-generated photoelectrons. Challenging common theoretical descriptions of the recollision process, experiments have been performed demonstrating that the recollision process is strongly influenced by the nature of the orbital from which the recolliding electron was

5 originally removed (by strong field ionization). This work has important implications for the proper analysis of laser-induced electron diffraction (LIED) experiments.

• Using x-ray spectro-holography, chiral magnetic skyrmions with a diameter as small as 10 nm could be observed in ferrimagnetic Gd44Co65 thin films at room temperature. In the same material, spin-orbit torques administered via current pulses in an adjacent platinum layer were demonstrated to drive chiral domain walls with speeds exceeding 1000 m/s, making the tiny skyrmion spin textures interesting as representations of single bits in novel magnetic data storage concepts.

• Femtosecond x-ray powder diffraction, a technique pioneered by MBI, gives insight in transient electron distributions at atomic length and time scales. A combined experimental and theoretical approach now establishes a direct quantitative connection between time-dependent microscopic charge densities and macroscopic electric polarizations, thus extending the existing adiabatic quantum phase methods towards ultrafast polarization dynamics. The new concept was demonstrated with the prototype ferroelectric ammonium sulfate where a picosecond switching of the full electric polarization by coherent phonon excitations was observed. This behavior holds strong potential for device applications.

• Chiral molecules are important in our life, hence, identifying and separating chiral molecules with optical means is an important, but challenging goal. While circularly polarized light constitutes a helix – i.e. a basic chiral structure – in space, the pitch of this helix is typically much larger than many molecules, leading to a small enantio-sensitive response. In an international collaboration, MBI researchers have demonstrated how using an ultrashort light pulse offers a new and very sensitive method to probe chirality. Such short pulses excite electrons in molecules into a twisting motion, the direction of which reveals the molecules' handedness. In contrast to the light helix, here the chiral motion is excited by the molecule itself, which has just the right size to do it. The conversion of electronic ring currents coherently induced by an ultrashort laser pulse into an enantio-sensitive helical current can be close to 100 %. The work also identifies fundamental quantities that control the efficiency of such conversion, and demonstrates how these currents can be probed and time-resolved.

More than 170 scientific articles have been published in peer-reviewed journals and books, including a substantial number of papers in a wide range of high-impact journals. The number of invited talks at international conferences has been maintained at a high level.

In 2018, several of our junior researchers received calls for faculty positions: Daniela Rupp accepted a position as Assistant Professor at the ETH Zürich, Switzerland, Tianli Feng has accepted a position as an Associate Professor at Shandong University, China, while Bastian Pfau has declined an offer of a Junior Professorship at Siegen University, Germany. Within the theory department of MBI, a new group led by Sangeeta Sharma has started its work towards the end of the year, focusing on condensed matter theory.

There have been several academic honors and recognitions for MBI scientists and staff members. Eric Nibbering received an ERC Advanced Grant to investigate the elementary steps of aqueous proton transfer dynamics between acids and bases. Both leaders of the two MBI junior research groups were awarded for their research. Benjamin Fingerhut, leading an Emmy Noether junior group at MBI, received an ERC Starting Grant for his theoretical work addressing ultrafast biomolecular dynamics via a non-adiabatic approach. Daniela Rupp, leader of a junior group on ultrafast dynamics in nanoplasma, was awarded the Karl-Scheel-Award from the Berlin Chapter of the German Physical Society. Furthermore, she received the Young Talent Award handed out by the Mayor of Berlin in connection with the annual Science Award of the Governing Mayor of Berlin. For his PhD thesis work on the generation of intense mid-infrared laser pulses, Lorenz von Grafenstein was honored with the Carl-Ramsauer-Award by the Berlin Chapter of the German Physical Society. Thomas Elsaesser was elected as the Secretary of the Class of Mathematics and Natural Sciences of the Berlin-Branden- burg Academy of Science and Humanities.

We would like to thank our staff members, guest scientists, and collaboration partners for their enthu- siasm and dedicated research work and, last but not least, our funding bodies for their support of MBI.

Berlin, March 2019

Stefan Eisebitt Thomas Elsaesser Marc Vrakking

6 Research Structure of the Max-Born-Institut

1 – Laser Research

1.1 1.2 Fundamentals of Ultrafast Laser Physics Extreme Photonics and Nonlinear Optics

2 – Ultrafast and Nonlinear Phenomena: 3 – Ultrafast and Nonlinear Phenomena: Atoms, Molecules, and Clusters Condensed Phase

2.1 3.1 Time-resolved XUV-science Dynamics of Condensed Phase Molecular Systems 2.2 3.2 Strong-field Few-body Physics Solids and Nanostructures: Electrons, Spins, and Phonons 3.3 Transient Structures and Imaging with X-rays

4 – Laser Infrastructure and Knowledge Transfer

4.1 4.2 4.3 Implementation of Lasers Application Laboratories Nanoscale Samples and Measuring Techniques and Technology Transfer and Optics

Organizational Structure of the Max-Born-Institut

Board of Trustees of the Forschungsverbund Berlin e.V.

FVB Managing Director Board of Directors Scientific Advisory Board

Executive Assistant

Division A: Division B: Division C: Attosecond Physics Transient Electronic Structure Nonlinear Processes in and Nanoscience Condensed Matter A1: Strong-field Processes at B1: Electron and Spin Dynamics C1: Femtosecond Spectroscopy of Extreme Wavelengths Molecular Systems

A2: Ultrafast XUV-Physics B2: Imaging and Coherent X-rays C2: Solid State Light Sources

A3: Ultrafast Lasers and B3: Laser Development C3: Femtosecond Spectroscopy Nonlinear Optics of Solids

Junior Group: Ultrafast Dynamics in Nanoplasma

Theory Department Attosecond Theory Strong-field Theory Theoretical Optics & Photonics

Condensed Matter Theory Junior Group: Biomolecular Dynamics

Administration IT Maintenance Library Mechanical Design and Workshop

7 Members of the Scientific Advisory Board

Prof. Dr. Giulio Cerullo Politecnico de Milano, Dipartimento di Fisica, Italy

Prof. Dr. Majed Chergui École Polytechnique Fédérale de Lausanne (EPFL), Institute of Chemical Sciences and Engineering, Switzerland

Prof. Tony Heinz Stanford University, Department of Applied Physics, USA

Prof. Dr. Franz X. Kaertner (Chair) DESY Hamburg, Center for Free-Electron Laser Science (CFEL) & Universität Hamburg, Fachbereich Physik, Germany

Prof. Dr. Jon Marangos Imperial College London, Department of Physics, UK

Prof. Dr. Didier Normand (until March 31, 2018) IRAMIS, Institut Rayonnement Matière de Saclay, France

Prof. Dr. Christoph Quitmann Lund University, Max IV Laboratory, Sweden

Prof. Dr. Ursula Roethlisberger École Polytechnique Fédérale de Lausanne (EPFL), Institute of Chemical Sciences and Engineering, Switzerland

Prof. Dr. Jan Michael Rost Max-Planck-Institut für Physik komplexer Systeme, Dresden, Germany

Representatives of the Cooperating Universities

Prof. Dr. Oliver Benson Humboldt-Universtität zu Berlin, Institut für Physik, Germany

Prof. Dr. Ulrike Woggon (until May 31, 2018) Technische Universität Berlin, Institut für Optik und Atomare Physik, Germany

Prof. Dr. Andreas Knorr (from July 1, 2018) Technische Universität Berlin, Institut für Optik und Atomare Physik, Germany

Prof. Dr. Felix von Oppen Freie Universität Berlin, Fachbereich Physik, Germany

Representatives of the Federal Republic and the State of Berlin

Dr. Frank Wolf Bundesministerium für Bildung und Forschung, Ref. 711, Bonn, Germany

Dr. Björn Maul Senatskanzlei, Wirtschaft und Forschung, Ref. VI D, Berlin, Germany

MBI is a member of the Leibniz Association

8 Scientific Highlights

9 10 Development of the first lens for extreme-ultraviolet light

L. Drescher, O. Kornilov, T. Witting, G. Reitsma, N. Monserud, A. Rouzée, J. Mikosch, M. J. J. Vrakking, and B. Schütte

A first refractive lens was developed that focuses ex- tosecond durations (1 as = 10-18 s). However, in spite treme ultraviolet beams. Instead of using glass, which of the large number of XUV sources and applications, is non-transparent in the extreme-ultraviolet region, the no XUV lenses have existed up to now. The reason is lens was formed by a jet of atoms. The results provide that XUV radiation is strongly absorbed by any solid novel opportunities for the imaging of biological sam- or liquid material and thus simply cannot pass through ples on the shortest timescales. conventional lenses.

A tree trunk partly submerged in water appears to be In order to focus XUV beams, a different approach was bent. Since hundreds of years, people know that this is therefore taken: a lens was formed by a jet of atoms of caused by refraction, i.e. the fact that light changes its a noble gas, helium (see Fig. 1). This lens benefits from direction when traveling from one medium (water) to an- the high transmission of helium in the XUV spectral other (air) at an angle. Refraction is also the underlying range and at the same time can be precisely controlled physical principle behind lenses, which play an indis- by changing the density of the gas in the jet. This is pensable role in everyday life: They are a part of the hu- important in order to tune the focal length and minimize man eye, and they are used as glasses, contact lenses, the spot sizes of the focused XUV beams. as camera objectives and for controlling laser beams. The operation of the lens relies on the existence of Following the discovery of new regions of the electro- absorption resonances in the helium gas. Just below magnetic spectrum such as ultraviolet (UV) and X-ray each resonance, the refractive index takes on a diverg- radiation, refractive lenses were developed that are ing positive value, whereas just above each resonance specifically adapted to these spectral regions. Elec- its value is negative and strongly decreasing. By as- tromagnetic radiation in the extreme-ultraviolet (XUV) sembling a high density of helium gas in a properly region is, however, somewhat special. It occupies the shaped volume, an object with a desirable refractive wavelength range between the UV and X-ray domains, index profile can be created. Indeed, by carefully tai- but unlike the two latter types of radiation, it can only loring the shape and density of the helium gas medi- travel in vacuum or strongly rarefied gases. Nowadays um, optical components such as lenses or prisms can XUV beams are widely used in semiconductor lithog- be constructed that focus or bend the incoming XUV raphy as well as in fundamental research, where they radiation. are employed to understand and control the structure and dynamics of matter. They enable the generation of Compared to curved mirrors that are often used to focus the shortest human-made light pulses, which reach at- XUV radiation, gaseous refractive lenses have a num-

Credit: O. Kornilov/L. Drescher

Fig. 1: Focusing of an XUV beam by a jet of atoms that is used as a lens.

11 Fig. 2: Invisible rainbow that is generated by a jet of helium atoms. Light with ‘colors’ close to resonances of helium are either defl ected upwards or downwards.

ber of advantages: A ‘new’ lens is constantly generated through the fl ow of atoms in the jet, meaning that problems with laser-induced damage are avoided. Fur- thermore, as was shown, a gas lens results in virtually no loss of XUV radiation. This is in stark contrast with refl ective XUV optical components, which typically incur losses of at least several tens of percent. Such losses are highly undesirable, because the generation of XUV radiation is complex and often very expensive.

Besides reporting the operation of a gaseous lens, the reported work furthermore demonstrated that an atomic jet can act as a prism separating the XUV radiation into its constituent spectral components (see Fig. 2). This can be compared to the observation of a rainbow, resulting from the breaking of the sun light into its spectral colors by water droplets, except that the ‘colors’ of the XUV light are not visible to the human eye.

The development of gas-phase lenses and prisms makes it possible to transfer optical techniques that are based on refraction and that are widely used in the visible and infrared part of the electromagnetic spectrum, to the XUV spectral domain. Gaseous lenses could e.g. be exploited to develop an XUV microscope or to focus XUV beams to nanometer spot sizes. This may be applied in the future, for instance, to observe structural changes of biomolecules on the shortest timescales.

Publication

DKW18: L. Drescher, O. Kornilov, T. Witting, G. Reitsma, N. Monserud, A. Rouzée, J. Mikosch, M. J. J. Vrakking, and B. Schütte; Extreme-ultraviolet refractive optics; Nature 564 (2018) 91–94

12 Looking at molecules from two sides with table-top femtosecond soft-X-rays

C. Kleine, M. Ekimova, G. Goldsztejn, S. Raabe, C. Strüber, J. Ludwig, S. Yarlagadda, S. Eisebitt, M. J. J. Vrakking, T. Elsaesser, E. T. J. Nibbering, and A. Rouzée

X-ray spectroscopy provides direct access into the electronic nature of chemical bonds, from which the outcome of chemical reactions can be understood. In- 1 tense activities are currently pursued at a large num- 0.8 ber of laboratories to develop new x-ray sources and 0.6 to implement novel measurement methods to explore 0.8 the structural aspects of ultrafast photoinduced chem- 0.4 270 280 290 ical reactions. We have now successfully combined a 0.6 table-top laser-based extreme high-order harmonic source for short-pulse soft-x-ray absorption spectroscopy in the water window [1] with novel fl atjet technology 0.4 [2]. By doing so, we provide the fi rst demonstration of simultaneous probing of carbon and nitrogen atoms in Normalized Intensity organic molecules in aqueous solution using a table-top 0.2 soft X-ray source.

0 X-ray absorption spectroscopy (XAS) monitors unoccu- 300 350 400 450 pied electronic orbitals with element, oxidation-state and Photon nergy [eV] spin specifi city, from which the electronic structure can be derived. For the majority of organic molecules the soft-X-ray spectral region (100-1000 eV) is relevant, as Fig. 1: the K-edge transitions of low-Z elements (C, N, and O), High harmonics spectrum recorded with the soft and the L-edges of 3d metals are located in this spectral X-ray spectrometer. In the inset, we show an expand- range [3,4]. XAS is typically performed at large scale ed view of the harmonic spectrum below 300 eV. The facilities, such as storage rings or free-electron lasers. dip observed in the spectrum near 280 eV is due to Table-top laser-based sources have until now only been contamination of the X-ray optics by carbon-contain- sparsely used to probe pure materials, e.g., metals and ing compounds. organic fi lms [5,6]. So far, measurements of the carbon

0.4 Fig. 2: (a) (b) 0.16 Absorbance of (a) O=C(NH2)2, (c) 0.3 O=C(NH2)2 0.12 CaCl2, and (e) NaNO3 (black solid lines) recorded with our table-top 0.2 0.08 XAS setup shown together with 0.1 0.04 their corresponding confi dence intervals (grey areas). The absor- 0 0 300 340 380 420 290 310 410 420 bance of the pure water solvent 0.8 CaCL2 (c) (d) is displayed as dashed lines. The 0.4 XAS measurements obtained at the 0.6 0.3 UE52_SGM beamline at BESSY II 0.4 0.2 near the C K−edge (blue) and N K− 0.2 0.1 edge (orange) are shown in panels

Absorbance [OD] Absorbance [OD] a and e. Panels b, d, and f show a 0 0 Absorbance [OD] 300 340 380 420 340 350 360 zoom near the C and N K-edges, or (e) (f) Ca L3,L2-edges for the three sam- 0.3 0.16 ples, corrected for the absorption NaNO3 0.12 from the pure solvent. Here, the 0.2 spectra taken at BESSY II (blue 0.08 0.1 dashed and orange dashed lines) 0.04 have been convoluted with a spec- 0 0 tral broadening function to match 300 340 380 420 400 410 420 the resolution of the table-top HHG Photon Energy [eV] setup.

13 extending up to 450 eV (Figure 1). We have combined this source with liquid fl atjet technology fully function- ing under vacuum conditions. Steady-state absorption spectra of organic molecules and inorganic salts in a thin (~ 1 µm) sheet of aqueous solution can now be measured, throughout the so-called water window region between 200-540 eV (Figure 2). In particular, this technique enables the simultaneous local probing at both carbon and nitrogen sites within the molecules. With this we demonstrate the feasibility of simultaneously following multiple sites within molecular systems (cover fi g- ure), with the potential of probing possible correlations between these sites upon molecular rearrangements.

This investigation represents a major step towards the systematic investigation of ultrafast rearrangements of solution phase molecular systems with femtosecond soft X-ray spectroscopy. New insights into ultrafast charge transport processes and photo-induced reactions in chem- Fig. 3: istry and biology are envisaged to become accessible. Liquid fl atjet (solvated urea) illuminated by a broadband soft X-ray pulse obtained by high-order harmonic generation. The insets show the steady-state absorption of urea at the C and N K-edges extracted from the Publication in press measurements. KEG: C. Kleine, M. Ekimova, G. Goldsztejn, S. Raabe, C. Strüber, J. Ludwig, S. Yarlagadda, S. Eisebitt, M. J. X-ray spectroscopy provides direct access into the J. Vrakking, T. Elsaesser, E. T. J. Nibbering, and A. Rou- electronic nature of chemical bonds, from which the zée: Soft X-ray Absorption Spectroscopy of Aqueous outcome of chemical reactions can be understood. In- Solutions Using a Table-Top Femtosecond Soft X-ray tense activities are currently pursued at a large num- Source, J. Phys. Chem. Lett. ber of laboratories to develop new x-ray sources and to implement novel measurement methods to explore the structural aspects of ultrafast photoinduced chemical reactions. We have now successfully combined a References table-top laser-based extreme high-order harmonic source for short-pulse soft-x-ray absorption spectrosco- [1] T. Popmintchev, M.-C. Chen, D. Popmintchev, P. py in the water window [1] with novel fl atjet technology Arpin, S. Brown, S. Ališauskas, G. Andriukaitis, T. Balči- [2]. By doing so, we provide the fi rst demonstration of unas, O. D. Mücke, A. Pugzlys, A. Baltuška, B. Shim, simultaneous probing of carbon and nitrogen atoms in S. E. Schrauth, A. Gaeta, C. Hernández-García, L. Pla- organic molecules in aqueous solution using a table-top ja, A. Becker, A. Jaron-Becker, M. M. Murnane, H. C. soft X-ray source (Figure 3). Kapteyn; Science 336 (2012) 1287-1291

X-ray absorption spectroscopy (XAS) monitors unoccu- [2] M. Ekimova, W. Quevedo, M. Faubel, Ph. Wernet, pied electronic orbitals with element, oxidation-state and and E. T. J. Nibbering; Struct. Dyn. 2 (2015) 054301 spin specifi city, from which the electronic structure can be derived. For the majority of organic molecules the soft-X-ray spectral region (100-1000 eV) is relevant, as [3] J. Stöhr, NEXAFS Spectroscopy, Springer Ser. Sur- the K-edge transitions of low-Z elements (C, N, and O), face Sci. Vol. 25 (Springer, Berlin, 1992) and the L-edges of 3d metals are located in this spectral range [3,4]. XAS is typically performed at large scale [4] J. W. Smith, and R. J. Saykally, Chem. Rev. 117 facilities, such as storage rings or free-electron lasers. (2017) 13909−13934 Table-top laser-based sources have until now only been sparsely used to probe pure materials, e.g., metals and [5] S. L. Cousin, F. Silva, S. Teichmann, M. Hemmer, B. organic fi lms [5,6]. So far, measurements of the carbon Buades, and J. Biegert, Opt. Lett. 39 (2014) 5383-5386 or nitrogen K-edges of organic molecules in dilute aqueous solution using the latter approach have not been [6] D. Popmintchev, B. R. Galloway, M.-C. Chen, F. Dol- reported. lar, C. A. Mancuso, A. Hankla, L. Miaja-Avila, G. O’Neil, J. M. Shaw, G. Fan, S. Ališauskas, G. Andriukaitis, T. We have now developed a bright source of femtosecond Balčiunas, O. D. Mücke, A. Pugzlys, A. Baltuška, H. C. soft X-ray pulses, making use of the extreme high-or- Kapteyn, T. Popmintchev, and M. M. Murnane, Phys. der harmonic generation process. Long-wavelength Rev. Lett. 120 (2018) 093002 (1.8 µm) driver pulses generated with an amplifi ed Ti:sapphire laser system were used to generate high-order harmonics well above the conventional spectral range, now

14 Instant x-ray footprints

M. Schneider1, C. M. Günther1,2, B. Pfau1, F. Capotondi3, M. Manfredda3, M. Zangrando3,4, N. Mahne3,4, L. Raimondi3, E. Pedersoli3, D. Naumenko3, and S. Eisebitt1,2 1Max-Born-Institut, Berlin, Germany, 2Technische Universität Berlin, Berlin, Germany, 3Elettra Sincrotrone Trieste S.C.p.A., Basovizza, Italy, 4Istituto Officina dei Materiali, Consiglio Nazionale delle Ricerche, Basovizza, Italy

Free-electron lasers (FELs) deliver intense and coherent x-ray pulses – a prerequisite to investigate and ex- 0 ploit non-linear processes in the interaction of x-rays 10 with matter. Analogous to the development of non-linear optics after the invention of lasers in the optical regime, 10-1 the application of these processes is expected to have a widespread impact on numerous research fi elds. A pivotal parameter in this context is the fl uence of the radiation 10-2 incident on the sample during a single ultrashort pulse – in essence, the number of photons hitting the sample per unit area for a given photon energy. Unfortunately, 10-3 this fl uence can vary at FELs from shot to shot both in Intensity [arb. units] its total amount as well as in the way it is distributed in a focal spot. Simply put, the footprint of the x-rays on the 10-4 sample can vary in both shape and intensity. This makes quantitative experiments on non-linear processes at x-ray wavelengths very challenging, as they are inher- ently sensitive to the precise fl uence distribution. Fig. 2: 2D detector image downstream of the sample showing To address this issue, we have developed a method both the ring-shaped magnetic scattering as well as the which allows to take a snapshot picture of the fl uence fl uence map (“footprint”) of the soft x-rays on the sam- distribution impinging on the sample while at the same ple generating this magnetic scattering (log scale). time recording the scattering signal of interest generated by that very same FEL shot. The approach relies on the fabrication of very shallow grooves of only a few nano- silicon substrate. The crater is produced under the same meter depth into the membrane holding the sample. Via conditions and alignment as the fl uence map, but neces- a tailored two-dimensional distortion, this groove pattern sarily belongs to a different FEL pulse. In Fig. 2, we show forms a diffractive optical element that is designed to im- the same beam footprint on the sample (visible in two age the footprint of the incident x-ray beam on a two-di- conjugate copies and on a logarithmic intensity scale) mensional detector. An example of such an image taken recorded together with the magnetic scattering from a at the FEL facility FERMI in Trieste, Italy, for 20.8 nm XUV thin-fi lm sample with ferromagnetic domains produced radiation is shown in Fig. 1. The focal spot on the sample on the opposite side of the membrane carrying the grat- exhibits a strong intensity maximum accompanied by a ing optics. The magnetic scattering signal is visible as a number of secondary maxima. We compare this fl uence ring of high intensity. With our approach, we can relate distribution with an atomic-force microscope image of a this scattering signal from the specimen to the exact in- damage crater generated by a single FEL x-ray pulse in a cident fl uence footprint on this sample, as both originate from the identical x-ray pulse.

Furthermore, the use of the grating structure alone – Grating AFM without a sample – turned out to be extremely helpful 1 1 when aligning the x-ray optics of the FEL or a sample relative to the focal position. Together with the downstream detector, the distorted grating provides instant feedback on the beam shape when placed into the x-ray beam. The new method is already now routinely used at Height [µm] the FERMI free-electron laser for alignment purposes.

0 Intensity [arb. units] 0

Fig. 1: Single-shot image of the FEL beam footprint on the sam- Publication ple, recorded at FERMI using a particularly designed grating. As comparison, we show an atomic force micrograph SGP18: M. Schneider, C. M. Günther, B. Pfau, F. Capo- (AFM) of a single-shot damage crater in silicon. Apart from tondi, M. Manfredda, M. Zangrando, N. Mahne, L. Rai- artifacts due to melting and redeposition of the substrate mondi, E. Pedersoli, D. Naumenko, S. Eisebitt; In situ sin- material, the damage crater shows excellent agreement gle-shot diffractive fl uence mapping for X-ray free-elec- with the fl uence map imaged via diffraction. tron laser pulses; Nat. Commun. 9 (2018) 214/1–6

15 OPCPA development at MBI

M. Bock, T. Feng, F. Furch, L. v. Grafenstein, U. Griebner, M. Kretschmar, M. Mero, T. Nagy, V. Petrov, M. Schnürer, J. Tümmler, I. Will, and T. Witting

Exploring of the potential of OPCPA systems is one of the XUV pulses have been produced. The attosecond puls- research activities at the MBI. The OPCPA development es have been characterized with an attosecond streak- was supported by a Sondertatbestand in the 2015-2016 ing experiment. Figure 1(a) shows a measured photo- period resulting from an evaluation panel recommenda- electron spectra as a function of XUV-IR delay. Figure tion. An important aspect of the OPCPA development is 1(b) displays the retrieved trace. In Figure 1(c) the re- that research projects are emphasized whose successful constructed electric field of the IR pulse is shown as a realization benefits the research in topical areas 2 and 3. red line. The blue line indicates the intensity of the XUV Noteworthy examples in the recent past have been the pulse on a logarithmic scale. The main pulse has a du- development of high energy thin-disk lasers, which now ration of 157 as and is accompanied by small satellites serve as the pump source in a multi-TW OPCPA system, spaced at half the period of the IR field as expected from and several OPCPA systems that are now used in MBI’s HHG. In Figure 1(d) the retrieved XUV pulse spectrum research on time-resolved X-ray diffraction, soft X-ray and spectral phase are presented. transient absorption and strong field ionization. Also the already mentioned multi-TW 800 nm OPCPA Presently, a high repetition rate (nrep = 100 kHz) OPCPA system (nrep = 100 Hz) is nearly completed and delivers producing 190 µJ, 7 fs, CEP-stable pulses at 800 nm 30 mJ pulses with a duration of 9 fs. The main compo- has been completed [FWG17, HFW18]. In addition, nent of this OPCPA system is a three stage optical-para- nonlinear pulse compression using gas-filled hollow metric amplifier with BBO crystals up to a maximum core fibers or multi-plate continuum generation [LWH18] aperture of 20 mm x 20 mm. This size is the largest has allowed reaching pulse durations below 4 fs (~ 1.5 available for BBO crystals. These three OPA stages are optical cycles). The system is currently serving as the driven by a two-channel diode-pumped thin-disk laser, drive laser in a high repetition rate attosecond pump- which was developed at the MBI during the last years probe beam-line in which part of the pulse energy is [JTW16]. The initial CEP stable seed pulses are gen- used to generate extreme ultraviolet (XUV) pulses via erated by difference-frequency mixing and white-light high harmonic generation (HHG). Utilizing post-com- generation of pulses originating from the diode-pumped pressed pulses from this OPCPA, isolated attosecond Yb:KGdW master oscillator of the system.

60 60

50 50

40 40

30 30 Energy + Ip [eV] Energy + Ip [eV]

20 20 -10 -5 0 5 10 15 -10 -5 0 5 10 15 τ [fs] τ [fs]

2 0.8

2 0

[t]|

2 0.6 )| xuv )) [rad] ω ω ( -2 0.4 ( xuv xuv of |E |E 10 -4 0.2 log arg(E

-6 0 -6 -4 -2 0 2 4 6 20 30 40 50 60 Time [fs] Photon energy [eV]

Fig. 1: Preliminary characterization of isolated attosecond pulses at 100 kHz. (a) Measured photoelectron spectra as a function of delay between the XUV and IR pulses. (b) Reconstructed trace using a ptychography-based algorithm. (c) Retrieved XUV pulse envelope and IR electric field. (d) Retrieved XUV pulse spectrum and spectral phase.

16 (a) (b) 2800 (a) 0.0 1.01.0 (b) 11.0.0 measured measured 3 0.2 3 ) 2625 n m

( 0.3 ) )

reconstructed h . . 2450 0.5 e n g t m m 0.7 r ) r

W a v e l 2275 o d o 0 0 0.8 n a n 1.0 ( r 2100 (

( -230 -115 0 115 230 80 fs

y Time delay (fs) y t t 0.50.5 00.5.5 2800 0.0 s e retrieved s i

s i -3 0.2 a ) -3 n

n 2625 n m h Phase [rad] e

( 0.3 e t h t

P 2450 0.5 n Intensity [norm.] Intensity [norm.] n e n g t I I -6 0.7

W a v e l 2275 -6 0.8 2100 1.0 -230 -115 0 115 230 Time delay (fs) 0.00.0 00.0.0 44500500 55000000 55005500 66000000 -8-80000 - -600600 --400400 --200200 0 200200 WWavelengthavelength [nm](nm ) TTimeime [fs](fs ) Fig. 2: SHG-FROG characterization of the compressed 5 µm pulses at a 1-mJ energy level. (a), (b) SHG-FROG trace measured and retrieved; (a) optical spectrum, measured (grey), retrieved (blue) and phase (red); (b) retrieved temporal pulse shape, Insets: SHG-FROG trace measured and retrieved

The OPCPA system is now available for experiments has already delivered an unprecedented average pow- and has been installed in a large laser laboratory which er of 43 W at the 1.55 µm signal wavelength, in 51 fs provides suffi cient space for a large focusing distance long, passively CEP-stabilized laser pulses, accompa- between 5 m and 10 m. This length is required for fo- nied by 12.5 W, 73 fs, 3.1 µm idler pulses [MHP18]. The cusing the high-power output beam into a long-pass long-term RMS average power stability of both beams is gas cell for generating high harmonics with an unprec- below 0.5 %, when measured by a power meter. Long- edented high photon number per pulse. This high pho- term power and intensity stability are further corroborat- ton number per pulse will enable the study of nonlinear ed by strong-fi eld ionization experiments using 8 W of processes in the XUV regime on the attosecond time- the 1.55 μm signal beam and a reaction microscope as scales, as well as single-shot coherent diffractive imag- particle detector. Figure 3 shows the rate of generation ing of isolated nanoparticles and ultrafast light induced of Ar+ ions as a function of time, where each data point electron dynamics within them. The multi-TW-OPCPA was taken at an integration time of 1 s. After shot noise system is maintained with minor readjustment during a subtraction, the remaining fl uctuations correspond to a whole working day. Currently, a beamline is under com- standard deviation of only 3.1 %. missioning for the generation of high harmonic pulses with energy on the microjoule level, aiming for the envi- Within the Nanomovie EFRE project, a 10 kHz, 2.1 µm sioned XUV-induced nonlinear optics experiments (see OPCPA system is under development, which is expect- project 2.1). ed to lead to the delivery of at least 3 mJ, few-cycle laser pulses in the near future. This system aims to provide The ongoing OPCPA developments include a midwave-IR (MWIR) OPCPA system operating at 1 kHz, to be used as driver laser for the Cu Kα source utilized in MBI’s time-resolved X-ray diffraction research (see proj- 3000 ect 3.3). This system, funded through a grant in the competitive Leibniz SAW scheme, is at an advanced stage 2500 of development and has already demonstrated 80 fs, 2000 3.5 mJ pulses, translating into a peak power of several 1500

tens of GW, which represents a new peak performance rate [Hz] + 1000 level at this wavelength [BGG18, GMU17]. The mea- Ar sured spectrum and the characterization of the com- 500 pressed 5-µm idler pulses at a 1-mJ energy level by the 0 SHG-FROG technique are presented in Fig. 2. 0.00 0.25 0.50 0.75 1.00 1.25 0 10 20 30 Time [hours] Counts Future development of this system will seek further power scaling, as well as post-compression of the 3 µm signal and 5 µm idler pulses. Other long wavelength OPCPA Fig. 3: systems that are in development are motivated by MBI’s Characterization of the long-term power stability of the research utilizing HHG in the water window for soft X-ray 100 kHz, 1.55 µm OPCPA using a reaction microscope transient absorption studies. This includes a 1.55 μm with a power of 8 W from the laser beam. The photon signal/3.1 μm idler dual-beam OPCPA system operating energy at 1.55 µm is 0.80 eV, while the ionization po- at 100 kHz that was also funded through a grant in the tential of Ar is 15.76 eV. competitive Leibniz SAW scheme. To date, this system

17 high photon flux in the water window as the basis for a new application laboratory. Furthermore, Nanomovie’s objective comprises a second system targeting even higher photon energies allowing for spectroscopic access to 3d transition metal L-edges. Both systems feature a monolithic – single pump laser – concept built on advanced commercial products, pushing the power limits with own developments.

OPCPA will moreover be used to develop intense broadband mid-infrared sources for use in 2D-IR spectroscopy in the molecular fingerprint region. In recent years, in connection with the development of the MWIR OPCPA at 5 µm, MBI has made significant progress in the development of 2-µm picosecond pump lasers based on Ho:YLF chirped pulse amplifiers reaching more than 10 GW peak power [GMU16]. Using these systems, parametric generation in small bandgap nonlinear materials is performed, avoiding the two-photon absorption problem. In the near future idler wavelengths up to 8 µm will be explored.

Publication

FWG17: F. J. Furch, T. Witting, A. Giree, C. Luan, F. Schell, G. Arisholm, C. P. Schulz, and M. J. J. Vrakking, Optics Letters 42 (2017) 2495

HFW18: D. Hoff, F. J. Furch, T. Witting, K. Ruhle, D. Adolph, A. M. Sayler, M. J. J. Vrakking, G. G. Paulus, and C. P. Schulz, Optics Letters 43 (2018) 3850

LWH18: C.-H. Lu, T. Witting, A. Husakou, M. J.J. Vrak- king, A. H. Kung, F. J. Furch, Optics Express 26 (2018) 8941

BGG18: M. Bock, L. von Grafenstein, U. Griebner, and T. Elsaesser, Journal of the Optical Society of America B 35 (2018) C18

GMU17: L. von Grafenstein, M. Bock, D. Ueberschaer, K. Zawilski, P. Schunemann, U. Griebner, and T. El- saesser, Optics Letters 42 (2017) 3796

MHP18: M. Mero, Z. Heiner, V. Petrov, H. Rottke, F. Branchi, G. M. Thomas, and M. J. J. Vrakking, Optics Letters 43 (2018) 5246

GMU16: L. von Grafenstein, M. Bock, D. Ueberschaer, U. Griebner, and T. Elsaesser, Optics Letters 41 (2016) 4668

JTW16: R. Jung, J. Tümmler, and I. Will, Opt. Ex- press 24 (2016) 883

18 High harmonic spectroscopy of the Mott phase transition in a strongly correlated solid

R. Silva, A. Himenez-Galan, O. Smirnova, and M. Ivanov

Traditionally, phase transitions have been viewed as So far, all work along the second avenue dealt with ef- a discontinuity in a state of an infi nitely large system at fectively single-particle response. The highlighted work the thermodynamic equilibrium. This perspective has presents the fi rst analysis of high harmonic generation in changed recently with the advent of dynamical quantum strongly correlated solids that cannot be described by the phase transitions in fi nite systems shaken out of their equi- familiar band structure. It shows that high harmonic spec- librium. While this concept is now maturing, the search trum in such systems can be qualitatively different from for observables and approaches best suited to image the that familiar in weakly correlated solids, and that the emis- dynamics of such transitions with few-femtosecond accu- sion has a many-particle origin. racy remains elusive. When a correlated system, such as the canonical Mott The highlighted work shows that highly nonlinear opti- insulator, is subject to a suffi ciently strong electric fi eld, cal response, high harmonic generation, can be used to the applied voltage can break its insulating, strongly cor- time-resolve light-induced phase transition in a canonical related anti-ferromagnetic ground state and turn it into a strongly correlated system, the Fermi-Hubbard lattice. paramagnetic conductor. The time resolution can be as good as a femtosecond, far better than a single cycle of the light electric fi eld trigger- In this process, two-electron excitations, known as dou- ing the phase transition. Thus, it offers a practical tool for blons, are created. These quasi-particles are promoted to achieving the elusive goal of resolving a phase transition the fi rst excited Hubbard band of the strongly correlated in a quantum system. solid. From this excited band, they can recombine with the holes created in the ground state. Recombination leads to The recently discovered high harmonic generation in sol- light emission, converting the energy absorbed from the ids has opened two major research avenues. The fi rst intense low-frequency driving fi eld into its high harmonics. aims at developing all solid-state light sources and optoelectronic devices where the optical response is tailored Importantly, when the high harmonic emission is time-re- on the sub-cycle and sub-wavelength scale. The second solved, one fi nds that it does not begin until the onset of aims at imaging ultrafast light-driven charge fl ow in solid the phase transition. What is more, it ends at the end of state systems, taking advantage of modern experimen- the phase transition, when the correlated ground state is tal tools for complete time-domain characterization of the destroyed. Thus, high harmonic emission time-resolves emitted light. The dynamics of light emission maps out the the destruction of the anti-ferromagnetic order and the dynamics of the charge fl ow. Importantly, the work along emergence of liquid-like paramagnetic state, following this second research avenue provides the foundation for correlated spin dynamics with few femtosecond accuracy. the advances along the fi rst research avenue. In particular, the work also fi nds that high harmonic spectra trace the ultrafast changes of the order parameter – the 1.0 0.2 number of the doublon-hole pairs per site, and that it refl ects 0.5 0.1 the Loschmidt echo associated with the phase transition. Fidelity

dh pairs 60 10-9 In general, this work introduces high harmonic spectroscopy as a tool to time-resolve highly non-equilibrium ma- 40 10-10 ny body dynamics in strongly correlated system, with few femtosecond accuracy. In doing so, it brings together two 20 10-11 topics that, until now, have been the focus of intense but

Harmonic order non-overlapping research efforts: high harmonic genera- 0 10-12 tion in solids and strongly correlated dynamics. 0 100 200 300 Time [fs] Correlated spin and charge dynamics are central to dy- Fig. 1: namics in condensed matter systems. High harmonic High harmonic spectroscopy of light-induced phase transi- generation offers new and unexpected ultrafast camera tion. The bottom panel shows time-frequency reconstruc- for capturing these dynamics with unprecedented tempo- tion of the emitted high frequency light. The vertical red ral resolution. line in the bottom panel shows when the laser electric fi eld (yellow oscillating curve) crosses the threshold fi eld, de- stroying the insulating phase of the material. The top panel shows the average number of doublon-hole pairs per site Publication (blue) and the decay of the insulating fi eld-free ground state (red). The mission starts when the doublons begin SBR18: R. E. F. Silva, I. V. Blinov, A. N. Rubtsov, O. to get excited out of the ground state, and ends when the Smirnova, and M. Ivanov; ‘’High-harmonic spectroscopy ground state is destroyed. of ultrafast many-body dynamics in strongly correlated systems’’; Nature Photonics 12 (2018) 266

19 Laser-driven electron recollision remembers molecular orbital structure

F. Schell, T. Bredtmann, C. P. Schulz, S. Patchkovskii, M. J. J. Vrakking, and J. Mikosch

State-of-the-art experiments and numerical simulations izing, 0.55 ps long near-infrared (800 nm wavelength) have been combined to test a fundamental assumption laser pulse. This laser pulse induced the formation of a underlying strong-field physics. These results refine our rotational wavepacket accompanied by the alignment of understanding of strong-field processes such as high the molecules during the (full and fractional) rotational harmonic generation and laser-induced electron diffrac- revivals of the wavepacket. During the first half-revival tion. the aligned molecules were exposed to an intense, 40 fs long, 1.29 µm wavelength laser pulse, which removed According to the widely used three-step model of strong- one of the electrons from the molecule (ionization). field physics, strong infrared laser pulses can extract an The momentum of the photoelectron was measured as electron from a molecule (ionization), accelerate it away a function of the angle between the linear polarization into free space before turning it around (propagation), of the alignment laser and the linear polarization of the and finally make it collide with the molecule (recollision). ionization laser, allowing the reconstruction of the kinetic In the recollision step, the electron may recombine with energy distribution in the molecular frame. The kinetic the parent ion, giving rise to high harmonic generation energy distribution contained two characteristic contri- and the formation of attosecond laser pulses, or it may butions, namely a low energy part, reflecting ionization scatter inelastically or elastically. In the latter case, scat- events where no electron-ion collision had taken place, tering from individual atoms within the molecule creates and a high energy part, reflecting ionization events where the possibility that the molecular structure is encoded in an elastic recollision had taken place. the angular distribution of the scattered photoelectrons, a process commonly referred to as laser-induced elec- Photoelectrons were selected which were measured in tron diffraction (LIED). coincidence with either a parent molecular ion or specific fragment ions. Importantly, this allowed to distin- One of the commonly used assumptions underlying the guish whether the photoelectron was removed from the analysis of attosecond physics and LIED experiments is highest-occupied molecular orbital (HOMO) or from the that in the propagation step any information on the initial next-highest-occupied molecular orbital (HOMO-1). The state of the ionized electron is lost. For example, it is end result was that the molecular-frame probability of commonly assumed that any information on the orbital ionization and recollision could be measured separately from which the electron originates is "washed out" during for the removal of an electron from the HOMO and HO- the propagation step, and no longer influences the rec- MO-1. This allowed a determination of the absolute val- ollision process. However, this assumption was so far ue of the high-angle rescattering probability for electrons never experimentally verified. A combined experimental from both orbitals, in the molecular frame. Remarkably, and theoretical study investigating strong-field driven these probabilities turned out to be quite different for the electron recollisions in the 1,3-trans-butadiene molecule HOMO and the HOMO-1 ionization channel. High-level has now done so, with a surprising result. theoretical simulations were performed and confirmed the experimental result. In the experiment, 1,3-trans-butadiene molecules were first aligned along a specified laboratory-frame axis, us- We may conclude that in laser-driven electron recolli- ing the interaction of the molecule with a strong, non-ion- sion the returning electron contains detailed information about the molecular orbital from which it was removed. In particular, nodal planes in this orbital are carried over into the shape of the returning photoelectron wavepacket and strongly influence the recollision probability. It follows that an analysis of laser-induced electron diffraction experiments needs to pay careful attention to the shapes of the molecular orbitals from which the electrons are removed, including possible changes of these shapes in the presence of a strong laser field and/ or as a result of laser-induced changes in the molecular structure.

Publication Fig. 1: Continuum electronic wavepackets for strong-field ion- SBS18a: F. Schell, T. Bredtmann, C. P. Schulz, S. Patc- ization from two different orbitals in 1,3-trans-butadiene, hkovskii, M. J. J. Vrakking, and J. Mikosch; Molecular shortly after ionization. orbital imprint in laser-driven electron recollision; Sci. Adv. 4 (2018) eaap8148/1-8

20 Magnetic nanostructures in ferrimagnets: fast and small

L. Caretta1, M. Mann1, F. Büttner1, K. Ueda1, B. Pfau2, C. M. Günther2,3, P. Hessing2, A. Churikova1, C. Klose2, M. Schneider2, D. Engel2, C. Marcus1, D. Bono1, K. Bagschik4, S. Eisebitt2,3, and G. S. D. Beach1 1Massachusetts Institute of Technology, Cambridge, USA, 2Max-Born-Institut, Berlin, Germany, 3Technische Universität Berlin, Berlin, Germany, 4Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany.

One vision for a novel concept to store data magneti- from spin separation and injection via the spin Hall ef- cally is to send small magnetic bits back and forth along fect. We achieved record high speeds of the domain wall a track in a memory chip via current pulses, in order motion exceeding 1.3 km/s. to store the information at a suitable place in the chip and retrieve it later. For quite some time, the research In a second experiment, current injection into the strip- towards the realization of this concept focused on fer- line was used to create ultra-small, spiral, disk-shaped romagnetic materials for the magnetic race track. How- magnetization structures – so called skyrmions – in the ever, these materials show fundamental limitations: the stripline starting from a homogeneous magnetization minimum size of the ferromagnetic bits is limited by the state. We used Fourier-transform holography with soft strong magnetic stray fi eld and the maximum speed the x-rays at 1.6 nm wavelength to make the nanometer- bits can be moved at is limited by the precessional dy- scale skyrmions in the stripline visible, investigating the namics in ferromagnets. current-induced nucleation, size and stability. The lens- less imaging method is based on the interference of co- Antiferromagnets, exhibiting opposing magnetic mo- herent x-rays scattered from the object and an additional ments of neighboring atoms, have been proposed as reference beam emerging from a tiny pinhole next to the alternative material class as they lack the stray fi eld as- object. Magnetization contrast is achieved by tuning the sociated with a net magnetic moment and exhibit much wavelength of the radiation to particular electronic ex- faster magnetization dynamics. However, manipulating citations of the magnetized element (here Co) and by (e.g., moving) and detecting antiferromagnetic domains using circularly polarized x-rays. is very challenging for the same reason.

In our work, we demonstrate that ferrimagnets can be used to overcome the limitations of both ferro- and anti- ferromagnetic materials. In contrast to antiferromagnets, the opposing magnetic moments in a ferrimagnet are unequal and often carried by different atomic species in the material. In this case, the remaining net magnetization is a function of temperature and only at a particular temperature, where the moments carried by the different magnetic sublattices have the same magnitude, the net magnetic moment vanishes. In general, however, this temperature is different from the temperature where the net angular momentum is compensated, as the spin and orbital moment of the electrons may contribute in different ratios to the magnetic moments of the respective magnetic species in the ferrimagnet.

We have investigated different types of magnetic textures generated in thin striplines (“tracks”) of a Gd44Co56 alloy in contact with a platinum layer. In this material, cobalt and gadolinium form antiferromagnetically coupled sublattices. Importantly, the magnetic and angular momentum compensation points of the alloy nearly co- incide and are located close to room temperature. While magnetic compensation determines the static material properties as domain size, the angular compensation detemines the dynamic properties. This constellation, Fig. 1: thus, allows to overcome the speed and size limits of Schematic confi guration of the magnetic moments – ferromagnets mentioned above while the different mag- represented by arrows in the images – forming a netized atomic species remain individually detectible skyrmion in ferromagnetic (top) and antiferromag- and addressable. netic/ferrimagnetic (bottom) materials. The size of a skyrmion in a ferromagnetic material is larger than In the fi rst experiment conducted at the MIT, the stripline in antiferromagnetically coupled materials where is sectioned into domains of opposite net magnetization, neighboring atoms have approximately opposite separated by domain walls. When sending electric cur- magnetization. In the future, a magnetic skyrmion rent pulses through the platinum layer, the domain walls could encode a logic “1” in data storage. are shifted along the track by spin-orbit torques resulting

21 We could show that indeed the size of the skyrmions in Gd44Co56 can be significantly reduced compared to ferromagnetic materials, as depicted schematically in Fig. 1. Images of skyrmions generated in thin film system are shown in Fig. 2. The smallest skyrmions we observed had a diameter of only 10 nm at room temperature and zero externally applied magnetic field. Such small sizes have previously only been realized at cryogenic temperatures and in the presence of a sizeable magnetic field.

The ability to generate small magnetic textures in ferrimagnets and to move them efficiently demonstrated in this work underpins the large application potential of ferrimagnetic systems for novel data storage applications.

Fig. 2: Example of nanometer-scale skyrmions created in an ferrimagnetic material imaged with x-ray holography. The size of the smallest skyrmions approaches 10 nm. The image was taken at room temperature and at zero applied magnetic field.

Publication

CMB18: L. Caretta, M. Mann, F. Büttner, K. Ueda, B. Pfau, C. M. Günther, P. Hessing, A. Churikova, C. Klose, M. Schneider, D. Engel, C. Marcus, D. Bono, K. Bag- schik, S. Eisebitt, G. S. D. Beach; Fast current-driven domain walls and small skyrmions in a compensated ferrimagnet; Nat. Nanotech. 13 (2018) 1154–1160

22 Electric polarization in the macroscopic world and electrons moving at atomic scales – a new link from femtosecond x-ray experiments

C. Hauf, A.-A. Hernandez Salvador, M. Holtz, M. Woerner, and T. Elsaesser

Phenomena in the macroscopic world are typically de- direct insight into such dynamics by mapping transient scribed by classical physics while processes at atom- electron distributions at atomic length and time scales ic length and time scales are governed by the laws of [HHH18]. quantum mechanics. The connection between microscopic and macroscopic physical quantities is far from The prototype ferroelectric ammonium sulfate [Fig. 1] being trivial and partly unexplained. was studied in an ultrafast x-ray powder diffraction experiment to follow the motion of charges over distances The electric polarization is a macroscopic quantity which on the order of the diameter of atoms (10-10 m = 100 pi- describes the dipole moment of matter. The polarization cometers) in a quantitative way. In the measurements, originates from the peculiar electron distribution at the an ultrashort excitation pulse sets the atoms of the ma- atomic scale in polar and ionic materials, among them terial, a powder of small crystallites, into vibration. A the most interesting class of ferroelectrics. Their sponta- time-delayed hard x-ray pulse is diffracted from the ex- neous electric polarization is widely applied in electronic cited sample and measures the momentary atomic ar- sensors, memories, and switching devices. The link be- rangement in form of an x-ray diffraction pattern. From tween polarizations, in particular time dependent ones, such patterns, the momentary electron distribution and microscopic electron densities is important for un- is derived by a numerical method the so-called max- derstanding and tailoring the properties of ferroelectrics. imum entropy method (MEM). This analysis provides both electron density maps and – via the core electrons Based on a new experimental and theoretical approach, bound to the atoms – vibrational displacements as a research within the MBI project 3.3 has now established function of time (Fig. 2). a direct quantitative connection between macroscopic electric polarizations and time-dependent microscopic electron densities. As reported in Ref. [HWE18], atomic motions in ferroelectrics are launched by optical excitation and modulate the electron distribution on a femtosecond time scale. The resulting dynamics of electron density are mapped by time-resolved x-ray powder diffraction [HHH18]. Such data allow for the generation of temporally and spatially resolved electron density maps from which the momentary macroscopic polarization is derived with the help of a new theoretical concept. The potential of the method is demonstrated with prototype ferroelectric materials.

The theoretical work extends the existing quantum phase approach for calculating stationary macroscopic polarizations towards ultrafast nonequilibrium dynamics of electron charge and polarization. The theoretical key steps consist in deriving a microscopic current density from time-dependent electron density maps while minimizing the electron kinetic energy, and calculating the macroscopic polarization from current density. This Fig. 1: method is applied to the prototype ferroelectric materi- Top: Crystal lattice of ferroelectric ammonium sulfate + al ammonium sulfate [(NH4)2SO4, Fig. 1] and a second [(NH4)2SO4] with tilted ammonium (NH4 ) tetrahedra 2- prototype system, potassium dihydrogen phosphate (nitrogen: blue, hydrogen: white) and sulfate (SO4 ) [KH2PO4, not shown]. The analysis provides both mi- tetrahedra (sulfur: yellow, oxygen: red). The green ar- croscopic and macroscopic polarization changes and row shows the direction of macroscopic polarization P. their absolute values as governed by microscopic vibra- Blue arrows: local dipoles between sulfur and oxygen tions. The results establish ultrafast x-ray diffraction as atoms. The electron density maps shown in the bottom a unique tool for grasping macroscopic electric proper- left panel and the movie are taken in the plane shown ties of complex materials. in grey. Bottom left: Stationary electron density with a high value on the sulfur (red) and smaller values on the The macroscopic electric polarization of ferroelectric oxygen atoms (yellow). Bottom right: Change of local crystals is due to a superposition of many dipoles at dipoles at a delay time of 2.8 picoseconds (ps) after ex- the atomic scale which originate from spatially sepa- citation of the ammonium sulfate sample. An anisotropic rated electrons and atomic nuclei. The macroscopic shift of charge reduces the dipole pointing to the right polarization is expected to change when the atoms are and increases the other 3 dipoles. set in motion. Femtosecond x-ray diffraction provides

23 0 12000 [pm] s-o d S-O Bond Length Change ] -

t = +2.8 ps Q [ t ] [0.001 e Charge Change on (SO3)O ηΔ

] Polarization Change -2 [mC m t = +3.9 ps c Δ P

-2 0 2 4 6 8 Time [picoseconds]

Fig. 3: Upper panel: Change of the S-O bond length as a - 3 ηΔρ [r,t] [e /nm ] function of the delay time. The maximum change of 0.1 pm is 1000 times smaller than the bond length +60 +30 0 -30 -60 itself, i.e., the atomic motions cannot be observed in Fig. 2. Middle panel: Charge transfer from one

Fig. 2: oxygen atom to the SO3 group of the sulfate ion (left (a) Stationary electron density in the grey plane black arrows in Fig. 2) as a function of delay time. shown in Fig. 1. (b) Change of electron density at a Lower panel: Change of the macroscopic polarization delay time of 2.8 picoseconds (ps) after excitation P along the c axis which is the sum of all microscopic of the ammonium sulfate crystallites. The circles dipole changes of the local S-O dipoles within the sul- mark the atomic positions, the black arrows indicate fate ions (red and blue arrows in Fig. 1 bottom right). the transfer of electronic charge between one of the

oxygen atom and the SO3 group of a single sulfate ion. The vibrational displacements of the atoms are The results establish time-resolved ultrafast x-ray dif- smaller than the line thickness of the circles and, fraction as a method for linking atomic-scale charge thus, invisible on this length scale. (c) The reverse dynamics to macroscopic electric properties. This novel charge transfer occurs at a delay time of 3.9 ps. strategy allows for testing quantum-mechanical calculations of electric properties and for characterizing a large class of polar and/or ionic materials in view of their po- The electron density maps show that electrons move tential for high-speed electronics.. over distances of 10-10 m between atoms which are more than a thousand times larger than their displacements during the vibrations [Fig. 3]. This behavior is due to the complex interplay of local electric fi elds with Publication the polarizable electron clouds around the atoms and determines the momentary electric dipole at the atom- HHH18: C. Hauf, A.-A. Hernandez Salvador, M. Holtz, ic scale. Applying the novel theoretical concept dis- M. Woerner, and T. Elsaesser; Soft-mode driven polarity cussed above, the time-dependent charge distribution reversal in ferroelectrics mapped by ultrafast x-ray dif- in the atomic world is linked to the macroscopic electric fraction; Struct. Dyn. 5 (2018) 024501/1-11 polarization [Fig. 3]. The latter is strongly modulated by the tiny atomic vibrations and fully reverses its sign in HWE18: C. Hauf, M. Woerner, and T. Elsaesser; Mac- time with the atomic motions. The modulation frequen- roscopic electric polarization and microscopic electron cy of 300 GHz is set by the frequency of the atomic dynamics: Quantitative insight from femtosecond x-ray vibrations and corresponds to a full reversal of the mi- diffraction; Phys. Rev. B 98 (2018) 054306/1-12 (Edi- croscopic polarization within 1.5 ps, much faster than tor’s Suggestion) any existing ferroelectric switching device. At the surface of a crystallite, the maximum electric polarization generates an electric fi eld of approximately 700 million volts per meter.

24 Photoexcitation circular dichroism in chiral molecules

A. Ordonez, A. Harvey, O. Smirnova

Just like our left and right hands, molecules also often come in two forms, left-handed and right-handed. These forms are connected to each other by mirror reflection. And, just like with our right and left hands, a left-handed molecule cannot be superimposed onto a right-handed molecule by any rotation.

We have known that molecules can be chiral since the XIXth century. Perhaps the most famous XXth century example of a chiral molecule is DNA, whose structure resembles a right-handed corkscrew. In fact, a molecule's handedness is far more important than that of our hands: some substances will be either toxic or beneficial Fig. 1: depending on which "mirror-twin", or enantiomer, is pres- Following excitation by an ultra-short circularly polarized ent. Certain medicines must therefore contain exclusive- laser pulse, electrons follow a right or left helix depend- ly the right-handed or the left-handed enantiomer. ing on the handedness of the molecular structure.

This is why identifying and separating right-handed and left-handed molecules is a crucial step for many appli- The generated helical motion can now be probed by a cations. The difficulty and the challenge arise because second, probe, laser pulse. This probe can be linear- the right-handed and left-handed molecules behave ex- ly polarized, so as not to disrupt the already developed actly the same, unless they interact with another chiral corkscrew motion. The probe also has to be short, so object. Alternatively, they can be distinguished using a that it can catch the direction of the electron motion. chiral experimental setup, where the laser electric field Finally, it should have enough photon energy to knock and the detectors form a chiral reference frame. the excited electrons out of the molecule. Depending on whether the electrons were moving clockwise or anti- Conventionally, when using optical means, chirality clockwise with respect to the corkscrew axis, i.e. with is determined by applying a circularly polarised light, respect to the propagation direction of the pump, the which is also chiral. Indeed, the rotation of the electric liberated electrons will fly out of the molecule along or field vector in a circularly polarized light wave forms a opposite to this direction. right or left "corkscrew", with the corkscrew axis along the direction of the light propagation. This chiral light is This allows one to determine the chirality of the mole- absorbed differently by molecules of opposite handed- cules very efficiently, with a signal 1000 times stronger ness. The effect, however, is very small, because the than with the standard absorption circular dichroism. wavelength of light is much longer than the size of a What's more, this setup could allow one to initiate chi- molecule: the light's corkscrew is too big to sense effi- ral chemical reactions and follow them in time. It comes ciently the molecule's chiral structure. down to applying very short laser pulses with just the right carrier frequency. The highlighted work done by an international research team (CELIA-CNRS/INRS/Max Born Institute/SOLEIL) presents a new and very sensitive method. It uses ultrashort laser pulses to excite electrons in molecules into a Publication twisting motion, the direction of which reveals the molecules' handedness. In contrast to the light helix, here the BCD18: S. Beaulieu, A. Comby, D. Descamps, B. Fab- chiral motion is excited by the molecule itself, which has re, G. A. Garcia, R. Geneaux, A. G. Harvey, F. Legare, just the right size to do it. Z. Mašín, L. Nahon, A. F. Ordonez, S. Petit, B. Pons, Y. Mairesse, O. Smirnova, and V. Blanchet; Photoexci- Excitation by an ultrashort circularly polarized pump tation Circular Dichroism in Chiral Molecules; Nat. Phys. pulse generates a wavepacket. For very short pump 14 (2018) 484 pulses, such wavepacket would occupy several electronic states. The electrons' motion starts in a circle, following the circularly polarized exciting electric field. However, in a chiral molecule it quickly develops into a right-handed or left-handed helix, depending on the handedness of the molecular structure they reside in. The efficiency of this conversion can be close touni- ty, and the team has developed analytical theory which quantifies the molecular properties responsible for such an efficient conversion.

25 26 Short Description of Research Projects

27 28 1.1: Fundamentals of Extreme Photonics

F. Intravaia, O. Smirnova, B. Fingerhut (project coordinators) and M. Ivanov, K.Busch, M. Oelschläger, A. Perez-Leija, D. Reiche, P. Varytis, C. Egerland, T. Bredtmann, S. Patchkovskii, A. Jimenez-Galan, S. Carlstroem, W. Becker, D. Milosevic, H. Reiss, F. Morales, I. Babushkin, D. Ayuso, A. Ordonez, Maria Richter, A. Harvey, J. Kaushal, A. Andreev, J. Herrmann, A. Gusakov, M. Richter, M. Osswald, N. Acharyya, R. Ovcharenko, S. Sharma, N. Singh, P. Elliott, Q. Li, S. Solovyev

1. Overview cow, UA Madrid, U Trieste, Open University, XLIM Li- moges, U Sherbrook, ETH Zurich, University of Central The main objective of the project 1.1 is the development Florida, UPMC Paris, U Sarajevo, U Geneva, MPI Halle, of analytical and numerical methods for the description Hebrew University of Jerusalem, U Rostock. of light-matter interactions in extreme conditions. The number of photons in a light field incident on a system can range from zero (vacuum fluctuations), to just a few (quantum electrodynamics and quantum optics regime), 3. Results in 2018 to hundreds and thousands of absorbed or emitted photons during the interaction with very intense light fields. For each of the general directions, representative high- When a low number of photons are involved, the quan- lights are given below. tum properties of matter and light play very important role in the description of the interaction. At high intensities, the description of light as a classical electromagnetic T1-T2: Light amplification inside laser filaments: wave is adequate, but a precise description of the (often “not so free, free electron lasing.” highly nonlinear) quantum response of matter is needed. Non-perturbative theoretical models and methods are de- Propagation of powerful infrared laser pulses in gases, veloped and applied, focusing on adequate description of such as air, leads to several important nonlinear effects, system’s optical properties and geometrical structure, as including self-focusing, nonlinear ionization of the gas well as on many-body effects such as electron-electron (optical tunnelling) leading to plasma formation and de- correlation, coupled electronic and nuclear dynamics, op- focusing of the beam, and spectral broadening. In par- tically induced and controlled spin dynamics, and the role ticular, the balance of self-focusing and plasma-induced of quantum coherence in these dynamics. The range of defocusing can generate laser filaments, the self-sup- material systems involves atoms, molecules, solids, and porting laser-induced waveguides that can the laser photonic structures such as waveguides. pulse without much diffraction over long distances.

One intriguing phenomenon observed inside laser filaments is the generation and amplification of light at fre- 2. Topics and collaborations quencies substantially different from the spectral con- In 2018 the project was organized around four general tent of the incident laser pulse. There is no consensus directions: yet regarding the main physical mechanism responsible for this phenomenon. In fact, several physical mecha- T1: Theory of attosecond and few-femtosecond nisms are likely at play. electron dynamics We have theoretically proposed a new lasing mechanism T2: Theory of matter in intense laser fields in high-intensity fields [MMP18], following up on our previous work [RPM13, BCB16, BPI16]. The new lasing mech- T3: Theoretical Optics and Photonics in structured anism is general and should be operative in both atomic media (Joint HU-MBI Group) and molecular gases. Together with our experimental colleagues from University of Geneva, we verified our theo- T4: Bio-molecular dynamics in condensed phase. retical predictions in argon and krypton gases [MMP18].

New direction: In October 2018, a new condensed matter The new lasing mechanism is associated with the ef- theory group (T5) joined the project, focusing on first-prin- ficient formation of the so-called “bound states ofthe ciples computational methods for ultrafast laser-driven free electron” [RPM13] – the laser-dressed Rydberg electron dynamics in solids. These methods are then ap- states which are strongly driven by the laser field, but plied to studying laser-driven and laser-controlled ultra- are still weakly bound to the atomic core. These states fast spin and magnetization dynamics in solids. are formed during optical tunnelling, via the mechanism known as “frustrated tunnel ionization” and discovered In-house collaborations with Projects 1.2, 2.1, 2.2, 2.3, by U. Eichmann and coworkers at the MBI [NGS08]. Af- 3.1, and 3.2. ter the tunnelling electron leaves the ground state and the vicinity of the core via optical tunnelling, its drift mo- External collaborations: IC London, HU Berlin, TU Ber- mentum imposed by the laser field may not be sufficient lin, The Weizmann Institute, CEA Saclay, CELIA and U to overcome the residual attraction to the core. As a re- Bordeaux, U Ottawa, Ohio State University, RQC Mos- sult, the electron gets trapped into the Rydberg states.

29 the range of 500-600 nm. The key pre-requisites for this (a) effect, in infrared driving fi elds, was to maintain the driv- 0.06 ing pulse intensity as constant as possible during the 0.04 pulse, shaping it to have a very rapid rise followed by a fl at top. This has been achieved in the experiment in 0.02 the group of J. P. Wolf (U of Geneva). The laser pulse 0 was pre-shaped in such a way that its propagation and -0.02 nonlinear modifi cation during the onset of fi lamentation would lead to the development of the desired “fl at top” -0.04 shape at the beginning of the fi lament. -0.06

Absorption/gain [a.u.] -0.08 The experiment confi rmed the theoretical expectations, -0.1 leading to observation of lasing at the frequencies absent in the spectrum of the fi eld-free argon or krypton 500 600 700 800 900 atoms, but present in the spectrum of the laser-dressed Wavelength [nm] (b) system. 1.0

0.8 T2/T1:Attosecond polarization recorder for chiral attosecond pulses 0.6 Attosecond science has now made fi rst steps towards 0.4 time-resolved imaging of electron dynamics in the condensed phase. However, time-resolved probing of such

Normalised signal 0.2 fundamental condensed phase processes as magnetization dynamics, spin currents, or chiral interactions 0.0 on the attosecond to few-femtosecond timescales is a dream that requires addressing two major challenges: 500 600 700 800 900 a) generation and b) complete characterization of chiral Wavelength [nm] attosecond pulses – isolated sub-fsec pulses with controlled circular or elliptic polarization. Fig. 1: Strong-fi eld driven light amplifi cation by “bound states What’s more, the fi rst step cannot be made without of the free electron” in argon. The top panel shows the second: no claim of generating such pulses can be areas of gain (negative) and loss (positive), following made without simultaneous measurement of their heli- transient absorption of a broadband probe pulse, for city, degree of polarization (i.e. polarized, partially po- different intensities of the driving 800 nm laser fi eld. larized, or unpolarized), and temporal profi le, with no a Substantial areas of gain develop at intensities just priori assumptions. This is why the development of the above 1014 Wcm-2. The bottom panel shows the calcu- attosecond streak-camera – the prime characterization lated spectrum of the fi lamenting pulse: The blue curve tool for linearly polarized attosecond pulses – has been is the input spectrum at the onset of the fi lament. The so pivotal for the advent of attosecond measurements. green curve shows the output spectrum obtained within Attosecond measurements of chiral interactions and the standard model, i.e. without taking into account the chiral electronic response in solids are now facing sim- dressed Rydberg states. The yellow curve shows the ilar challenge. output spectrum already from the single-atom time-dependent Schrödinger equation, under the action of the Indeed, state of the art experimental setups, including pulse at the onset of the fi lament. Strong new lines in our joint experimental and theoretical work [DJM18, the 500-600 nm spectral region refl ect gain by these JZA18], have now provided robust foundation for the dressed states. generation of circularly polarized XUV light at individual frequencies and attosecond pulse trains. Yet, the second problem – that of characterizing isolated attosecond This physical mechanism is related to the so-called pulses, especially their degree of polarization, i.e. distin- Freeman’s resonances familiar from the weaker-fi eld, guishing polarized from partially polarized light – has so multi-photon ionization regime. In strong fi elds, the frus- far remained unsolved. trated tunnelling mechanism is a time-domain, sub-cycle perspective on electron trapping, while the multipho- In our 2018 work [JDP18] we have developed a solu- ton picture of Freeman’s resonances is its frequency tion to this problem, testing our approach using ab-initio domain counterpart [ZPI17]. simulations. Our approach allows one to measure not only the time-average ellipticity of the attosecond pulse, Importantly, our calculations [MMP18] have shown that but also its instantaneous ellipticity and the degree of such laser-dressed states can acquire population inver- depolarization. The method is fully within the current ex- sion with respect to the lower-lying excited states. Thus, perimental capabilities. From the technical perspective, they were predicted to amplify the fi lamenting laser it uses the attosecond pulse with unknown, and possibly pulse at the frequencies associated with the transitions rapidly changing polarization, together with a linearly between the new laser-dressed, laser-driven states, in polarized infrared probe and extends the standard atto-

30 second streak-camera to angle-resolved measurements will wet the grass in a full circle – irrespective of whether of the photo-electron spectra. These angle- and en- it rotates consistently or not – the analogue of one-pho- ergy-resolved photo-electron spectra are measured as ton ionization with an XUV-only pulse. So, merely look- a function of the time-delay between the attosecond ing at the grass will not reveal whether the sprinkler has pulse and the oscillations of the IR probe, as in the stan- been turning exactly the way it was desired or not. But if dard streak-camera. a “gusty wind” – the linearly polarized IR probe – comes along, then we can distinguish whether the sprinkler has We have shown that the polarization properties of the been turning regularly or irregularly. If the wind blows attosecond pump pulse are mapped onto the left-right alternately from the left or right each time the arm of asymmetry in the photo-electron spectra, with “left” and the sprinkler faces left or right, then the patch of wet “right” defi ned with respect to the linearly polarized in- grass will not be circular, but rather elliptical in shape. A frared probe pulse. According to our calculations, the sprinkler rotating completely irregularly would leave an asymmetry faithfully encodes the complete polarization ellipse on the grass stretched in the wind direction, while state of the attosecond pump pulse. a regularly rotating sprinkler will display a tilted ellipse. This forms the basic idea behind the reconstruction.

The results shown in Fig. 2 demonstrate the capabilities of the reconstruction procedure. We have considered a 250 asec pulse carried at 41 eV (vector potential is shown in the fi gure). Ellipticity varies from ϵ = 0.3 along the y-axis to ϵ = 0.625 along the x-axis. Excellent agreement between the input and the retrieved pulse is achieved.

T2/T1: Generation and probing of orbital momentum polarized hole dynamics in optical tunneling

As we have shown theoretically previously, tunnel ionization of noble gas atoms driven by a strong circularly polarized laser fi eld generates spin (s) and angular momentum (l) polarized electronic wavepackets [BS11, BS13, HMK16]. The electronic wavepackets are correlated to the spin (S) and orbital angular momentum (L) - polarized holes, generated in the valence shells of the ionizing parent atoms. The liberated electrons are spun away by the strong laser fi eld, but the L- and S-polarized holes remain. Notably, while spin-polarization may be rather weak in atoms with weak spin-orbit interaction, such as e.g. Argon, the orbital angular momentum (L) Fig. 2: polarization is not. Even in the case of weak spin-orbit Attosecond recorder of the polarization state of light. coupling, it leads to nontrivial hole dynamics, with char- Top panel shows the set-up: elliptically polarized isolat- acteristic period of about 28 fs in Argon. ed attosecond pulse ionizes the atom in the presence of linearly polarized IR pulse. Angle-resolved photo-elec- In 2018, we have developed detailed analytical theory

tron spectra are recorded. The moments t1, t2, t3 depict and numerical analysis of how the emergence of L-po- the characteristic instants responsible for the electrons larized holes can be probed [EKR18]. This theoretical

with maximum perpendicular (t1, t3) and parallel (t2) work was done in collaboration with experiments per-

velocities. The timing of t1 and t3 is sensitive to the di- formed in the group of R. Doerner (U Frankfurt). The rection of rotation of the XUV pulse and the oscillations L-polarized holes where generated by circularly polar- of the IR. Bottom panel shows incident (black) and re- ized pulse carried at 400 nm. Then, an intense circularly constructed (blue) attosecond pulses. polarized pulse, carried at 800 nm, was used to probe the presence of the hole L-polarization. To this end, the polarization of the probe was altered relative to that of The concept of the method can be described as follows: the pump. Energy-resolved photo-electron spectra cor- as the light pulse knocks an electron out of the atom, the related to the doubly charged argon ions have been re- electron wavepacket carries the information about the corded as a function of the relative polarization between ionizing fi eld. Because the ionizing fi eld is circularly po- the pump and the probe, see Fig. 3. Unfortunately, the larized, the ejected electrons also fl y off with a rotating ~40-fs durations of the pump and the probe pulses motion. One can compare the electrons being ejected where too long to resolve the spin-orbit dynamics, but with water sprayed by a sprinkler, which either continues enough to resolve the propensity rules in optical tunnel- turning in the direction you want it to, or which keeps ing and the arising L-polarization. stuttering and even changing its direction (imperfectly polarized pulse or pulse with time-dependent polariza- Theoretically, the preference is for liberating the elec- tion). If the sprinkler is allowed to run for a while, then it tron counter-rotating with respect to the fi eld. The ener

31 dynamics and the spin ring-currents induced by optical tunneling in circularly polarized fi elds. This can be done within similar pump-probe setup, but using few-cy- 1 cle pump and probe pulses.

0.8

m = -1] T3: Endurance of two-particle coherence in open 0.6 systems

0.4 The research of the T3 group in 2018 has been centered around two main topics. The fi rst is the nonlinear and Yield [norm. to Yield 0.2 quantum plasmonics in nano-structures. The second is quantum photonics and few-photon nonlinearities in 0 photonic structures such as waveguides. 0 10 20 30 40 50 60 Energy [eV] One of the 2018 highlights was the theoretical analysis of how coupled waveguides can be used as a quantum simulator, to replicate dynamics of an entangled quan- Fig. 3: tum system coupled to environment [PGL18]. A very Probing generation of L-polarized electrons and holes interesting result was the discovered endurance of the in optical tunneling. The blue and the orange curves initial coherence in the entangled wavefunction, in spite (data points) show theoretical (experimental) results of entanglement loss. This work has been done in a for the electron spectra correlated to the generation collaboration with the experimental group of A. Szameit of the doubly-charged argon ion Ar++ in a two-pulse (Univ. of Rostock). experiment. The blue color shows ionization from the orbital rotating against the polarization of the circularly Experimentally, it is now possible to inscribe extremely polarized 800 nm fi eld, ionizing the Ar+ ion. The ion is low-loss single mode waveguides into glass chips, with prepared by the circularly polarized 400 nm pump. The full control not only over the exact position where the orange color shows ionization from the orbital co-rotat- waveguides are written, but also over their refractive ing with the polarization of the circularly polarized 800 index, including controlled index variations along the nm probe, ionizing Ar+. TDSE and ARM denote numeri- waveguides. cal (TDSE) and analytical (ARM) calculations. In paraxial approximation, waveguides are described by an effective Schrödinger equation in which the propaga- gy-resolved electron spectrum is also distinctly different tion coordinate plays the role of time. Each waveguide for the co- and counter-rotating electrons: it is shifted to represents a node in a coupled tight-binding two-dimen- higher energies when a co-rotating electron is removed. sional network. The quantum dynamics is mapped onto Thus, if the polarization of the probe is counter-rotating the propagation of photons injected into the waveguides with respect to the pump, the probability of the second and it can be monitored at any distance. ionization step will be higher and the photo-electron spectrum will be at lower energies, exactly as found in the Randomly varying the writing velocity of each wave- experiment and in the theoretical calculations, see Fig. 3. guide (thus varying the propagation constant) “dynamic disorder” is readily induced. It effectively simulates This work provided the decisive confi rmation of our pre- dephasing processes due to random “time-dependent” dictions regarding the unusual propensity rules in optical potentials. tunneling, and the strong infl uence of the initial orbital on both the tunneling probability and also on the photoelec- Importantly, in these photonic confi gurations one can tron spectrum. The next logical step would be to perform launch various types of initial conditions: single photons, experiments aimed at time-resolving the spin-orbit hole classical light, distinguishable and indistinguishable,

Fig. 4: Photonic quantum simulator for single-particle and entangled two-particle dynamics. Each waveguide represents a site in a 3-site tight-binding network, and propagation distance correlates to time in quantum evolution. Different input states can be introduced, such as a single-photon wavepacket into a single waveguide or an entangled state where two photons are sent either into the left top or the right top waveguide.

32 form of entanglement) were found to evolve towards the same final state, where there still is quantum coherence 1.0 due to particle indistinguishability, leading to non-zero 0.8 off-diagonal elements in the full density matrix characterizing the system. Moreover, the diagonal elements of 0.6 the density matrix show photon bunching. The off-diagonal elements would be zero in the absence of quantum 0.4 coherence, and the initial classical input leads to photon 0.2 anti-bunching. The bunching and anti-bunching in the Intensity [arb. u.] two cases were confirmed by the Univ. of Rostock ex- 0 0 3 6 9 12 periment. Propagation distance [cm]

1.0 T4: Dissipative Quantum Dynamics 0.8 Reaction centre core complexes can be considered as 0.6 highly efficient nano-machines where excitation energy is trapped and converted via electron transfer (ET) re- 0.4 actions into a charge separated state of polaronic character. The fundamental understanding of photochemical Intensity [arb. u.] 0.2 devices subject to such integrated excitation energy 0 0 3 6 9 12 and charge transfer dynamics is of utmost importance Propagation distance [cm] for, e.g., hot exciton dissociation in organic photovoltaic cells and ultrafast ET in oligothiophene-fullerene heterojunctions. Exciton coupled charge transfer thus Fig. 5: constitutes the basic mechanism for the utilization of Dynamics of three coupled nodes in the quantum solar energy, but its rigorous theoretical description pos- network, simulated via propagation of a photon wave- es persistent challenges that arise in particular for sys- packet in a system of three coupled waveguides. tems of biological relevance where the ‘sluggish’ protein Green and orange curves show tunneling of light environment imposes system-bath memory times of between the two strongly coupled waveguides, and substantial length. We recently developed the non-per- blue shows population in the third, weakly coupled turbative path-integral based MACGIC-iQUAPI method waveguide. The top panel shows dynamics free from [RFi17] for a description of dissipative quantum dynam- decoherence, the bottom panel corresponds to the ics subject to non-Markovian system-bath memory. The case of decoherence. method speeds up simulations dramatically thus showing significant potential for time-resolved biophysics and physical-chemistry applications. separable, and path-entangled photons. Thus, one can investigate how decoherence affects both single- and In [RFi/a] we investigated the impact of vibrational multi-particle excitations and entangled states. To this modes in the spectral density function on population end, a full density matrix theory has been developed for dynamics and the persistence of coherent dynamics in the system composed of an arbitrary number of nodes reaction centre inspired model systems (Fig. 6 (a-b)). It (coupled waveguides). The random phase noise was in- was numerically demonstrated that charge separation troduced by randomly changing the refractive index of in bacterial reaction centres (bRC) appears particularly the waveguides. Two upper (red and green) waveguides robust with respect to intramolecular vibrations even if were strongly coupled to each other, while the third (bot- finite timescales of medium relaxation and charge sep- tom) waveguide was weakly coupled to the other two. aration from coherent non-equilibrium states is account- The theory was developed for single particles and en- ed for (Fig. 6 (c)). tangled two-particle states. The bRC inspired model covers extended, complex dy- When a single-particle was launched into one of the namics ranging from initially coherent oscillatory dynam- waveguides, the wavepacket was found to undergo ics to the incoherent trapping of population within low the expected decoherence, see Fig. 5. Launched into energy charge separated states. The results suggest a single waveguide, the light would oscillate between moderate impact of vibrational modes on ET dynamics the three waveguides, but the oscillations would die out and a decoupling of time-scales of coherent excitation with propagation distance, reflecting decoherence ef- energy and charge transfer dynamics. Our findings sug- fects, see Fig. 5 The single-photon Fock state and the gest an emerging picture where intramolecular vibra- coherent state were found to evolve to the same density tions assure the robustness of optimal ET reactions via matrix. However, the analysis also demonstrated that mediating resonance conditions for optimal, i.e., non-ac- if an entangled state of two identical photons is sent tivated charge transfer. into the network (Fig. 4 right panel), the two identical photons will lose all coherence associated with entan- Further, electron transfer pathways and dynamics were glement but they will not lose the quantum coherence investigated in Drosophila cryptochrome (dCRY) [RFi], associated with their indistinguishability. In essence, all a highly conserved flavoprotein consisting of an N-ter- input states of two identical photons (Fock state, any minal photolyase homology region (PHR) that binds a

33 Own Publications 2018 ff (a) (a)(a) P A (for full titles and list of authors see appendix 1) P B

B A B B ADP18a: D. Ayuso et al.; J. Phys. B 51 (2018) 06LT01/1-7

ADP18b: D. Ayuso et al.; J. Phys. B 51 (2018) 124002/1-13

H B H A ASA18: M. V. Arkhipov et al.; Laser Phys. Lett. 15 (2018) 075003/1-7 (b) (b)(b) E x c BBI18: D. Busto et al.; J. Phys. B 51 (2018) 044002/1-12 i t o n 1 BCD18: S. Beaulieu et al.; Nat. Phys. 14 (2018) 484-489 vibrational

E modes

E e g y xc g i d i

r t

o r BCJ18: R. Y. Bello et al.; Sci. Adv. 4 (2018) eaat3962/1-6 e D n B n on 2

E / or

Energy E BGM18: W. Becker et al.; J. Phys. B 51 (2018) 162002/1- 16 (Topical Review) Acceptor BKl18: W. Becker et al.; Phys. Scripta; https: //doi. Reaction Coordinate Reaction Coordinate org/10.1088/1402-4896/aaecae (2018) 1-24 (c)(c) 1.0 CMH18: C. Cirelli et al.; Nat. Commun. 9 (2018) 955/1-9 0.8 CST18: M. Cerchez et al.; Appl. Phys. Lett. 112 (2018) 0.6 221103/1-6 0.4

Population DJM18: G. Dixit et al.; Phys. Rev. A 98 (2018) 053402/ 0.2 1-6

0 10-2 10-1 100 DSG18: J. K. Dewhurst et al.; Phys. Rev. Appl. 10 (2018) t [ps] 044065/1-8

Fig. 6: EKR18: S. Eckart et al.; Nat. Phys. 14 (2018) 701–704 The bacterial reaction centre (bRC) inspired model system: (a) structural arrangement of Fen18: T. Fennel; Nature 561 (2018) 314-315 bacteriochlorophylls (B) and bacteriopheophytines (H) in the bacterial reaction centre B. viridis. Redox GBH18: A. Gazibegović-Busuladžić et al.; Phys. Rev. A cofactors of the active A-branch and considered in 97 (2018) 043432/1-13 the bRC-inspired model are highlighted with colors, cofactors of the inactive B-branch are indicated in grey GBM18: A. Gazibegović-Busuladžić et al.; Opt. Express (pdb: 1PRC); (b) two exciton states (orange and green) 26 (2018) 12684-12697 are coupled to a bridge state (red) and an acceptor charge transfer (CT) state (blue). A tuning of the HIP18: K.-S. Ho et al.; Sci. Rep. 8 (2018) 10584/1-8 bridge state energy allows to switch from sequential to superexchange regimes of CT. (c) non-equilibrium HMS18: A. Harvey et al.; J. Chem. Phys 149 (2018) dynamics of a bRC inspired three-state model (solid 064104/1-9 −1 lines – vibrational mode frequency ω0 = 0 cm , dashed −1 lines – ω0 = 500 cm ). HWA18: A. Husakou et al.; Phys. Rev. A 97 (2018) 023814/1-6

fl avin adenine dinucleotide (FAD) cofactor, and a C-ter- JDP18: Á. Jiménez-Galán et al.; Nat. Commun. 9 (2018) minal α-helical domain with a variable C-terminal tail 850/1-6 (CTT). dCRY functions as blue-light photoreceptor by synchronizing the circadian clock to the external stimuli JNL18: R. Jones et al.; Phys. Rev. A 97 (2018) 053841/1- of incident sunlight via conformational changes located 13 in the CTT. Dissipative quantum dynamics simulations employing MACGIC-iQUAPI algorithm reveal a branch- JZA18: Á. Jiménez-Galán et al.; Phys. Rev. A 97 (2018) ing of charge separation dynamics in dCRY due to 023409/1-14 subtle balanced energetics within the enzyme. In silico mutations of charged amino acids provide control over KAB18: M. Kübel et al.; J. Phys. B 51 (2018) 134007/1-8 charge transfer directionality thus revealing the role of protein electrostatics in the unknown photore-cep- KSm18a: J. Kaushal et al.; J. Phys. B 51 (2018) tion mechanism which leads to to CTT conformational 174001/1-16 changes upon light absorption of the FAD cofactor.

34 KSm18b: J. Kaushal et al.; J. Phys. B 51 (2018) SPH18: L. Seiffert et al.; J. Phys. B 51 (2018) 134001/1-7 174002/1-15 TBA18: P. Tzenov et al.; New J. Phys. 20 (2018) KSm18c: J. Kaushal et al.; J. Phys. B 51 (2018) 053055/1-10 174003/1-12 VHH18: P. Varytis et al.; Opt. Lett. 43 (2018) 3180/1-4 LAK18: Z. Lécz et al.; Plasma Phys. Control. Fusion 60 (2018) 075012/1-9 VKB18: V. Vaicaitis et al.; J. Phys. B 51 (2018) 045402/1-6

LAn18a: Z. Lécz et al.; J. Opt. Soc. Am. B 35 (2018) WBM18: C. Wolff et al.; Phys. Rev. B 97 (2018) A49-A55 104203/1-14

LAn18b: Z. Lécz, et al.; New J. Phys. 20 (2018) 033010/1-8 in press

MAn18: S. K. Mishra et al.; J. Opt. Soc. Am. B 35 (2018) RFi/a: M. Richter et al.; Faraday Discuss. (2019) DOI: A56-A66 10.1039/C8FD00189H

MBe18a: D. B. Milošević et al.; J. Phys. B 51 (2018) RFi: M. Richter et al.; Ultrafast Phenomena XXI 054001/1-9

MBe18b: R. Mueller, et al.; Phys. Rev. B 98 (2018) 085428/1-7 Other Publications

MHS18: Z. Mašín et al.; J. Phys. B 51 (2018) 134006/1-17 RPM13: M. Richter et al.; New J. Phys. 15.8 (2013): 083012 Mil18a: D. B. Milošević; Phys. Rev. A 97 (2018) 013416/1-8 BCB16: T. Bredtmann et al.; Phys. Rev. A 93 (2016): 021402 Mil18b: D. B. Milošević; Phys. Rev. A 98 (2018) 033405/1-7 BPI16: T. Bredtmann et al.; Phys. Rev. Lett. 117 (2016): 109401. Mil18c: D. B. Milošević; Phys. Rev. A 98 (2018) 053420/1-8 NGS08: T. Nubbemeyer et al.; Phys. Rev. Lett. 101 (2008) 233001 MKS18: M. Moeferdt et al.; Phys. Rev. B 97 (2018) 075431/1-10 RFi17: M. Richter et al.; J. Chem. Phys. 146 (2017) 214101/1-13 MMP18: M. Matthews et al.; Nat. Phys. 14 (2018) 695– 700 ZPI17: H. Zimmermann et al.; Phys. Rev. Lett. 118 (2017): 013003. OBI18: M. Oelschläger et al.; Phys. Rev. A 97 (2018) 062507/1-13 BS11: I. Barth et al.; Phys. Rev. A 84 (2011) 063415

OSm18: A. F. Ordonez et al.; Phys. Rev. A 98 (2018) BS13: I. Barth et al.; Phys. Rev. A 88 (2013) 013401 063428/1-20 Mil16: D. B. Milošević; Phys. Rev. A 93 (2016) 051402(R) PGL18: A. Perez-Leija et al.; npj Quantum Inform. 4 (2018) 45/1-12 HMK16: A. Hartung et al.; Nature Photonics 10 (2016), 526–528 PHG18: E. Pisanty et al.; New J. Phys. 20 (2018) 053036/1-8

PIH18: J.-S. Pae et al.; Phys. Rev. B 98 (2018) 041406/1-4 Invited Talks at International Conferences (for full titles see appendix 2) PLS18: A. Perez-Leija et al.; J. Phys. B 51 (2018) 024002/1-9 A. A. Andreev and S. Ter-Avetisyan; 18th Int. Confer- ence on Laser Optics, ICLO 2018 (St. Petersburg, Rus- PMC18: B. M. Pilles et al.; J. Phys. Chem. A 122 (2018) sia, 2018-06) 4819–4828 A. A. Andreev; Workshop on Theory and Simulation of PWF18: M. Peter et al.; Appl. Phys. B 124 (2018) 83/1-6 Photon-Matter Interaction (Szeged, Hungary, 2018-07)

SBR18: R. E. F. Silva et al.; Nat. Photonics 12 (2018) A. A. Andreev; Int. Conference on Ultrafast Optical Sci- 266–270 ence (UltrafastLight-2018) (Moscow, Russia, 2018-10)

35 D. Ayuso; Quantum frontiers in molecular science (Tellu- M. Richter, 49th Annual Meeting of the APS Division ride, USA, 2018-06) of Atomic, Molecular and Optical Physics (Florida, FL, USA, 2018-05) D. Ayuso; 256th ACS National Meeting & Exposition (Boston, USA, 2018-08) S. Sharma; SPICE Workshop 2018: Ultrafast Spintron- ics: from Fundamentals to Technology (Johannes Gu- D. Ayuso; SILAP 2018 (Toronto, Canada, 2018-12) tenberg Universität Mainz, 2018-10)

W. Becker; 27th Annual Int. Laser Physics Workshop O. Smirnova; Gordon Research Conference ‘Pho-toion- (LPHYS’18) (Nottingham, UK, 2018-07) ization & Photodetachment’ - From Attosec-onds to Na- noseconds: The Chemistry and Physics of Electrons, A. Husakou; Days on Diffraction (St. Petersburg, Rus- Atoms, Molecules, and Light (Galveston, TX, USA, sia, 2018-06) 2018-02)

F. Intravaia; German-BGU (Ben Gurion University) O. Smirnova; PALM Int. School 2018, Attosecond Sci- Workshop on Quantum Technology (Beer Sheva, Israel, ence: from ultrafast sources to applications (Gif-sur- 2018-12) Yvette, France, 2018-03)

M. Ivanov; Symposium on Recollision Physics 2018 O. Smirnova; Workshop “Light field induced dynamics in (Montebello, Quebec, Canada, 2018-05): low dimensional systems” (Universität Duisburg-Essen, M. Ivanov; MURI Mid Infrared Annual Meeting 2018 (Ar- Germany, 2018-04) lington, USA, 2018-05) O. Smirnova; Symposium on Recollision Physics 2018 M. Ivanov, CECAM School: New Computational Meth- (Montebello, Quebec, Canada, 2018-05) ods for Attosecond Molecular Processes (Zaragoza, Spain, 2018-05) O. Smirnova; CECAM School: New Computational Methods for Attosecond Molecular Processes (Zara- M. Ivanov; Gordon Research Conference on Multipho- goza, Spain, 2018-05) ton Processes (Smithfield, RI, USA, 2018-06) O. Smirnova; Int. Symposium on Light Driven Dynam- M. Ivanov; Workshop on atomic physics (Dresden, Ger- ics (LiDy) (East China Normal University, Shanghai, many, 2018-11) China, 2018-11)

Á. Jiménez Galán; QUTIF Workshop 2018 (Hamburg, O. Smirnova; QUTIF-Young Researcher Meeting Quan- Germany, 2018-02) tum Dynamics in Tailored Intense Fields (Berlin, Ger- many, 2018-12) Á. Jiménez Galán; SILAP 2018 (Toronto, Canada, 2018 -12)

Á. Jiménez Galán; XIX Int. Conference ‘Foundations Invited External Talks at Seminars and Collo- & Advances in Nonlinear Science’ and IV Int. Sympo- quia sium ‘Advances in Nonlinear Photonics’ (Minsk, Belar- (for full titles see appendix 2) us, 2018-09) W. Becker, Atomic Molecular and Optical Seminar (Tex- F. Morales, XIX Int. Conference, Foundations & Ad- as AM University, Department of Physics & Astronomy, vances in Nonlinear Science and IV Int. Symposium Ad- USA, 2018-10) vances in Nonlinear Photonics (Minsk, Belarus, 2018- 09) B. P. Fingerhut, Kolloquium der Physikalischen Chemie (Ludwig-Maximilians-Universität München, Germany, S. Patchkovskii; Symposium on Recollision Physics 2018 -11) 2018 (Montebello, Quebec, Canada, 2018-05) B. P. Fingerhut, Seminar Theoretische Chemie (Univer- A. Perez-Leija; Meeting of the Mexican Quantum In- sität Potsdam, 2018-12) formation Division DICU 2018 (Guanajuato, Mexico, 2018-09) S. Sharma, Tutorial (Freie Universität Berlin, 2018-10)

H. Reiss; 10th Asian Symposium on Intense Laser Sci- O. Smirnova, Kolloquium (University of Rostock, Ger- ence (ASCILS10) (American University of Sharjah, many, 2018-05) Sharjah, UAE, 2018-03) O. Smirnova, Student Invited Lecture (Princeton, NJ, H. Reiss; 27th Annual Int. Laser Physics Workshop USA, 2018-11) (LPHYS’18) (Nottingham, UK, 2018-07)

H. Reiss; 27th Annual Int. Laser Physics Workshop (LPHYS’18) (Nottingham, UK, 2018-07)

36 1.2: Ultrafast Laser Physics and Nonlinear Optics

Project coordinators: G. Steinmeyer, U. Griebner, V. Petrov and M. Bock, W. Chen, E. Escoto, T. Feng, L. v. Grafenstein, R. Grunwald, J. Hyyti, M. Jasiulek, M. Mero, T. Nagy, M. Kretschmar, Z. Pan, R. Liao, A. Treffer, L. Wang, Y. Wang, Y. Zhao

1. Overview • Carrier-envelope phase noise and stabilization • Novel nonlinear optical effects The main objective of this project is to develop advanced • Adaptive shaping and propagation of structured sources of ultrashort pulses in the near- and mid-infra- non-diffracting few-cycle wave packets red (IR) wavelength range. To this aim, new laser ge- • Advanced pulse characterization methods ometries and pump sources, special operational modes • Ultrafast singular optics in spectral and temporal do- and pulse-shaping techniques are investigated. A major main with high resolution and high sensitivity. part of the results generated in this project is directly applied for implementing new laser systems for other T2: Power scaling of diode-pumped femtosecond research projects. laser systems beyond Ti:sapphire

In part this project is dedicated to fundamental research on Partly supported by DFG (PE 607/14-1) and Laserlab ultrafast nonlinear optics, carrier-envelope phase effects, JRA ILAT grants (EU) pulse characterization, and beam shaping techniques. Currently, there is a strong trend towards the develop- • Ultrafast lasers/amplifiers based on different dop- ment of CEP-stable mid-infrared sources at wavelengths ant-host combinations for the 1 to 2-µm spectral range >1.5 µm. Such wavelengths are desirable for shorter cut- • Second-order nonlinear frequency conversion for off wavelengths in high-harmonic generation but also for ultrafast systems, especially OPA and OPCPA for driving hard X-ray plasma sources, where presently no down-conversion to longer wavelengths in the near- CEP control is required. A great deal of the activities is and mid-IR devoted to exploring components for such systems which • Few-cycle high power, high repetition rate mid-IR OP- includes characterization and testing of various laser and CPA systemss. nonlinear materials in diverse operational regimes. One of the large scale OPCPA systems was designed to deliv- Collaboration partners: M. Guina (ORC, Tampere, Fin- er two ultrafast, optically synchronized pulse trains at 1.5 land), G. Genty (TUT, Tampere, Finland), A. Demircan, and 3.1 µm with average powers well above 10 W in each U. Morgner (Leibniz-Universität Hannover, Germany), beam, constituting an unprecedented total average power C. Brée (Weierstraß-Institut, Berlin, Germany), R. Tre- at a repetition rate of 100 kHz. The system, completed in bino (Georgiatech, Atlanta, GA, USA), A. Fry, (SLAC, 2018, was successfully tested in strong-field experiments USA), B. Hofmann (TU Chemnitz, Germany), Y. Song in the gas phase. The work on a second large scale OP- (Tianjin University, China), W. Hänsel and R. Holzwarth CPA system targeting the 5-µm wavelength range and (Menlo Systems, Germany), U. Wallrabe (IMTEK, Uni- aiming at sub-100 fs, 1 kHz pulses, has continued in 2018 versity Freiburg, Germany), metrolux GmbH (Göttingen, with the completion of the mid-IR parametric amplifier Germany), J. Jahns (FernUniversität, Hagen, Germany), chain delivering unprecedented output parameters. W. Seeber (Otto Schott Institute, FSU Jena, Germany), E. McGlynn (School of Physics, Dublin City University, The work on spatio-temporal shaping and characteriza- Dublin, Ireland), F. Güell (University Barcelona, Spain), tion of ultrashort wave packets was successfully con- HoloEye Photonics AG (Berlin, Germany), F. Diaz (Uni- tinued. New adaptive components for ultrashort pulses versity Tarragona, Spain), P. Fuhrberg (LISA laser OHG, were developed in collaboration with microsystem ex- Germany), H. Zhang (Shandong University, China), F. perts. Fundamental research on ultrafast singular op- Rotermund (Ajou University, Korea), A. Agnesi (Pavia tics, in particular on the propagation of spectral anom- University, Italy), J. Liu (Qindao University, China), B. alies, was performed. The classical Talbot self-imaging Kanngießer (TU Berlin, Germany), L. Isaenko (DTIM effect was extended to rotation-encoded arrays of orbit- Novosibirsk, Russia), V. Pasiskevicius, (KTH, Stock- al angular momentum pulses. holm, Sweden), P. Schunemann (BAE Systems, Nash- ua, USA), V. Badikov (HTL, Krasnodar, Russia), K. Kato (Chitose, Japan), l. Buchvarov (Sofia University, Bulgar- ia), M. Ebrahim-Zadeh (ICFO, Barcelona, Spain), M. 2. Topics and collaborations Eichhorn (ISL, France), V. Panyutin (Kuban State Uni- versity, Russia), G. Arisholm (FFI, Norway), Z. Heiner At present the project is organized in two topics: (SALSA, HU Berlin, Germany), P. Simon (Laser-Labo- ratorium Göttingen, Germany), R. Lopez-Martens (LOA, T1: Ultrafast nonlinear optics France), H. Crespo (University of Porto, Portugal), J. Limpert (Friedrich-Schiller-Universität Jena, Germany), Partly supported by DFG (STE 762/11-1, GR 1782/14-1 S. Hädrich (Active Fiber Systems, Germany). and GR 11782/14-2), IBB ProFIT 10164801 OptoScope, and CSC/DAAD

37 3. Results in 2018 phase elements enables to study specific self-imaging phenomena with broadband ultrashort pulses. T1: Ultrafast nonlinear optics Previously, we demonstrated temporal self-imaging of few-cycle pulses for arrays of non-diffracting Bes- Talbot self-imaging of ultrafast OAM pulses and Gouy sel-like needle structure. Furthermore, the Gouy rota- rotation echoes tion of spectral anomalies around a singularity [LTB18] was revealed by spectral moments and meta-moments Classical Talbot self-imaging describes the recon- [LTBa]. In recent experiments, we studied the com- struction of light fields in periodic amplitude or phase bination of both phenomena and further extended the patterns by constructive interference of diffracted Talbot self-imaging approach to arrays of polychromat- light. This allows for transferring periodicity informa- ic beams each carrying an orbital angular momentum tion from near-field to far-field and to coherently cou- (OAM). This enhances the number of free parameters ple optical beams. The availability of low-dispersion by particular vortex properties like topological charge and sign of rotation. As we have shown theoretically and experimentally, Talbot images can be significantly altered by encoding non-uniform configurations (e.g. super-lattices) into maps of rotation signs. In a first experimental verification, we compared self-imaging for two simple cases with each other: (a) co-rotating arrays (i.e., all wavefronts rotate in the same direction), and (b) counter-rotating arrays with checkerboard-pattern (i.e., neighboring sub-beams rotate in opposite directions). Experiments were performed with Ti:sapphire laser pulses (pulse duration 120 fs, FWHM bandwidth 10 nm) [LTBb, LTBc]. Fig. 1 schematically shows the expected self-imaging of spectral Gouy rotation, i.e., Fig. 1: the twist of blue- and red-shifted regions around phase Principle of spatio-spectral self-imaging of poly- singularities. chromatic orbital angular momentum (OAM) pulses. Along the propagation axis z, 2D maps of spectral Intensity propagation was recorded with a sensitive EM- moments M(x,y) are determined. A spiral grating CCD camera. The different sense of rotation of adjacent array (SGA) generates a zone with two extremal beams leads to single and split maxima in the first half spectral regions (red and blue dots) with a center Talbot plane (k = 1/2). Spectral maps were detected with distance z0. Spectral Guoy rotation (SRG), i.e. a a grating spectrometer by scanning the magnified field twist of these regions around the singularities, is of interest with a fiber. For co-rotating OAM-pulses, a periodically reconstructed by Talbot self-imaging (SI) spectral Gouy rotation was found with sufficient spectral resulting in “SGR echoes” [LTBb]. contrast (Fig. 2) whereas it was strongly distorted for counter-rotating pulses.

Fig. 2: 0.8 0.8 Spectral Gouy rotation echo for co-rotating OAM pulses indicated by mapping spectral 0 0 centers of gravity (red: minima, blue: maxima) for different distances -0.8 -0.8 (from left to right: -0.8 0 0.8 -0.8 0 0.8 6.21, 6.30, 6.40, and 6.50 mm; y [µm ] FOV: 1.9 x 1.9 µm2) 0.8 0.8 around the first Talbot plane (k = 1).

0 0

-0.8 -0.8

-0.8 0 0.8 -0.8 0 0.8 x [µm]

38 The findings demonstrate that pulse arrays with OAM into an active and a passive f-to-2f interferometer branch. encoded wavefronts can be tailored via topologically Both branches employ 10 mm long periodically-poled sensitive interference. The additional degree of freedom lithium niobate (PPLN) crystals for frequency doubling enables to distinguish between individual sub-beams of and avalanche photodiodes for detection of the RF beat arrays and to generalize self-imaging of coherent light signal. Given that green light is absorbed in the Yb:fiber fields. used as optical amplifier, we resort to a Mach-Zehnder interferometer in the active f-to-2f interferometer. Long Active f-to-2f interferometer for advanced carrier-enve- pass filters are used as beam splitter and combiners in lope phase stabilization the interferometer, and the optical amplifier is constructed from a 45 cm long segment of ytterbium-doped fiber. The Carrier envelope phase (CEP) stabilization has proven amplified f signal is recombined with the 2f component an indispensable tool in attosecond science and pre- and focused into the PPLN crystal for frequency dou- cision frequency metrology. While fully CEP stabilized bling. For CEP stabilization, we use commercial servo mode-locked fiber lasers and Ti:sapphire lasers have electronics (Menlo XPS800). become commercially available in the last decade, it seems safe to say that CEP stabilization and all-optical In our experiments, the CEO signal in the passive f-to-2f frequency synthesis are still far from a general applica- interferometer exhibits an SNR of about 40 dB. After op- bility. For example, a particularly difficult problem is the timizing the pump power of the fiber amplifier, the active CEP stabilization of high-repetition rate lasers with their f-to-2f interferometer provides a CEO signal with almost low pulse energies. Measurement of the CEP involves 20 dB SNR improvement, reaching nearly 60 dB. Using two cascaded nonlinearities, namely a supercontinu- the active f-to-2f interferometer for CEP stabilization, the um process for spectral broadening and subsequent residual phase noise was measured for 20 s at 5 MSa/s second-harmonic generation of the infrared tail of the sampling. The in-loop signal exhibits a Gaussian distri- broadened spectrum. Even when starting with nano- bution with an rms value of 10 mrad (cf. Fig. 4). In the joule pulses from Ti:sapphire oscillators, there often only shot-noise dominated region above 1 MHz, the resid- remain a few photons in the optical heterodyne signal. ual noise levels are comparable in the in-loop and the When this number falls significantly below 10 detected out-of-loop signal. Integrating from 2.5 MHz to 1 Hz, we photons per pulse it becomes impossible to stabilize the determine a residual phase jitter of the out-of-loop signal CEP of the laser. At first sight, it appears impossible to of about 15 mrad, which corresponds to a timing jitter overcome this limitation at low pulse energies as it is im- of 6 as between carrier and envelope. This constitutes posed by shot noise in the detection, i.e., neither optical a record-breaking value, i.e., the lowest CEP jitter ever nor electronic amplification can restore a high signal-to- reported for a laser oscillator. noise ratio. However, placing an optical amplifier in between the two nonlinearities may offer a viable option to The most important finding of our study is certainly the overcome shot noise limitation because the signal has absence of deterioration effects due to amplifier noise. not yet degraded to the single-photon level at this inter- Amplified spontaneous emission in the Yb:fiber isex- mediate step. As one may certainly be skeptical whether pected to increase the amplitude noise in the f beam, yet or not additional noise contributions in the optical ampli- this does only marginally affect the CEP signal, which is fier thwart the potential improvement, we experimentally encoded in the phase. In fact, it is Schawlow-Townes verified our novel idea of an active f-to-2f interferom- noise that is ultimately limiting us here, and this is ex- eter with a Ti:sapphire laser oscillator operating at an pected to be too weak to cause any measurable effect. 85 MHz repetition rate. We expect that our active f-2f scheme can be trans- ferred to other types of lasers, including amplified sys- The octave supercontinuum is obtained by launching tems. Moreover, using optical amplification inside the 65 mW from this laser into a 1 cm long photonic crystal fi- CEP detection scheme may prove to render currently ber (Fig. 3). The output from this fiber is then equally split unlockable lasers CEP stable.

Fig. 3: AL AL Experimental setup. Active servo MS F PD f-to-2f interferometer is in Ti:S oscillator frep ÷ 4 the red shaded box, passive reference in the blue AL AL BPF DM C ﬁber ampliﬁer C DM PPLN APD shaded one. AL: aspheric BS lens; MSF: micro-structure fCEO mixer fiber; BS: beam splitter; M: mirror; DM: dichroic mir- a ctive f -2f ror; C: collimator; PPLN: passive f -2f periodically poled lithium M AL AL BPF niobate crystal; BPF: PPLN APD mixer M DOS bandpass filter; APD: ava- DM fCEO lanche photo-diode; PD: photo-diode; DOS: digital oscilloscope.

39 10 0

Hz] -2 √ 10

PND. [rad/ 10-4

10-6 40

20 IPN [mrad]

0 100m 1 10 100 1k 10k 100k 1M Frequency [Hz]

Fig. 4: Phase noise analysis [LTF]. Phase noise spectra (PND) using the active f-to-2f interferometer for feedback stabilization and integrated phase noise (IPN). Red traces: IL signals. Blue traces: OOL signals. Gray trace: background noise.

Fig. 5: 1 1 (a) (b) D-scan measurement of a 4 fs pulse 1.5 1.5 using XPW and 2 2 SHG nonlinearities. In the upper row 2.5 2.5 the XPW-based, in Glass ins. [mm] Glass ins. [mm]

Glass ins. [mm] the middle row the 3 3 SHG-based measurement is shown 3.5 3.5 500 600 700 800 900 1000 500 600 700 800 900 1000 whereas on the left Wavelength [nm] Wavelength [nm] side ((a) and (c)) are 1 the measured trac- 1 (c) (d) es, on the right side 1.5 1.5 ((b) and (d)) are the retrieved traces. 2 2 The retrieved pulse shapes are shown 2.5 2.5 in (e), while the

Glass ins. [mm] spectral intensity Glass ins. [mm] 3 3 and phase in (f) 3.5 300 340 380 420 3.5 300 340 380 420 (SHG: dashed red; Wavelength [nm] Wavelength [nm] XPW: solid blue).

(e) (f) 12 1 1

0.8 0.8 6

0.6 0.6 0

0.4 0.4 -6 Phase [rad]

Intensity [a.u.] 0.2 0.2

Spectral power [a.u.] -12 0 0 -40 -20 0 20 40 500 600 700 800 900 1000 Time [fs] Wavelength [nm]

40 Dispersion scan for the characterization of near sin- self-phase modulation inside the XPW crystal were also gle-cycle pulses investigated both experimentally and theoretically. We fi nd that crystal lengths of up to 200 µm can be used for The characterization of light pulses near the single-cycle the characterization of 4 fs pulses with high fi delity. This limit is a challenging task where only a few options are is surprising as the propagation through such a long available. One of the best choices is dispersion scan crystal results in a dispersive broadening to more than (d-scan) with its very simple setup based on a single- 6 fs duration [TOV]. beam geometry. Originally, d-scan incorporates second harmonic generation (SHG) as nonlinearity, prone to Another important application of the XPW d-scan phase-matching limitations. Recently, we introduced a technique is the characterization of ultrashort pulses d-scan arrangement using cross-polarized wave (XPW) in the deep UV spectral range. In order to demonstrate generation instead of SHG. As a degenerate four- the capability of the technique we generate slightly wave mixing process XPW does not involve frequency negatively chirped broadband DUV pulses by mixing conversion, it is free from phase-matching issues. This broadband negatively chirped NIR pulses with narrow- gives XPW d-scan a great potential for handling pulses band second harmonic signal in an ultra-thin BBO with over-octave spanning spectrum even at diffi cult crystal. The UV pulse characterization experiments will wavelength ranges such as deep-UV. be continued in 2019.

In cooperation with colleagues from France, Portugal T2: Power scaling of diode-pumped femtosecond and Germany we characterized 4 fs long 1.5-cycle laser systems beyond Ti:sapphire NIR pulses from a high-energy hollow fi ber both with SHG and XPW-based d-scan arrangements. Sub-100 fs bulk solid-state lasers in the 2 µm spectral The pulses from the hollow fi ber are sent through range a motorized wedge pair and a subsequent chirped mirror compressor. By varying the fused silica Exploring novel Tm-doped laser crystals in connection thickness inserted into the beam path, the chirp of the with an advanced dispersion management, the shortest pulses can be varied continuously around the optimal pulses from bulk solid-state oscillators in the 2-μm compression. After the compressor the pulses are spectral range were demonstrated. Employing single- sent either into the SHG-based or into the XPW-based walled carbon nanotubes (SWCNTs) as a saturable detection setup. For the SHG detection a commercial absorber (SA) and chirped mirrors for dispersion device from Sphere Photonics incorporating a 5 µm management 78 fs pulses were achieved with the thick BBO crystal is used. In the XPW arm the linear disordered crystal Tm:CLNGG [WZP18]. polarization of the incoming beam is fi rst enhanced by using two subsequent Brewster-angled refl ections Ca3Nb1.5Ga3.5O12 (shortly CNGG) and and then focused by a spherical mirror onto the Ca3Li0.275Nb1.775Ga2.95O12 (shortly CLNGG) are typical surface of a thin BaF2 crystal, where the nonlinear disordered crystals which belong to the cubic signal with perpendicular polarization is generated. multicomponent garnets. They have proved to be The XPW signal is then discriminated by a Glan- excellent laser host materials for the generation of Laser polarizer which suppresses the incoming pump ultrashort pulses around 1 μm due to the inhomogeneous beam by high extinction ratio. The spectrum of the spectral line broadening of the Yb3+ dopant. This fi ltered signal is then recorded in function ofthe stimulated extension of this research to the 2-μm wedge insertion by a calibrated spectrometer having a spectral range with Tm3+-doping. fl at broadband spectral response. The recorded traces are evaluated by a differential evolutionary algorithm. A 3 at.% Tm:CLNGG crystal with 3.1-mm length along Both SHG and XPW measurements are shown in the (111) crystallographic axis and 3×3 mm2 aperture Fig. 5 exhibiting excellent consistency. By applying was polished to laser grade (inset of Fig. 6). An X-shape a series of BaF2 crystals of different thicknesses cavity was used as shown in Fig. 6. The SWCNT-SA propagation effects such as material dispersion and was placed in one cavity waist of the resonator under

Fig. 6: Scheme of the mode- locked Tm:CLNGG

laser (L: lens; M1-M2: dichroic folding

mirrors; CM1-CM4: chirped mirrors; OC: output coupler). Inset: Photo of the Tm:CLNGG crystal.

41 (a) (c) (d) 4 4 1070 1.0 3 1.0 3 1010 ] ] 950 2 2 Wavelength [nm ] Wavelength -150 0 150 (b) Delay [fs] 0.5 1 0.5 1 Phase [rad ] Phase [rad ]

1070 Intensity [a.u. Intensity [a.u. 0 0 1010

950 0.0 -1 0.0 -1 -200 -100 0 100 200 1900 1950 2000 2015 2100 2150 Wavelength [nm ] Wavelength -150 0 150 Time [fs] Wavelength [nm] Delay [fs]

Fig. 7: SHG-FROG characterization: (a) Measured and (b) retrieved SHG-FROG traces; (c) retrieved pulse intensity / phase (black solid line / red dashed line); Fourier-limited pulse shape calculated from the retrieved spectral profile (blue dash- dotted line); and (d) retrieved spectral intensity / phase (black solid line / red dashed line) and directly measured spectrum (blue dash-dotted line).

the Brewster angle between two curved chirped mirrors with a FROG error of only 0.002. The derived tem- CM1 and CM2. In the other cavity arm, two plane chirped poral and spectral intensity and phase profiles are mirrors, CM3 and CM4, were employed for additional shown in Figs. 7(c) and (d). A pulse duration of 78 fs intracavity dispersion compensation permitting (FWHM) was obtained with a spectral bandwidth of variation of the number of bounces. All chirped mirrors 58 nm which was in perfect agreement with the di- CM1-CM4 provide a group delay dispersion, GDD = rectly measured optical spectrum. The spectral phase −125 fs2 per bounce. Shortest pulses were obtained indicates that the residual chirp is almost negligible. at 2017 nm for a total intracavity GDD of ～ −1780 fs2 Since the Fourier-limited pulse duration is ~74 fs, per round trip, obtained by a total of 11 bounces on the see blue dash-dotted line in Fig. 7(c), no additional chirped mirrors, as shown in Fig. 6, taking into account extra-cavity pulse compression was attempted. To the contribution of the 3.1-mm thick crystal (−21.5 fs2/ verify the stability, radio frequency spectra were re- mm) and the 1-mm thick fused silica substrate of the corded in different span ranges. The fundamental SWCNT-SA (−104.3 fs2/mm). The output coupler used beat note at 86.26 MHz displays an extinction ratio had a transmission of 0.5 %. of 76 dBc above carrier and the harmonic beat notes show almost a constant extinction ratio. To the best of Self-starting and stable steady-state mode-locking our knowledge, these are the shortest laser oscillator was achieved for daily operation. The average out- pulses in the 2-μm spectral range obtained with a bulk put power amounted to 54 mW at a repetition rate of crystal as a gain medium. 86 MHz. The pulses were characterized by the second-harmonic generation frequency-resolved opti- 100 kHz OPCPA at 1.55 µm/3.1 µm cal gating (SHG-FROG). Figures 7(a) and (b) show the measured/retrieved FROG traces on a 128×128 The Leibniz SAW project launched in 2012 has been grid size. Due to the rather symmetric and straight- devoted to the development of a high average power forward FROG trace, the retrieval was almost perfect OPCPA system pumped with 1.03 µm pulses at a rep-

Fig. 8: Scheme of the 100 kHz 1.55 µm/3.1 µm OPCPA system. SHG, second-harmonic generation; WLC, white-light continuum generation; DFG, difference-frequency generation; OPA, optical parametric amplifier; PPLN, periodically

poled LiNbO3; KTA, KTiO-

AsO4; CM, chirped mirrors; ADC, angular dispersion compensation; Si, silicon window.

42 1700 850 850 1700 1600 800 800 1600 1500 1500 750 750 1400 1400 -200 -100 0 100 200 Wavelength [nm ] Wavelength [nm ] Wavelength -200 -100 0 100 200 [nm ] Wavelength -200 -100 0 100 200 [nm ] Wavelength -200 -100 0 100 200 Delay [fs] Delay [fs] Delay [fs] Delay [fs] ] ] ] ] Phase [rad ] Phase [rad ] Phase [rad ] Phase [rad ] Intensity [arb. units Intensity [arb. units Intensity [arb. units Intensity [arb. units -200 -100 0 100 200 1400 1500 1600 1700 -200 -100 0 100 200 2800 3000 3200 3400 Time [fs] (a) Wavelength [nm] (b) Time [fs] Wavelength [nm]

Fig. 9: SHG-FROG characterization: Measured and retrieved SHG-FROG traces (upper panels); reconstructed temporal and spectral intensity and phase (lower panels) of the simultaneously available, optically synchronized 1.55 µm signal (a) and 3.1 µm (idler pulses). etition rate of 100 kHz, see Fig. 8. The full, three-stage scale the peak power of the OPCPA system to several system was completed in 2018 delivering an unprece- 10 GW and to implement it as driver for hard x-ray dented total average power in the near-IR signal and generation. mid-IR idler beams of 66 and 55.5 W before and after chirp compensation, respectively. Despite the non- The setup of the midwave-IR (MWIR) OPCPA source collinear geometry, both signal and idler beams were is described in [BGG18]. A 3-color front-end based on available for experiments: a 430 μJ, 51 fs, CEP-stable a femtosecond Er:fiber master oscillator (nrep = 40 MHz) beam at 1.55 μm and a 125 μJ, 73 fs beam at 3.1 μm seeds the 2-µm pump channel and the DFG produced [MHP18], cf. Fig. 9. The generation of high-quality mid- at 3.5 µm. Figure 10 shows the output performance of IR idler pulses was achieved by implementing a simple the 2-µm Ho:YLF chirped pulse amplifier (CPA) pump. angular dispersion compensation scheme based on a It delivers uncompressed pulses with 55 mJ energy at reflection grating and a spherical reflector. The open- nrep = 1 kHz. Due to gain narrowing in the amplifier chain, loop CEP jitter of the 1.55 µm pulse train at the 9 W the pulse duration and the emission bandwidth are reduced level was characterized by f-2f interferometry and was to 250 ps and 2.5 nm (FWHM), respectively (insets Fig. estimated to be ~900 mrad on a single-shot basis. Part 10a). The spectrum is well fitted by a Gaussian shape of the 1.55 µm beam was used in strong-field ionization which supports a ~2.2 ps Fourier-transform limited (FTL) experiments on argon utilizing a reaction microscope pulse duration. So far, the pulse energy for compression detector, and the low RMS fluctuation in the rate of Ar+ was limited to ~26 mJ for damage reasons. Applying a generation corroborated the long-term power and in- new grating compressor, the full pulse energy is now tensity stability of the OPCPA system. employed, resulting in compressed pulses with 45 mJ energy and an excellent pulse-to-pulse stability of An upgrade of the commercial Yb-fiber front-end pump <0.3 % rms. The recorded autocorrelation trace for the laser provided an opportunity for pumping the first two compressed pulses exhibits a FWHM of 4.9 ps (Fig. 10b). OPCPA stages directly from the Yb-fiber laser instead The estimated B-integral of the Ho:YLF CPA has a value of the high-power Yb:YAG innoslab laser amplifier and of ~p rad. The impact of the accumulated nonlinear resulted in a dramatically enhanced stability of various phase on the temporal pulse shape is simulated by laser pulse parameters. The new open-loop single- adding it to the spectral phase of the FTL pulse. The shot CEP jitter at the few W level is ~500 mrad. best match of the simulated to the measured ACF is shown in Fig. 10b. The retrieved pulse shape from this In the near future, the 1.55 μm output of this unique simulation reveals that the main pulse is accompanied system will serve as the pump of a high-flux soft-x-ray by two weak satellites delayed by 8 ps. The resulting source with a spectrum reaching the water window at duration of the main pulse is 2.8 ps (FWHM) with an ~300 eV, while the 3.1 μm beam will provide optically estimated energy content of 77 %, translating into a synchronized driver pulses for studying strong-field remarkable peak power of 10 GW. processes. The 3.5 µm pulses with a duration of 25 fs, covering 1 kHz OPCPA at 5 µm >700 nm spectral bandwidth (FWHM), are phase-only shaped by a MWIR spatial light modulator (SLM), The second SAW project launched in 2014 aims at the stretched to 3 ps and then delivered to the optical development of a high energy (>1 mJ) OPCPA system parametric amplifier (OPA) as signal. The SLM (BNS), at a repetition rate nrep = 1 kHz with sub-100 fs pulses manufactured for the 2 to 7 μm range, is based on a at 5 µm. In 2018 the main activities were devoted to 512x512-pixel liquid crystal (LC) array with a pixel size

43 (a) (b) (a) 6600 Ho:YLF CPA; rms < 0.3% (b) 11.0.0

) measured ACF FWHMACF = 4.9 ps simulated ACF 5500 0.8 r m . 0.8 ( m J ) ) .

1.0 o ) 1.0 . y ACF τ = 250 ps r m

40 ( n 40 o

r m uncompr. r g l o

( n 0.6

e 0.6 a l ( n 2.5 nm n a n y 0.5 n 3300 t 0.5 e i g g i s n - s 00.4.4 e - s i s e t G l

2200 n I G S H Intensity [norm.] 0.0 0.0 Pulse energy [mJ] P u 2048 2051 2054 -400 0 400 SHG-signal [norm.] SHG-signal [norm.] 1100 S H 00.2.2 WavelengthWavelength [nm(nm)] TimeTime ddelayelay ( p[ps]s) 00 00.0.0 0 1100 2020 3300 4400 5050 6600 --4040 - -2020 00 2020 4400 TTimeime [min](min) TTimeime [ps](ps)

Fig. 10: Ho:YLF CPA amplifi er performance at 1 kHz repetition rate. (a) Pulse energy and long-term stability, Insets: optical spectrum and autocorrelation trace (ACF) of the uncompressed pulse; (b) ACF of the compressed pulses, measured and simulated.

1.0 1.0 8 (a(a)) measured calc. from 3 µm signal (b(b)) ) 6 . u y .

t 4 s i r b

n 2 ( a e t l n a 0 i 0.5 0.5 n --900900 -450-450 0 445050 990000 g 8 r m . - S i o ACFFWHM = 96 fs

G 6 N Norm. intensity τFWHM = 68 fs SHG-Signal [arb. u.] 4 S H 4 2 00.0.0 0 44000000 44500500 55000000 55500500 66000000 -200-200 --150150 - -100100 --5050 0 5500 1 10000 115050 220000 WWavelengthavelengt h[nm(n]m) TimeTimedel adelayy (fs [fs) ]

Fig. 11: Characterization of the 5 µm idler pulses. (a) Measured and calculated spectrum (The latter is based on the signal spectrum after the 2nd stage.); (b) Measured interferometric autocorrelation (two scan ranges).

of 37.5 µm. The refl ective SLM is implemented in a on the LC array. The high frequency modulation in the 4-f confi guration using a sapphire prism as dispersive red wing of the spectrum is associated with atmospheric element. The setup provides a throughput of 30 %, absorption. Measured interferometric autocorrelation much higher than the competing solution based on traces of the compressed idler pulses are presented in AOPDFs (<10 %). The maximum phase correction Fig. 11b for two temporal windows. From this data, the stroke attainable is ~3p at 3 µm and the spectral intensity autocorrelation trace was extracted by Fourier resolution of our pulse shaper setup is 10 nm [BGG18]. fi ltering. Best fi t to the data was achieved assuming a For stretching of the signal and compression of the idler Gaussian-pulse shape and a duration of 68 fs for the pulses CaF2 crystals are used. central pulse (Fig. 11b, bottom). The accompanying weak satellites (Fig. 11b, top) are related to the above The OPA consists of 3 stages using ZnGeP2. Employing described modulations in the spectrum and carry about 37 mJ of pump energy in the third stage (collinear 20 % of the energy. In consequence, the estimated geometry), idler pules with 3.1 mJ are generated around energy in the main peak amounts to 2.5 mJ, resulting 5 µm with nrep = 1 kHz. Figure 11a shows the idler spectrum in a peak power of 32 GW. The beam profi le is nearly after the third stage and the expected idler spectrum. diffraction-limited with a noticeable stability of the The latter is calculated based on the measured signal recompressed pulses (rms: <1.0 %). spectrum after the second stage. A ~800 nm bandwidth (FWHM), centered at 5.0 µm is achieved, supporting a The generated multi-millijoule 5-µm pulses with a FTL pulse duration of ~50 fs. The dip in the spectrum duration corresponding to only fi ve optical cycles results at 5.2 µm is result of an absorption band of the SLM- in a peak power of 32 GW which represents the highest LCs at 3.4 µm, the low frequency structure to diffraction achieved for OPCPAs beyond 4 µm so far.

44 In 2019, besides further scaling of the MWIR pulse energy, KUO18: K. Kato et al.; SPIE Proc. 10516 (2018) the focus will be the application of the system as driver 105161D/1-7 for hard x-ray generation. LBS18a: P. Loiko et al.; SPIE Proc. 10511 (2018) 105110B/1-8

LBS18b: P. Loiko et al.; Beilstein J. Nanotechnol. 9 Own Publications 2018 ff (2018) 2730–2740 (for full titles and list of authors see appendix 1) LBS18c: P. Loiko et al.; Opt. Mat. Exp. 8 (2018) 1723- BGG18: M. Bock et al.; J. Opt. Soc. Am. B 35 (2018) 1732 C18-C24 LKM18: P. Loiko et al.; IEEE J. Sel. Top. Quantum Elec- BSG18b: A. A. Boyko et al.; Opt. Mat. Exp. 8 (2018) tron. 24 (2018) 1600713/1-13 549-554 LSM18: P. Loiko et al.; SPIE Proc. 10511 (2018) CKE18: B.-H. Chen et al.; Opt. Exp. 26 (2018) 3861- 105111V/1-9 3869 LSS18: P. Loiko et al.; Opt. Mat. Exp. 8 (2018) 2803- CKO18: H. Cao et al.; Laser Phys. Lett. 15 (2018) 2814 045003/1-8 LTB18: M. Liebmann et al.; SPIE Proc. 10549 (2018) CNB18: B.-H. Chen et al.; Opt. Lett. 43 (2018) 1742- 105490F/1-7 1745 LWS18: P. Loiko et al.; J. Alloys Compounds 763 (2018) CTK18: H. Cao et al.; Opt. Exp. 26 (2018) 7516-7527 581-591

ETN18: E. Escoto et al.; J. Opt. Soc. Am. B 35 (2018) MBe18b: R. Mueller et al.; Phys. Rev. B 98 (2018) 8-19 085428/1-7

FRR18: T. Feng et al. Appl. Phys. Lett. 112 (2018) MHP18: M. Mero et al.; Opt. Lett. 43 (2018) 5246-5249 24110/1-4 MLL18a: X. Mateos et al.; Opt. Exp. 26 (2018) 9011- GBG18: L. von Grafenstein et al.; IEEE J. Sel. Top. 9016 Quantum Electron. 24 (2018) 3000213 MLL18b: X. Mateos et al.; Opt. Mat. Exp. 8 (2018) 684- GGB18: U. Griebner et al.; SPIE Proc. 10713 (2018) 690 107130W/1-4 MLL18c: X. Mateos et al.; SPIE Proc. 10713 (2018) GLL18: M. Gross et al.; J. Phys. Conf. Ser. 1067 (2018) 107130J/1-8 042012/1-6 NCJ18: R. S. Nagymihaly et al.; J. Opt. Soc. Am. B 35 HPM18: J. Hyyti et al.; J. Phys. D 51 (2018) 105306/1-11 (2018) A1-A5

HPS18: Z. Heiner et al.; Opt. Exp. 26 (2018) 25793- NSG18: M. Närhi et al.; J. Opt. Soc. Am. B 35 (2018) 25804 140-145

HSR18: A. Härkönen et al.; Opt. Lett. 43 (2018) 3353- PBR18: S. Popien et al.; Opt. Eng. 57 (2018) 111802/1-7 3356 PDL18: Z. Pan et al.; Cryst. Eng. Comm. 20 (2018) JLS18: W. Jing et al.; J. Luminesc. 203 (2018) 145-151 3388-3395

KLR18a: E. Kifle et al.; Photon. Res. 6 (2018) 971-980 PKa18: V. Pajer et al.; Laser Phys. Lett. 15 (2018) 095402/1-5 KLR18b: E. Kifle et al.; Opt. Exp. 26 (2018) 30826- 30836 PSK18: Z. Pan et al.; Opt. Mat. Exp. 8 (2018) 2287-2299

KMB18a: K. Kato et al.; Appl. Opt. 57 (2018) 2935-2938 PWZ18a: Z. Pan et al.; Photon. Res. 6 (2018) 800-804

KMB18b: K. Kato et al.; Appl. Opt. 57 (2018) 7440-7443 PWZ18b: Z. Pan et al.; Opt. Lett. 43 (2018) 5154-5157

KML18: E. Kifle et al.; Opt. Exp. 26 (2018) 4961-4966 SIR18: L. Shi et al.; Phys. Rev. Appl. 9 (2018) 024001/1-9

KMR18: E. Kifle et al.; SPIE Proc. 10511 (2018) 1-7 SLJ18: J. M. Serres et al.; Opt. Lett. 43 (2018) 218-221

45 TRS18: H. Tian et al.; Opt. Lett. 43 (2018) 3108-3111 V. Petrov; The 26th Annual International Conference on Advanced Laser Technologies, ALT’18, (Tarragona, UPO18: N. Umemura et al.; SPIE Proc. 10516 (2018) Spain, 2018-09) 1051619/1-6 G. Steinmeyer; SPIE Photonics West (San Francisco, WJL18: Y. Wang et al.; Opt. Exp. 26 (2018) 10299- CA, USA, 2018-01) 10304 G. Steinmeyer; AT-RASC 2018 (Maspalomas, Gran Ca- WZP18: Y. Wang et al.; Opt. Lett. 43 (2018) 4268-4271 naria, Spain, 2018-05)

YMK18: F. Yesudas et al.; J. Chem. Phys. 148 (2018) G. Steinmeyer; CLEO 2018 (San Jose, CA, USA, 2018- 104702/1-8 05)

ZLM18: X. Zhang et al.; J. Luminesc. 197 (2018) 90-97 G. Steinmeyer; COFIL 2018 (Geneva, Switzerland, 2018-06) ZLS18: X. Zhang et al.; Appl. Opt. 57 (2018) 8236-8241 G. Steinmeyer; 27th Annual International Laser Physics ZSL18: L. Zhang et al.; J. of Luminesc. 203 (2018) 676- Workshop (Nottingham, UK, 2018-07) 682

ZWZ18: Y. Zhao et al.; Opt. Lett. 43 (2018) 915-918

ZYC18: B. Zhao et al.; Opt. Mat. Exp. 8 (2018) 493-502

in press

KCB: W. Kim et al.; Opt. Express

KZM: M. Kowalczyk et al.; Opt. Express

KUI: K. Kato et al.; Appl. Opt.

LTBa: M. Liebmann et al.; Ultrafast Phenomena XXI

LTBb: M. Liebmann et al.; Opt. Lett.

LTF: R. Liao et al.; Opt. Lett.

TOV: A. Tajalli et al.; IEEE J. Sel. Top. Quantum Elec- tron.

ZWC: Y. Zhao et al.; Opt. Express

Invited Talks at International Conferences (for full titles see appendix 2) U. Griebner; Pacific Rim Laser Damage (Yokohama, Ja- pan, 2018-04)

U. Griebner; Laser Optics (St. Petersburg, Russia, 2018-06)

U. Griebner; Advanced Laser Technology (Tarragona, Spain, 2018-09)

V. Petrov; Pacific Rim Laser Damage (Yokohama, Ja- pan, 2018-04)

V. Petrov; CLEO Technical conference (San Francisco, CA, USA, 2018-05)

V. Petrov; Conference on Lasers and Electro-Optics CLEO/Pacific Rim, (Hong Kong, China, 2018-07)

46 2.1: Time-resolved XUV-science

A. Rouzée, S. Patchkovskii (project coordinators) and F. Branchi, F. Brauße, T. Bredtmann, L. Drescher, U. Eichmann, T. Fennel, F. Furch, A. Harvey, L. Hecht, E. Ikonnikov, M. Ivanov, A. Jiménez Galàn, A. Husakov, K. Kolatzki, O. Kornilov, M. Kretschmar, B. Langbehn, N. Mayer, J. Mikosch, N. Monserud, F. Morales Moreno, T. Nagy, M. Osolodkov, S. Raabe, G. Reitsma, M. Richter, H.-H. Ritze, H. Rottke, D. Rupp, M. Sauppe, F. Schell, C. P. Schulz, B. Schütte, B. Senfftleben, O. Smirnova, V. Shokeen, M. T. Talluri, R. M. Tanyag, M. J. J. Vrakking, T. Witting, S. Yarlagadda, J. Zimmermann

1. Overview versidad Complutense de Madrid, Spain); H. Köppel, A. Kuleff (Universität Heidelberg); T. Müller (TU Berlin), The main goal of project 2.1 is to visualize, understand, K.H. Meiwes-Broer, I. Barke (Universität Rostock); B. v. and control electron and atomic motion during trans- Issendorff (Universität Freiburg); P. Piseri (Università di formation of finite quantum systems, starting from few- Milano, Italy); M. Kling (LMU Munich); P. Hommelhoff body systems to isolated nanoparticles. The project has (FAU Erlangen); T. Brabec (University of Ottawa, Can- both experimental and theoretical components. Exper- ada); G.G. Paulus (Universität Jena); C. Menoni (Colo- imentally, we are developing a framework of closely rado State University, USA), A. Orr-Ewing, M. Ashfold interconnected time-resolved methods, unified by the (University of Bristol, UK). application of novel XUV/X-ray light sources, both table-top, such as obtained by high harmonic generation In-house collaborations with projects 1.1, 1.2, 2.2, 3.1 (HHG), as well as at free electron laser facilities. Using and 4.1. photoionization as a probe step in a pump-probe con- figuration, we investigate attosecond electron motion in atoms, molecules and nanoparticles and its coupling with the nuclear motion. This is done by combining the 3. Results in 2018 extreme temporal resolution (attosecond) with atomic-scale spatial resolution provided by these new light T1: Attosecond electronic dynamics in strongly sources. Our experimental framework is complemented driven systems by an advanced theory program aiming at (i) tracking down and resolving correlated multi-electron dynamics Attosecond transient absorption spectroscopy on the attosecond time scale, and (ii) understanding the impact of coherently excited attosecond multi-electron The investigation of field-driven motion of electrons in dynamics on the longer, femtosecond-scale nuclear mo- atoms, molecules and solids is of widespread current tion. Our common goal is to push atomic and molecular research interest and has led to numerous innovations science beyond the present state-of-the-art by looking at in the last decades, ranging from techniques for the ma- the new time scale in chemical and physical processes nipulation of molecules, such as molecular alignment or optical tweezers, to strong-field ionization and recombination phenomena such as high harmonic generation or electron recollision. The generation of isolated attosec- 2. Topics and collaborations ond pulses from high harmonic generation has opened the possibility to study these field-driven responses ex- Presently, the project is organized in four topics: perimentally on their natural timescale.

T1: Attosecond electronic dynamics in strongly Attosecond transient absorption spectroscopy (ATAS) is driven systems one of these experimental techniques and has been used to study the sub-cycle dipole responses in rare gas atoms T2: Strongly-coupled electronic and nuclear dynam- and diatomic molecules. In ATAS, atoms, molecules or ics in photoexcited neutral molecules solids are subject to a moderately intense NIR field and an XUV attosecond pulse train or isolated pulse, whose T3: Ultrafast electronic decay and fragmentation dy- relative phase is controlled. The spectrally broad XUV namics at XUV and x-ray wavelengths pulse excites electrons in the materials and the effect of the NIR field is inferred from the observed modifica- T4: Collective and correlated electron dynamics at tion of the free induction decay of the excited electrons. the nanoscale In a very recently published work from project 2.1, ATAS has been extended to polyatomic molecules for Collaborations with: A. Rudenko, D. Rolles (Kan- the first time [DRW19]. In this study, the state-resolved sas State University, USA); J. Küpper (Center For induced-dipole response of iodomethane (CH3I) mole- Free-Electron Laser, Hamburg); H. Stapelfeldt (Aarhus cules was studied by the ATAS of the iodine 4d core-to- University, Denmark); K. Ueda (Tohoku University, Ja- valence and core-to-Rydberg transitions. It was shown, pan); F. Calegari (CFEL, Hamburg); F. Lépine (Institut that the strength of the induced dipole response of the Lumière et Matière, France); D. Holland (Science and core-to-Rydberg transitions is much stronger than that Technology Facility Council, UK); Th. Pfeiffer (Max of the core-to-valence transition. This observation re- Planck Institute for Nuclear Physics, Germany); K. Var- sults from the higher polarizability of the Rydberg states. ju (University of Szeged, Hungary); L. Bañares (Uni- Our work demonstrated that ATAS is suitable to study

47 the polarizability of electronic states from a local perspective of the reporter in the molecule on a sub-cycle timescale. Furthermore, it could be shown that a principle component analysis (by means of a singular val- 100 ue decomposition) is a powerful tool to robustly extract 5 and separate the temporal and spectral components of 80 the AC Stark effect on the excited states, isolating them 0 60

from pathway interference signals and statistical noise 3 40 in the measurement (see Fig. 1). -5

20 x 10 A Δ -10 Time Delay [fs ] Time 0 (c) 0.50 -15 -20

0.25 -10 50 55 60 0.00 Photon energy [eV]

] -0.25 ω

U [ Fig. 2: -0.50 Transient change of absorbance of CH3I in the 4d-to- -0.75 valence and 4d-to-Rydberg spectral region. Shown is a 28 fs range of XUV-NIR time-delays near time overlap. -1.00 At positive time-delays the NIR pulse arrives at the 48 50 52 54 56 58 60 62 sample before the XUV pulse. A strong transient absor- Energy [eV] bance is associated with the 4d-to-Rydberg transitions, while the response of the 4d-to-valence transitions Fig. 1: remains weak. Slanted bands of oscillating transient (a) Singular values resulting from singular value decom- absorbance are associated with two-pathway-interfe- position of experimental (blue) and calculated (orange) rences for populating core-excited Rydberg states. The transient change of absorbance. The leading singular two weaker replicas of the observed features at nega- value associated to the light-induced phase signal is tive time-delays can be associated with independently much stronger than trailing singular values correspond- characterized pre-pulses of the NIR laser. ing to hyperbolic features and statistical noise. (b),(c) Singular vectors associated with the dominant singular value. Displayed in (b) is the temporal component V(τ) of periodicity of the driving NIR fi eld (hence called 2ω oscil- the experimental data (blue), of the calculated data with lations). These originate from interferences of pathways a Gaussian envelope (orange) NIR-fi eld or a NIR-fi eld that are coupled by two NIR photons. While observation of reconstructed from a SEA-F-SPIDER characterization features oscillating at higher even multiples of the NIR fi eld (green). The spectral component U(ω) displayed in (c) has been reported, odd numbered multiples were thus far exhibits the different response of the core-to-valence (σ*) never observed in ATAS. This is rationalized by the parity and core-to-Rydberg transitions (6p) originating from the violation that would occur from coupling pathways that are state-specifi c polarizability. separated by an odd number of NIR photons.

In unpublished work, we have shown numerically that for Fig. 2 shows the measured ATA spectrum of the CH3I io- systems which lack inversion symmetry, such as hetero- dine 4d-1 spectral region [DRW]. In addition to the light nuclear molecules, oscillating features at the frequency induced phase features - prominent around the Rydberg of the NIR fi eld should be observable in ATAS measure- resonances (6p) and weaker around the valence res- ments. Since parity is not conserved in non-centrosym- onances (σ*), which are caused by a transient shift of metric systems, interference of excitation pathways can the excited state energy due to the AC Stark effect, the be driven by one NIR photon. Theory predicts that these transient spectrum shows hyperbolic perturbed induction new features are dependent on the direct electric fi eld decay lines at delays where the NIR pulse arrives long (in contrast to the electric fi eld intensity in the atomic after the XUV pulse. Features oscillating with a period of ATAS) and as such would allow to extract additional approximately 1.3 fs (2ω) can be observed in the region phase-information from the spectroscopy data that is of the time overlap close to 0 fs delay, originating from absent in the parity-conserving case. In order to ob- pathway interferences from fi eld-free excited states and serve the described effect experimentally, ATAS has to laser dressed states: Due to the coupling of the excited be combined with the manipulation of spatial molecular Rydberg 6p states to Rydberg states of 6s character, orientation. We are working towards this goal. the molecules can absorb or emit two NIR photons and a corresponding XUV photon of lower or higher energy Towards attosecond coincidence imaging experiments to reach the Rydberg 6p state, leading to an interference at high repetition rate with the direct excitation pathway (see [DRW] for details). Early in 2018 the 100 kHz high repetition rate XUV-IR To date, ATAS studies have mostly focused on features pump-probe setup has been assembled in its fi nal form. that are oscillating in XUV-NIR time-delay with half the A velocity map imaging (VMI) spectrometer has been

48 integrated into the setup to implement the Reconstruc- µJ) were focused in a 2 mm long cell fi lled with 90 mbar tion of Attosecond harmonic Beating By Interference of of krypton to generate XUV radiation. By measuring Two-photon Transitions (RABBITT) and the attosecond the current from a XUV photodiode the photon fl ux of streaking methods for characterizing the overall system the XUV radiation was estimated to be ~106 photons properties such as pulse duration and pump-probe sig- per pulse. The XUV pulse and the IR probe pulse were nal stability. The main goal in 2018 was to demonstrate focused into the VMI to ionize neon atoms from a jet the production of isolated attosecond pulses (IAP) at target. The resulting attosecond streaking spectrogram 100 kHz repetition rate for future experiments, which that was recorded is shown in Fig. 5. One clearly rec- will employ a reaction microscope for electron-ion co- ognizes the streaking modulation that characterizes an incidence studies in small to medium-sized molecules. isolated attosecond pulse. Also, the observed fringes in the spectrogram indicate the presence of a small satel- To reach this goal, the 100 kHz 800 nm OPCPA, which lite pulse. Preliminary results from pulse retrieval using delivers 7 fs (FWHM) pulses with up to 190 µJ pulse a time-domain ptychography algorithm confi rm the pres- energy, has been extended by a neon fi lled hollow-core ence of a single attosecond XUV pulse accompanied fi bre. After nonlinear pulse compression sub-4 fs pulses by small satellites. To reduce the satellite pulse we can (1.5 cycles) have been observed with pulse energies up employ additional gating schemes, e.g. polarization gat- to 90 µJ. For the generation of IAPs not only ultra-short ing or double optical gating, or use an XUV fi lter foil with pulses are essential but also the carrier-envelop-phase a higher energy transmission window. In summary, the (CEP) stability plays a crucial role. In a joint effort with the 100 kHz attosecond beamline has been fully commis- group of Gerhard Paulus (University Jena) the CEP of sioned and we demonstrated the possibility to generate the 3.6 fs pulses has been measured on a single-and-ev- and use isolated attosecond pulses. In the near future ery shot basis at full 100 kHz repetition rate [HFW18]. the reaction microscope will be integrated into the setup For more details on the 100 kHz 800 nm OPCPA replacing the presently used VMI. This will enable ex- system see project 4.1. periments to study correlated electron-ion dynamics in small molecules on the attosecond time scale.

40 ] 35 1 4 30 2 25 0.5 0 20 Energy + Ip [eV 15 -2 -20 -10 0 10 20 τ [fs] 0 -4 -5 0 5 -20 0 20 Time [fs] Time [fs] Fig. 3: RABBITT trace from XUV pump pulses generated by 7 fs pulses focused into an argon fi lled cell and weak Fig. 4: IR probe pulses. Retrieved attosecond pulse train (right) and IR fi eld (left). The middle pulse of APT has a width of 220 as (FWHM) and the main IR pulse has a pulse duration of 7.7 fs As a fi rst test, 7 fs IR pulses with approximately 120 µJ (FWHM). were focused by a spherical mirror into a 2 mm long cell fi lled with 90 mbar of Argon. The resulting XUV Attosec- ond Pulse Train (APT) was overlapped with an IR probe T2: Strongly coupled electronic and nuclear dynam- pulse and both were focused into an Argon jet inside the ics in photoexcited neutral molecules VMI in order to record a RABBITT trace (see Fig. 3). At long delay one clearly sees photoelectron spectra from Conical intersections are omnipresent in photoexcited argon generated by the 13th to 23rd harmonics. Around molecules and play a key role in determining the out- zero delay sidebands appear caused by two photon come of a photochemical reaction process. Our ability interferences. The shape of the APT and the IR probe to visualize in real-time charge redistribution as a mole- pulse were retrieved from the RABBITT measurement cule evolves from reactant to product is relevant in ma- using a retrieval algorithm based on time-domain-pty- ny chemical processes. Novel approaches based on ta- chography and are shown in Fig. 4. The XUV pulse con- ble-top high harmonic generation (HHG) are now being sists of a train of 5 pulses with a strong central pulse, developed to investigate ultrafast molecular dynamics. with a full width at half maximum of 220 as. The IR pulse X-ray transitions are element-specifi c and chemically (right panel) has a pulse width of 7.7 fs (FWHM) with a selective. In this spectral region, absorption occurs lo- smaller pre-pulse due to residual negative third order cally at the atomic cores and X-ray measurements at dispersion. atom-specifi c absorption edges enable the investigation of both the electronic structure and the chemical coordi- In a second experiment we have post-compressed the nation environment of the absorbing element, providing 7 fs output pulses from our OPCPA system to <4 fs in a local probe of the dynamics under study. For exam- a hollow core fi bre setup. These pulses (with up to 90 ple, the transient electronic structure during ultrafast

49 60 60

50 50

40 40

30 30 Energy + Ip [eV] Energy + Ip [eV]

20 20 -10 -5 0 5 10 15 -10 -5 0 5 10 15 τ [fs] τ [fs]

2 0.8

2 0

[t]|

2 0.6 )| xuv )) [rad] ω ω ( -2 0.4 ( xuv xuv of |E |E 10 -4 0.2 log arg(E

-6 0 -6 -4 -2 0 2 4 6 20 30 40 50 60 Time [fs] Photon energy [eV]

Fig. 5: (a) shows photoelectron spectra from neon target ionised by the XUV pulse in the presence of a strong IR field as a function of XUV-IR-delay (streaking trace). A time-domain-ptychography algorithm has been used to reconstruct the IR and XUV pulses. The retrieved trace is shown in (b). The reconstructed electric field of the strong IR pulse is shown as red line in (c). The blue line in (c) is a plot of the intensity envelope of the XUV pulse on logarithmic scale. (d) shows the XUV spectrum (solid line) and spectral phase (dashed line).

bond-cleavage and ring opening of gas-phase molecules has been successfully investigated by time-re- 80 solved x-ray absorption spectroscopy at the C K-edge using an HHG source [PSM17, ABP17]. However, the 60 limited conversion efficiency of the HHG process at high 40 photon energy has restricted the potential of table-top 20 soft x-ray sources for time-resolved x-ray absorption experiments. 100

In collaboration with project 3.1, we have recently developed a table-top soft x-ray source based on HHG -1 to enable femtosecond soft x-ray absorption spectros- 10 copy experiments in the water-window spectral range (280-540 eV). A high-energy commercial Ti:Sa laser system delivering 30 mJ pulses at a repetition rate of Normalized intensity 10-2 1 kHz was used to generate tunable mid-infrared pulses 300 350 400 450 with 3 mJ of pulse energy using an optical parametric Photon energy [eV] amplifier. HHG was performed in a 5 mm long gas cell maintained at a constant high gas pressure of helium Fig. 6: (~4 bars) using 1.8 mm pulses. The spectrum of the soft a) CCD image of high harmonics recorded with the x-rays was recorded using a home-made flat field spec- soft x-ray spectrometer and corresponding spectrum trometer composed of an aberration-corrected, concave b) obtained by vertical integration of the image and gratings with a variable line spacing (VLS) and a du- calibration of the detector. al-microchannel plate + phosphor screen assembly. We measured an HHG spectrum extending from 270 eV to 440 eV, with an estimated minimum total flux at the T3: Ultrafast electronic decay and fragmentation dy- source of (7.4±1.0) x 106 photons/s and a pulse energy namics at XUV and x-ray wavelengths of 0.35±0.05 pJ [KEG] (see Fig. 6). Clear harmonic lines spaced by twice the laser frequency (1.38 eV) were also Molecular dynamics studied by time-resolved spectros- observed below 300 eV (see inset of Fig. 6). The source copy employing XUV photons often involves investi- will be used in a near future to probe charge transfer gation of excited molecular cations prepared at these processes involving coupled electronic and nuclear short wavelengths. The XUV time-delay-compensating motion in a number of molecular systems, including in monochromator beamline that has been developed push-pull chromophores. at MBI few years ago is most suitable for these stud-

50 ies providing not only femtosecond time-resolution, fi ned scenario to investigate correlated dynamics of but also wavelength-selected XUV pulses allowing for highly excited matter. Employing diffractive imaging of separation of relaxation processes initiated at different single nanoparticles in free fl ight with short-wavelength XUV wavelengths. Following the study of dissociative free-electron lasers (FELs) and HHG sources, we can ionization and autoionization of nitrogen, the relaxation study the light-induced dynamics with high spatial and + processes in CH3I cations were studied in the vicinity temporal resolution. From the measured diffraction pat- of the dissociative ionization threshold (the study is in terns, formed by the interference of elastically scattered collaboration with the group of Prof. Luis Bañares, Com- photons, the nanoparticle’s structure can be determined. plutense University of Madrid). At a photon energy of This allows resolving the structure of non-depositable 10.9 eV, competition between autoionization and neutral specimen, such as superfl uid helium nanodroplets, and dissociation was observed. At higher photon energies visualizing femtosecond/picosecond structural changes of 14.0 eV and 17.2 eV, vibrationally and electronically like laser-induced melting. Even faster electron dynam- excited cations were prepared and the dissociation was ics can be mapped by diffractive imaging as such dy- induced using the probe IR pulse. namics are also changing the scattering response.

The three-dimensional shapes of spinning helium nanodroplet

In 2018, the results of an experiment, carried out in collaboration with the group of Thomas Möller (TU Berlin), together with the team of Carlo Callegari at the LDM

Yield (low-density matter) instrument of the FERMI Free-Elec- tron Laser in Trieste, were published in Physical Review Letters [LSO18]. Using intense XUV pulses from FER- MI, we measured wide-angle diffraction images of superfl uid helium nanodroplets to map out the droplets’ shapes in great detail (see Fig. 8).

The equilibrium shape of a classical liquid drop is determined by the competition of surface tension and centrifugal force. With increasing angular momentum, the shape evolves from spherical to oblate and prolate up to a dumbbell-like structure before fi ssioning into two sep- Yield arate drops. In contrast, a superfl uid droplet with zero viscosity cannot rotate as a rigid body. Instead, quan- tized vortices are formed inside the droplet that store the rotational energy. This effect is expected to infl uence the equilibrium shapes of the droplet. Delay [fs]

Fig. 7: Oscillations of fragment cation yields following dis- + sociation of CH3I cations prepared by femtosecond XUV pulses at 14.0 eV.

The results depicted in Fig. 7 showed that dissociation proceeds along different pathways involving localization of the charge on one or the other fragment (either CH3+ or I+) depending on the location of the vibration wavepacket at the moment of the arrival of the probe pulse. Fig. 8: Preliminary theoretical analysis showed, that the local- Evolution of helium nanodroplet shapes. Recorded scat- ization process requires consideration of both the main tering images (upper row), simple model shapes (middle dissociative vibrational coordinate (CH3-I) as well as the row), and corresponding calculated diffraction patterns accompanying umbrella mode of the CH3 fragment. Full (lower row) [LSO18]. theoretical calculations are under way in collaboration with Jesus González-Vázquez. In our three-dimensional analysis of the wide-angle diffraction patterns, we could retrieve the droplets’ di- T4:Collective and correlated electron dynamics at mensions and found a surprisingly close resemblance the nanoscale of the superfl uid droplets to their classical counterparts (see Fig. 9). Classically unstable shapes as reported in Excitation of nanoparticles, such as clusters and nano- a landmark paper on the pioneering experiment at LCLS droplets, with intense laser pulses provides a well-de- were not observed [GFC14]. In particular, the large sta-

51 tistics obtained in our experiment in combination with the benefit of wide-angle diffraction imaging to include Orginal spectrum on phosphor screen [MCP] three-dimensional information allowed us to exclude the 17.5 presence of extremely oblate particles reported previ- 20.5 ously. At the same time, the huge data sets of diffraction Hight [nm] 10 15 20 25 30 imaging experiments impede manual classification. This Width [nm] led us to the development of a new classification ap- HHG spectrum after filter (normalized) proach based on a neural network for automated pattern 1.0 recognition [Zim19]. 0.8

0.6

0.5 0.2 oblate analyt. model branch num. model 0.0 0.4 data this work 11 13 15 17 19 Harmonic order

0.3 /V 3 Fig. 11: b 0.2 HHG spectrum obtained in Xe. In the upper image the spectral component is shown across the horizontal axis, prolate 0.1 branch and the vertical axis shows the HH beam divergence in vertical direction. The lower image shows the calibrated 0.0 spectrum integrated across the vertical direction. 1.0 1.5 2.0 2.5 3.0 3.5 Aspect ration a/c aging has been the realm of free-electron laser science until recently. As reported last year, the development of extremely intense HHG sources in the XUV regime (1012 W/cm² on target) together with a favorable combi- Fig. 9: nation of wavelength and target material allowed us to Comparison of the fitted geometries with calculations obtain bright single-droplet diffraction images of helium for classical droplets (principal semiaxis lengths a, b, c, nanodroplets at the MBI [RML17]. In 2018 we extended droplet volume V). [LSO18] the setup with an infrared pump – XUV probe capability and obtained first time-resolved diffraction data to resolve laser-induced excitation and ionization dynamics in xenon-doped helium nanodroplets.

x 108 Average intensity 250 brightest hits 6.5 For intense IR pulses in the range of 1015 W/cm², we could trace the IR-induced destruction of the droplets 6 on a picosecond timescale, but extremely intense fluo-

5.5 rescence buried the diffraction patterns at shorter times where the interesting electron dynamics would be ex- 4..5 pected. Attenuating the IR intensity to a few 1012 W/cm² allowed us to observe diffraction patterns for all pump- 4. probe delays, with only small amounts of fluorescent Intensity [arb. u.] 3.5 light superimposed. In this regime, we detected a pronounced decrease of the diffracted intensities as well 3 as a change of the structures in the diffraction images, 150 -100 -50 0 50 100 150 Delay [fs] when the IR and XUV pulses were overlapping. The averaged intensity of the 250 brightest images of each time delay is given in Fig. 10, indicating a decreased Fig. 10: image brightness in a 100-femtosecond-window around In a small time window around time zero, the brightness time zero. The temporal resolution of the experiment of the diffraction images is decreased due to an ultra- was limited by the pulse durations (on the order of 35 fast bleaching process that has to be further analyzed fs). The data analysis is ongoing, in close connection and studied. to theoretical efforts to develop a physical picture that explains the observed ultrafast bleaching process.

HHG-based time-resolved diffraction imaging of ultra- A higher time resolution will be achievable with the new fast bleaching in helium nanodroplets beamline for intense attosecond experiments, currently under development in the XPL (Extreme Photonics Lab, To observe and follow ultrafast electron dynamics in former High-Field Lab) at MBI. In 2018, the terawatt OP- photoexcited nanoparticles via diffractive imaging, we CPA system developed in this laboratory became fully can employ pump-probe schemes benefiting from good operational. The system produces 3-cycle pulses (8 fs temporal and spectral control of high-harmonic gener- FWHM) with 30 mJ pulse energy at a repetition rate ation sources. Single-shot single-particle diffraction im- of 100 Hz. The CEP stability of the system has been

52 demonstrated as well. For a more detailed description Other Publications see project 4.1. PSM17: Y. Pertot et al.; Science 355 (2017) 264 In December 2018 first HHG pulses have been generated using the terawatt OPCPA system (see Fig. 11). An ABP17: A. Attar et al.; Science 356 (2017) 54 experimental endstation consisting of a velocity-map imaging spectrometer, a split-and-delay unit, as well as an GFC14: Gomez et al.; Science 345 (2014) 906 XUV focusing mirror is currently under construction. It is planned to use this endstation for first experiments in KSL12: Kassemeyer et al.; Opt. Express 20 (2012) 4149 atoms and clusters with intense attosecond pulse trains within 2019 and for time-resolved diffraction imaging BTK15 Bobkov et al.; J. Synchrotron Rad. 22 (2015) studies. 1345

Zim19: J. Zimmermann et al.; in preparation for Phys. Rev. E (2019)

Own Publications in 2018 ff RML17: D. Rupp et al.; Nat. Comm. 8 (2017) 493 (for full titles and list of authors see appendix 1)

ABA18: F. Allum et al.; J. Chem. Phys. 149 (2018) 204313 Invited Talks at International Conferences (for full titles see appendix 2) ASB18: K. Amini et al.; Struc. Dyn. 5 (2018) 014301/1-13 L. Drescher; Gordon Research Conference, Photoioniza- BGA18: F. Brauße et al.; Phys. Rev. A 97 (2018) tion and Photodetachment (Galveston, TX, USA, 2018 -02) 043429/1-10 T. Fennel; QUTIF annual meeting 2018 (Hamburg, Ger- DKW18: L. Drescher et al.; Nature 564 (2018) 91 many, 2018-02)

EMB18: B. Erk et al.; J. Synchrot. Radiat. 25 (2018) T. Fennel; Theory Seminar, AG Berakdar (University 1529-1540 Halle, Germany, 2018-06)

HFW18: D. Hoff et al.; Opt. Lett. 43 (2018) 3850-3853 T. Fennel; EUCALL workshop: Theory and simulation of photon-matter interaction (Szeged, Hungary, 2018-07) KAB18: M. Kübel et al.; J. Phys. B 51 (2018) 134007/1-8 T. Fennel; 19th International symposium on small parti- KPG18: D. Koulentianos et al.; Phys. Chem. Chem. cles and inorganic clusters (Hangzhou, China, 2018-08) Phys. 20 (2018) 2724-2730 T. Fennel; International workshop attosecond physics at LSO18: B. Langbehn et al.; Phys. Rev. Lett. 121 (2018) the nanoscale (Daejon, South Korea, 2018-10) 255301 A. Rouzée; 9th Int. Meeting on Atomic and Molecular LST18: Q. Liu et al.; J. Opt. 20 (2018) 024002/1-13 Physics and Chemistry (Berlin, Germany, 2018-06)

MBK18: B. Major et al.; JOSA B 35 (2018) A32-A38 D. Rupp together with N. Monserud, M. Sauppe, J. Zim- mermann, K. Kolatzki, B. Schütte, M. J. J. Vrakking, T. MWW18: P. Matía-Hernando et al.; J. Mod. Opt. 65 Fennel, and A. Rouzée; DESY User Meeting (Hamburg, (2018) 737-744 Germany, 2018-01)

NKS18: C. Neidel et al.; Chem. Phys. 514 (2018) 106-112 D. Rupp together with K. Kolatzki, M. Sauppe, B. Senfftleben, J. Zimmermann, and T. Fennel; Science at SPH18: L. Seiffert et al.; J. Phys. B 51 (2018) 134001/1-7 FELs 2018 (Stockholm, Sweden, 2018-06)

SRE18: M. Sauppe et al.; J. Sync. Rad. 25 (2018) 1-12 M. Sauppe; SNI 2018 German Conference for Research with Synchrotron Radiation, Neutrons and Ion Beams at YUG18: L. Young et al.; J. Phys. B 51 (2018) 032003/1-45 Large Facilities (Munich, Germany, 2018-09)

B. Schütte; DPG Frühjahrstagung (Erlangen, Germany, 2018-03) in press B. Schütte; 27th Annual Int. Laser Physics Workshop DRW: L. Drescher et al.; J. Chem. Phys. Lett. (Nottingham, UK, 2018-07)

KEG: C. Klein et al.; J. Phys. Chem. Lett. B. Schütte; Workshop on Atomic Physics (Dresden, Ger- many, 2018-11)

53 2.2: Strong-field Few-body Physics

F. Morales Moreno, H. Rottke (project coordinators) and D. Ayuso , W. Becker, U. Bengs, F. Branchi, T. Bredtmann, U. Eichmann, M. Ivanov, Á. Jiménez, T. Kalousdian, J. Kaushal, S. Meise, L. Merkel, J. Mikosch, D. B. Milosevic, S. Patchkovskii, H. R. Reiss, M. Richter, A. Rouzée, F. Schell, C. P. Schulz, B. Schütte, O. Smirnova, P. Stammer, M. T. Talluri, S. Yarlagadda, N. Zhavoronkov

1. Overview (FOM-Institute for Plasma Physics, Rijnhuizen, The Netherlands), A. Stolow, A. E. Boguslavskiy (Steacie On a sub-femtosecond temporal and Ångström spatial Institute for Molecular Sciences, National Research scale the project aims at Council of Canada, Ottawa, Canada), F. Martín (Uni- versidad Autónoma de Madrid, Madrid, Spain), H. Sta- • understanding the strong field induced dynamics in pelfeldt (Aarhus Univ., Aarhus, Denmark), J. Küpper, A. atoms and molecules, Rubio (Center for Free Electron Laser, Univ. Hamburg), • employing strong field processes as a tool for imag- T. Fennel (Univ. Rostock), A. I. Kuleff (Univ. Heidel- ing and understanding atomic and molecular elec- berg), M. Krikunova (TU Berlin), V. R. Bhardwaj (Univ. tron dynamics and molecular structural changes, of Ottawa, Canada), R. Cireasa (Institut des Sciences • using tailored light pulses to manipulate electronic Moléculaires d’Orsay, France), F. Legare (ALLS Mon- motion, generate high-order harmonics with specif- treal, Canada), H. Köppel, A. Kuleff (Univ. Heidelberg), ic polarization characteristics and investigate chiral V. S. Makhija, (Univ. of Ottawa, Canada), J. P. Wolf phenomena. (Univ. Geneva, Switzerland), M. Kleber (TU München)

We put specific focus on the fundamental aspects of In-house collaborations with Projects 1.1, 2.1 and 4.1. strong field induced multi-electron dynamics, on the excitation of neutrals, on the forces exerted on these neutrals, on the role played by molecular structure and dynamics and on manipulating electronic dynamics. 3. Results in 2018 The strong field regime of interaction of light with matter is typically entered at light intensities beyond 1013 Watt/ T1: Single- and multi-electron strong field phenome- cm2 in the infrared spectral range. There, the electric na and their resolution in time field of the light wave starts to become comparable with the intra-atomic/intra-molecular field experienced by Strong-field excitation of molecules and the observation the valence electrons. of channel closings

Recent experiments on strong-field excitation in the tunneling and in the multiphoton regimes demonstrated the 2. Topics and collaborations role played by channel closings. A thorough analysis of the experimental results led to a reconciliation of the mul- We address our objectives via experiment and closely tiphoton and tunneling pictures [ZPI17]. We now have linked theory focusing on these topics: extended our investigations towards the study of strong- field excitation of molecules. The subject is still an open T1: Single- and multi-electron strong field phenome- field in strong-field physics and is considered one of the na and their resolution in time future perspectives for studies in simple molecules such as H2 [ILB18], which has been extensively studied oth- T2: Dynamics of strong field ionization of ordered erwise. structures and clusters While neutral excited fragments in the strong-field disso- T3: Probing molecular dynamics by strong field ion- ciation and Coulomb explosion of molecules have been ization studied within the framework of frustrated tunneling ionization (FTI) [MNG09], there are only a few theoretical T4: Quantum dynamics in tailored fields studies and only singular experimental work on strong- field excitation of neutral molecules. Collaboration partners: G. G. Paulus (Friedrich Schiller Univ., Jena), C. Faria (City College London, London, We report on the successful observation of strong-field UK), S. P. Goreslavski, S. V. Popruzhenko (National Re- excitation of H2 and N2. Moreover, we found channel search Nuclear University (MEPhi), Moscow, Russia), closing effects in the intensity dependent yield of the A. Saenz (HU Berlin), Y. Mairesse (CELIA, Université excited molecules. The measured yields of excited H2* Bordeaux, Bordeaux, France), N. Dudovich (Weizmann and N2* were contrasted with the strong-field excitation Institute, Rehovot, Israel), J. Marangos (Imperial Col- yield for Ar*, for which channel closings have been ob- lege, London, UK), X. J. Liu (Chinese Academy of Sci- served recently [ZPI17]. Due to similar binding energies ences, Wuhan, China), J. Chen (Beijing Univ., Beijing, of Ar, H2, and N2, 15.76 eV, 15.43 eV, and 15.58 eV, re- China), T. Marchenko (Université Pierre et Marie Curie, spectively, a comparison might help to extract differenc- Paris, France), J. M. Bakker, G. Berden, B. Redlich es between channel closings in atoms and molecules.

54 Reasons for differences could have their origins in the To identify the metastable states the excited molecules polarizability of the molecules and in contributions from decay to before reaching the detector, our experiments occupied molecular orbitals below the highest occupied were designed to measure roughly the decay time of the molecular orbital (HOMO). Furthermore, the polarization metastable states and to obtain information on the spin axis of the laser with respect to the molecular axis might state of the molecule by performing a Stern-Gerlach play an important role. Our current experimental capa- type experiment (using an inhomogeneous magnetic bilities do not allow for aligning the molecules. Thus the field which is not shown in the sketch of the experiment 3 experiment provides averaged yields. in Fig. 1). As a result, we identify the c Πu state as the metastable state in H2 with a lifetime >1 ms. For N2 we 1 Our experimental setup has been basically described assign the a Πg state to the metastable state, with a elsewhere [ZiE16, ZPI17]. Standard Ti:Sapphire laser measured lifetime ≤170 μs. At this point, it is not clear pulses at 800 nm with a pulse duration of 50 fs (FWHM) exactly how these long lived states are populated. and 1 kHz repetition rate, are frequency doubled in a 0.3 mm thick BBO crystal. The linearly polarized fre- In Fig. 2 we present our results of the intensity depen- quency doubled laser beam is focused into a superson- dent strong-field excitation yield for H2* and N2*. For ic molecular beam (this replaces the effusive beam de- comparison we also show the yield of excited Ar* at- scribed in [ZiE16, ZPI17]) with a beam waist of ~12 μm, oms, which serves as a reference due to its well estab- where it interacts with the target molecules (atoms). In lished channel closing at 6 photons [ZPI17]. Surprising- order to detect excited states of molecules we rely on a ly, we observe for both molecules a strong increase in direct method [NGS08, ENR09] rather than on field ion- the yields as in the atomic case, indicating that channel ization. We thus measure the surviving population in an closings seem to be also observable in molecules. In excited state that lives long enough to reach the detec- the H2 curve one clearly recognizes a pronounced step tor excited. In rare gas atoms this is most likely a meta- which is, however, significantly less high than in the Ar* stable state populated via fluorescence decay of the ini- case. N2* also displays a strong increase in the vicinity tially populated state. Thereby, the surviving population of the 6 photon channel closing but is found to increase in the metastable state impinging on the multi-channel over a larger intensity range. These encouraging results plate detector and initiating the detection process is to await a thorough theoretical analysis by the group of A. a good approximation proportional to the initial excited Saenz to unravel the influence of molecular orbitals on population. The excitation energy of the lowest excited channel closings. (metastable) states is typically sufficient to detect neutral excited atoms (molecules). At the beginning of the ex- . perimental work there was the question whether a long 1000 lived metastable state in molecules could be reached by strong-field excitation. One finds the answer displayed in 100 Fig. 1, where we show a typical time of flight spectrum of neutral excited H2 molecules and neutral excited frag- 10 ments. At short flight times less than 50 μs we observe the known spectra of excited neutral fragments from the 1 Coulomb explosion (CE) and from the dissociation due to

bond softening [MNG09]. At later times around 150 μs a [arb. units] Yield 0.1 relatively strong signal identified by its flight times as excited H2* molecules becomes prominent. Similar spectra 0.01 have been obtained for N2*, but with much longer time of 10 100 1000 flight for the molecule due to the heavier mass. Intensity [TW/cm2]

Fig. 2:

Measured excitation yields for H2 and N2 around the 1600 6 photon channel using a frequency doubled Ti:Sa la- 400 ser at 400 nm. The laser intensity has been normalized 140 to the Ar* data. 120 100 80 T2: Dynamics of strong field ionization of ordered 60 structures and clusters

Yield [arb. units] Yield 40 20 Low-energy structure following strong-field ionization of 0 60 120 180 240 300 clusters Time of flight [µs] For the past 30 years intense laser-cluster interactions have been seen primarily as a way to generate ener- Fig. 1: getic ions and electrons. In surprising contrast with the

Detection of strong field excited states of H2* via their hitherto prevailing paradigm, it was recently found that decay into a long lived metastable state. copious amounts of relatively slow electrons are also produced in intense laser-cluster interactions. These

55 low-energy electrons constitute a previously missing link We found the emission of slow electrons to be a very in the understanding of the processes occurring when efficient process, enabling a large number of slow elec- an intense laser pulse interacts with a nanoscale parti- trons to escape from the cluster. As a consequence, it cle, a situation that is highly relevant for the in-situ imag- becomes much harder for highly charged ions to find ing of biomolecules on ultrashort timescales. partner electrons that they can recombine with, and many of them indeed remain in high charge states. The When a nanoscale particle is exposed to an intense la- discovery of the so-called low-energy electron struc- ser pulse, it transforms into a nanoplasma that expands ture can thus help to explain the observation of high- extremely fast. Several phenomena occur that are both ly charged ions from intense laser-cluster interactions fascinating and important for applications. Examples are that was discovered already more than two decades the generation of energetic electrons, ions and neutral at- ago. Our findings might be important as low-energy oms, the efficient production of X-ray radiation as well as electrons are implicated as playing a major role in radi- nuclear fusion. While these observations are rather well ation damage of biomolecules – of which the clusters understood, another observation, namely the generation are a model. of highly charged ions, has so far posed a riddle to researchers. The reason is that models predicted very efficient recombination of electrons and ions in the nanoplasma, thereby drastically reducing the charges of the ions.

In collaboration with the Imperial College London, we recently showed that the vast majority of electrons from strong-field ionized clusters are very slow [SPA18]. Moreover, it turned out that these low-energy electrons were emitted with a delay compared to the energetic electrons. The observations were independent from the specific cluster and laser parameters used, and they help to understand the complex processes evolving on the nanoscale.

300 Fig. 4: Atomistic simulation of the laser-induced cluster explosion

200 Evolution of a molecular shape resonance during bond -stretching 100

Signal [arb. units] Molecular shape resonances are very well-known pro- Kinetic energy [eV] cesses describing the trapping of an electron in a qua- 0 si-bound state that results from the interplay between 1 2 3 4 5 Kinetic energy [eV] the coulombic and centrifugal potential. Such resonances are often observed in electron impact experiments on atoms and small molecules and in single-photon ioniza- Fig. 3: tion experiments, where they appear as broad continu- The electron kinetic energy spectrum from argon clus- um resonances few eV above an ionization edge in the ters interacting with intense laser pulses is dominated photoionization and electron scattering cross-section. by slow electrons (orange area). The inset shows the Shape resonances have been the subject of numerous same spectrum on a logarithmic scale, indicating the studies, owing to the possibility to relate their positions slow electrons (indicated by the red curve) and the fast in energy to the internuclear distances. While a number electrons (indicated by the green curve). of correlations have been found, such assignments remain a subject of controversy [Pia99].

Our simulations showed that the slow electrons result Shape resonances have been recently identified to play from a two-step process, where the second step relies a key role in shaping the photoelectron momentum dis- on a final kick that has so far escaped the attention of tribution resulting from strong field ionization of mole- the scientific community. First, the intense laser pulse cules [ONL11]. In strong field ionization experiments, detaches electrons from individual atoms. These elec- an electron that results from tunnel ionization can be trons remain trapped in the cluster as they are strongly accelerated before being driven back to its parent ion attracted by the ions. When this attraction diminishes as by the oscillating laser field. Electron scattering in the the particles move farther away from each other during laser field is responsible for the appearance of arec- cluster expansion, the scene is set for the important sec- ollision plateau in the photoelectron momentum distri- ond step. Therein, weakly bound electrons collide with bution. Similar to electron impact experiments, a shape a highly excited ion and thus get a final kick that allows resonance is characterized by a broad increase of the them to escape from the cluster. laser-assisted electron scattering cross-section.

56 In recent investigations, we recorded the photoelectron Schwinger variational method using the ePolyScat soft- momentum distribution resulting from strong field ioniza- ware suite developed by Lucchese et al. [GLS94]. Our tion of I2 at 1.3 μm. At the equilibrium bond length, a result shows that laser-assisted electron-molecular-ion strong backscattered photoelectron emission at a low scattering is very sensitive to the dynamics of the shape kinetic energy is observed and assigned to a molecular resonance, and provides a novel means to investigate shape resonance (see Fig. 5). The dependence of the photoinduced molecular dynamics with high temporal properties of the shape resonance (i.e. its energy and and spatial resolution. linewidth) on the I-I internuclear distance was directly investigated by monitoring the change of the back- Molecular movie of ultrafast coherent rotational dynamics scattered photoelectrons as the internuclear distance of the molecule was varied in a controlled manner by Visualizing nuclear motion during molecular dynamics exciting a vibrational wavepacket in the B-state. As the at the relevant timescale represents a great challenge. molecular bond length elongates, the broad resonance The development of x-ray free electron lasers (FELs) observed in the backscattered photoelectrons appears and of ultrafast relativistic electron guns has recently al- to be shifted towards lower energy (see Fig. 5). Our lowed to make a molecular movie of the coherent vibra- finding is well reproduced by quantum calculations in tional motion of gas-phase iodine [GNC16] and of the which the electron-molecule scattering cross-section is dissociation dynamics of photoexcited CF3I [YZW18]. evaluated by solving the Schrödinger equation with a Despite this recent progress, the limited availability of beamtimes at these highly competitive user facilities, especially when femtosecond pulses are required, is a Experiment b Simulation currently limiting the investigation. 9 19 8 7 17 6 15 5 4 13 3 2 11 Recollision energy [eV] 1 110 130 150 170 110 130 150 170 Angle [Deg] Angle [Deg]

c Experiment d Simulation 8 19 6 4 17 2 15 0 -2 13 -4 Fig. 6:

Recollision energy [eV] -6 11 Molecular rotational clock; time-dependent O+ ion mo- -8 110 130 150 170 110 130 150 170 mentum distributions resulting from strong field ionization Angle [Deg] Angle [Deg] of rotationally excited OCS by 1.8 μm laser pulses. The rotational clock is shown over a full rotational period, with Fig. 5: π corresponding to half the rotational period. At 0, the a) Two-dimensional map of the rescattered electron angular confinement of the O+ ions along the vertical axis distribution extracted from the photoelectron momentum indicates a strong alignment of the molecule. A rich an- distribution recorded following strong field ionization of gular structure is observed at intermediate times. 13 2 I2 by a 1.3 μm pulse at an intensity of 4.6 x 10 W/cm . The strong backscattered electron emission at 180° is assigned to a shape resonance and is well reproduced As an alternative, laser-based techniques have been by a quantum calculation (b). (c) Difference between the proposed that rely on strong field ionization of mole- rescattered electron distributions extracted from experi- cules. For instance, in a Coulomb explosion imaging ex- ments when the vibrational wavepacket reaches the periment, ultrafast molecular dynamics can be directly inner (R = 2.78 Å) and outer (R = 3.68 Å) turning points inferred from the angle and kinetic energy distribution and (d) calculated using EpolyScat. In this map negative of the outgoing ions that are formed by strong field ion- values (plotted in blue) mean that the contribution at a ization. While the ion kinetic energy distribution provides particular recollision energy and angle is more prominent a direct measurement of the internuclear distances, at the outer turning point, whereas a positive value (red the photoemission angle allows retrieving the relative color) means that the contribution is more prominent at position of the atoms in the molecule. The dissociation the inner turning point. The two extrema observed at and vibrational wavepacket dynamics of I2 and more re- 180° can be directly related to the shift of the shape reso- cently, the torsional motion in an axially chiral biphenyl nance to lower energy when the bond length increases. derivative [CNB14] have been characterized by time-resolved Coulomb explosion imaging.

57 In a recent investigation, we have exploited this tech- personic beam have been detected using a reaction mi- nique to make a high resolution movie of the ultrafast co- croscope. This scheme allowed a correlated detection of herent rotational dynamics of OCS. Us ing a sequence all charged particles formed in the laser beam focal spot of two femtosecond laser pulses with appropriate time on an individual basis. delay and intensity ratio, a rotational wavepacket was formed in an ensemble of quantum-state selected OCS Fig. 7 shows a time of flight (TOF) spectrum of photo- obtained by cold molecular expansion and Stark deflec- ions relative to the TOF of a photoelectron detected to- tion. The time-dependent O+ ion momentum distributions gether with the respective ion. It reveals the presence of resulting from Coulomb explosion imaging of the mole- the strong-field water dimer single ionization and frag- cule by 1.8 μm laser pulses were used to directly image mentation processes: the time evolution of the angular probability distribution + of the molecule during rotational motion. An unprece- (H2O)2 (H2O)2 + e 2 dented degree of field-free alignment of = + 0.95 was obtained at the revivals of the rotational wave- (H2O)2 (H3O) + OH + e packet, whereas in between a very rich angular dynamics was observed with very high resolution (see Fig. 6), We were not able to identify the unprotonated dissocia- from which the complete wavepacket could be uniquely tive ionization channel reconstructed and reproduced with calculations based + on solving the time-dependent Schrödinger equation for (H2O)2 (H2O) + (H2O) + e a rigid rotor in interaction with a pulse sequence [KRM]. + because the corresponding H2O TOF overlapped with Proton transfer following strong-field ionization of the the water ion TOF from ionization of background gas + water dimer water monomers. The presence of (H3O) in the TOF spectrum unambiguously shows proton transfer oc- Hydrogen-bonded systems have attracted considerable curring after strong-field single ionization of (H2O)2. interest owing to their important role for the existence of life, chemical reactions and atmospheric science. The water dimer (H2O)2 is one of the simplest of these 2 10102 systems. Many investigations on proton transfer have 43200 chosen it as the model molecule. In the liquid phase, the 1010 (ns) 2 [ns] 2 transfer of a proton between water molecules proceeds +t 1 1 t 1 +t 43100 (b) on an ultra-fast time scale, which has been estimated 1 t from experiments and calculations to be less than 100 fs 1950019500 20000 2050020500 2100021000 [GPM90] or even 50 fsec [FDH06]. However, there are t1 (ns) t1 [ns] insufficient experimental data available to date since a + direct identification of the H3O ion in the liquid phase has remained ambiguous. Fig. 8: The TOF sum of ion pairs plotted over the TOF of the + first ion reaching the ion detector. Pairs of 2H O ions from ++ Coulomb explosion of (H2O)2 contribute to the central,

) 16 + 16 + s intense group of ion pairs on the black horizontal line. t (H O) H2 O 2 2 n ×100 + + u 16 + M=36.031 Coulomb explosion into H3O and OH after proton trans-

o 36 + H3 O 20 + Ar C 40 ++ ( Ar Ne M=35.968 fer gives rise to the ion pair accumulation points to the d 17 + l H O 18 + e 2 i H2 O left and right of the central spot (connected by the red Y Yield [Counts] Yield horizontal line). 220.80.8 221.61.6 22.422.4 29.629.6 30.430.4 ti − te (μs) ti – te [µm]

Besides single ionization we also observed double ion- Fig. 7: ization of the dimer, where successively one electron is Ion TOF spectrum relative to the TOF of the accompany- removed from the proton donor and acceptor sites of ing photoelectron taken at a laser pulse peak intensity of the dimer. This doubly charged dimer decays via Cou- 14 2 + 1.2 x 10 W/cm . Clearly identifiable are H2O ions from lomb explosion. We found two explosion channels, one + + + water monomer ionization, stable water dimer ions and into two H2O ions and one into an H3O and an OH + H3O ions formed after proton transfer and dissociation ion. These two explosion channels are clearly identifi- + of (H2O)2 . able in Fig. 8. In this figure the TOF sum of ion pairs is shown plotted over the TOF of the first ion reaching the + ion detector. Pairs of H2O ions from Coulomb explosion ++ We investigated the proton transfer in isolated singly of (H2O)2 contribute to the central, most intense group + ionized water dimers [ZLF]. The transfer was triggered of ion pairs, whereas Coulomb explosion into H3O and + by strong-field ionization of (H2O)2 dimers present in a OH after proton transfer gives rise to the ion pair accu- supersonic beam seeded with water molecules at a light mulation points to the left and right of the central spot intensity of 1.2 x 1014 W/cm2. The Ti:Sapphire laser puls- (connected by the red horizontal line). This correlation es employed had a pulse width of 38 fs at a wavelength plot shows that proton transfer within the time interval of 780 nm. Photoions and electrons emerging from the when the laser pulse is applied happens in the singly strong-field interaction of the laser pulses with the su- charged dimer ion before double ionization. From the

58 + ion correlation plot (Fig. 8) a branching ratio R = 0.081 ensuing two-body breakup into NO2 and NO2 is then into protonated and unprotonated Coulomb explosion probed by SFI with the probe pulse, resulting in a de- can be extracted. lay-dependent Coulomb repulsion.

We used this branching ratio to derive a rate constant for An analogous plot to Fig. 9, focusing on the coinci- + proton transfer after strong-fi eld single ionization of wa- dent appearance of two NO2 ions, displays bands (i) ter dimers. This was done by employing a rate equation and (iii) and a strong suppression of band (ii), in line approach to analyze the observed two step double ion- with the interpretation given above. When combined ization [ZLF]. Based on this approach we were able to with computed intermolecular potential energy surfac- -1 deduce a proton transfer rate constant of rpt = 0.032 fs es, the experimental data allow the extraction of the for the water dimer ion. It amounts to a time constant intermolecular bond length at the inner turning point of τpt = 1/rpt = 31 fs for the proton transfer. This time con- the vibration as well as the vibrational amplitude. stant compares favorably with molecular dynamics calculations of the time it takes for the proton transfer after ionization (H2O)2 which ranges between 25 fs and 100 fs Counts counts [SHO13, Tac11]. V ]

[ e 3 k i n E Probing NO2 dimer intermolecular vibration with coinci- 2.5 dence velocity mapping 2 [eV]

kin 1.5

The intermolecular vibration of the NO2 dimer molecule E is an interesting object of study for high-harmonic gener- 1 ation and strong-fi eld ionization probes of molecular dy- 0.5 namics [LZL08]. The vibration can be conveniently excited by impulsive stimulated Raman scattering (ISRS). -800 -600 -400 -200 0 200 400 600 800delay [fs] Important for those investigations is a determination of Delay [fs] the amplitude of the intramolecular vibrational motion.

Here we study vibrating O2N-NO2 molecules with co- Fig. 9: + incidence photofragment kinetic energy spectroscopy. Experimentally measured kinetic energy of NO2 frag- The ISRS pump and the strong-fi eld ionization (SFI) ments (in eV) as a function of the delay (in fs) between probe pulses were provided by an in-house built, high the ISRS pump pulse and the SFI probe pulse. Three repetition rate OPCPA system [FGM16], delivering 7 dominant features are observed and can be assigned as fs duration pulses at 800nm central wavelength and a described in the text. repetition rate of 400 kHz. Ions were recorded with a novel velocity map imaging (VMI) spectrometer based on an in-vacuum pixel detector [LFD17]. The solid-state T4: Quantum dynamic in tailored fi elds Timepix detector technology, developed by the Medipix collaboration at CERN [MED], allows the recording of Generation and characterization of highly elliptic atto- the spatial position of ion impact together with the ion second pulses arrival time. While the spatial resolution is comparable or superior to that of conventional delay-line anode de- The availability of circularly polarized attosecond pulses tectors, the inherent time resolution of the Timepix chip in the form of isolated pulses and pulse trains (APTs), is currently still somewhat limited. Nonetheless, as we which would enable attosecond-resolved measure- demonstrate here, it is suffi ciently high to enable studies ments of chiral-sensitive electron dynamics, remains which distinguish the coincident appearance of certain both a challenging and important task. We describe a ionic species in SFI processes. way to generate harmonics with a chiral spectrum supporting highly elliptic APTs and enabling smooth control + Fig. 9 displays the kinetic energy of NO2 fragments as of their ellipticity from linear to almost circular using a a function of the delay between the strong-fi eld ISRS two-color, bi-circular driver approach. We show exper- pump pulse (intensity 8 x 1012 W/cm2) and the SFI probe imentally that control over phase matching through the pulse (intensity 2 x 1013 W/cm2). Three features are ob- position of the laser beam focus relative to the gener- served: (i) At a kinetic energy of 2.4 - 2.8 eV, a band ating neon gas cell, combined with the proper choice is observed originating from double ionization and Cou- of the intensities of the two driving laser fi elds, offers lomb explosion of the vibrationally excited dimer (NO2)2 an excellent control knob over the relative intensities of + + producing NO2 +NO2 . (ii) At low kinetic energy (0.1-0.5 harmonics of 3n+1 versus 3n+2 orders, thus providing eV), the observed band originates from dissociative an effi cient helicity fi lter. The resulting APTs reconstruct- single ionization of vibrationally excited (NO2)2 to the Ag ed from the generated chiral spectra correspond to an + + state of (NO2)2 producing NO2 +NO2. The average ki- ellipticity as high as ε = 0.75. netic energy in bands (i) and (ii) is found to oscillate in phase as a function of pump-probe delay, indicative of We have used a Ti:sapphire based laser system with a the intermolecular vibration at 7.7 THz. A third band (iii) single stage regenerative amplifi er producing 35 fs puls- displays a kinetic energy which exponentially decreases es with up to 4 mJ energy and central wavelength of with time-delay. It is attributed to SFI of the neutral frag- ∼ 795 nm at 1 kHz repetition rate. The carrier envelope + ment by the pump pulse, producing excited (NO2)2 . The phase of the pulses was not locked. The laser beam

59 was directed into the optical setup shown in Fig. 10. The the orders 3n+1 right- and the orders 3n+2 left-rotating original beam was split into two beams with 70/30 ratio. corresponding to the “red” and the “blue” driving beams. The first, stronger, beam was sent onto a 0.1 mm, thin Fig. 11 presents the dependence of the recorded har- beta-barium borate (BBO) crystal to generate a second monic spectra on the z-distance from the focal plane to harmonic at ∼ 400 nm with a pulse energy up to 0.8 mJ. the center of the gas cell where the harmonics are gen- The second, weaker beam remains at the fundamental erated, with positive z meaning the laser beam waist wavelength of 795 nm with a pulse energy up to 1.0 mJ. is positioned in front of the cell. The observed spectra We also can smoothly tune the energies of the two puls- are strongly cell-position dependent, with a steadily es and the ratio between them by changing the original growing difference in the intensities of the right- and the input pulse energy and by using a reflective attenuator. left-rotating harmonics as the cell is shifting from neg- Both beams passed through achromatic broadband λ/2 ative towards positive z. The intensity ratios I3n+1/I3n+2 of and λ/4 waveplates, yielding nearly circular polarization the lines of the four most visible harmonic pairs located (ellipticity ε ≈ 0.95) with clockwise (right-rotating) heli- around 30 eV (H19 and H20), 35 eV (H22 and H23), city for the “red” and counter-clockwise (left-rotating) 40 eV (H25 and H26), and 45 eV (H28 and H29) are helicity for the “blue” beams. The fundamental and the slightly different for the listed harmonic pairs, but with second-harmonic beams were combined in collinear ge- the same tendency: the ratio achieves its maximum val- ometry and focused with a single Ag mirror at f/100 into ue of about 8 when the cell is located at the terminal a 2-mm-long gas cell containing Ne. The cell holder was positive position. fixed on a micrometer translation stage, allowing us to move the cell along the propagation z axis.

20 25 30 35 40 45 50 55 60 1.0 0.8 0.6 0.4 0.2 Intensity [a. u.] 0.0

3.5

0 Cell position [mm] -2

Fig. 10: Schematic setup for HHG by tailored laser pulses. BBO: -3.5 beta-barium borate crystal for generation of the laser beam’s second harmonic; MCP: detector for XUV radia- 1.0 0.8 tion; BS: beam splitter. 0.6 0.4 0.2

Intensity [a. u.] 0.0 The laser beam intensities in the gas cell at z = 3.5 mm 20 25 30 35 40 45 50 55 60 14 2 (see Fig. 11) were estimated to be I(ω) ≈ 4.3×10 W/cm Photon energy [ev] and I(2ω) ≅ 4.1×1014 W/cm2. The cell was initially sealed with a metal foil which was then burned through by the laser beams at the start of the experiment. The resulting Fig. 11: cell opening d0 ≅ 60 μm was similar to the focal spot size, High harmonics generated as a function of the gas allowing us to keep the gas pressure inside the cell at cell position z relative to the laser beam waist. The up- ≈ 40 mbar and the vacuum inside the surrounding inter- per and lower 1D harmonic spectra have been taken at −3 action chamber at a level of Prest ≈ 10 mbar. After pass- z = +3.5 mm and -3.5 mm, respectively. The calculated ing the gas cell, the driving laser beams were blocked ellipticity of the combined XUV field is noted on the right by a 200 nm thick aluminum foil. The transmitted XUV hand side of the figure. radiation was directed towards an XUV spectrometer. The generated, spectrally resolved XUV radiation was detected by a microchannel plate (MCP)-based XUV The larger the difference in the emission of 3n+1 right- detector equipped with a phosphor screen and recorded versus 3n+2 left-circularly polarized high harmonics, the by a fast CMOS camera (PointGrey). larger is the ellipticity of the generated APT. Our experimental results also clearly demonstrate the important The generated XUV spectra in Fig. 11 show the typical role of phase matching in the studied experimental ge- shape expected for the bi-chromatic approach. The har- ometry. The main difference of our geometry compared monics of orders 3n are strongly suppressed, and the al- to hollow waveguide setups are the prominent effects lowed harmonics are generated circularly polarized with of the Gouy phase and of the atomic or intrinsic phase.

60 The phase mismatch Δk between the wave-vector of the driving composite (ω+2ω) field kL and the q-th (q=3n+1; 0 3n+2) harmonic kq can be written as: 3 -1 2 Δkq = kL−kq = ΔkN + Δke + Δkf + Δkat. -2 1 Here ΔkN and Δke denote phase mismatch due to the 0 -3 [a. u.] neutral gas and free electrons, respectively. Δkf de- y notes the contribution of the geometrical phase shift P -1 -4 that arises from the focusing conditions. The atomic or -2 -5 intrinsic phase mismatch Δkat is related to the electron -3 -6 excursion time between ionization and recombination -3 -2 -1 0 1 2 3 and is larger for the long electron trajectories. For the Px [a. u.] two cell terminal positions, where the difference in the observed asymmetry is the highest, the beam and field 3 0 parameters are equal. Hence, the contributions from 2 -1 ΔkN , Δke are the same. The change in Δkf associated 1 with the Gouy phase is symmetric and positive, but the -2 0 change of Δkat depends on the transverse intensity pro- -3 [a. u.] file and is anti-symmetric with respect to the position of y -1 P -4 the gas cell relative to the focal plane, thus changing its -2 sign from positive to negative. A partial compensation -5 of the atomic polarization phase by the Gouy phase -3 eliminates the so-called “long trajectories” in the high -6 -3 -2 -1 0 1 2 3 harmonic generation process. While the importance of long trajectories in the bi-circular scheme is substan- Px [a. u.] tially less than in the case of linearly polarized drivers, it nevertheless remains non-negligible, and their removal Fig. 12: is beneficial for a high contrast of the 3n+1 and 3n+2 False-color plot in the electron-momentum plane of the harmonic lines. logarithm of the differential ionization rate (in a.u.) of neon by a bicircular ω-2ω driving field with counterrotat- We have demonstrated that a combination of a medium ing polarizations and equal intensities of the two com- 14 2 position of the harmonic generating cell and of suitably ponents (I1 = I2 = 2 x 10 W/cm ) and ω = 1.55 eV. The chosen intensities of the fundamental and second-har- calculation includes the direct and the rescattering term monic driving laser fields creates an effective helicity-de- of the SFA. Direct electrons govern the central triangular pendent filter and offers a simple and practical possibili- part. Where present, they mask the rescattering contribu- ty to tune the ellipticity of attosecond pulses in a smooth tions. Rescattered electrons are responsible for the outer and predictable way. The reported tunable ellipticity with (near-circular) parts. up to ε = 0.75 is crucial for numerous applications, and we believe will open a way for new methods to explore chiral phenomena

Atomic processes in bicircular fields: Helicity asymmetry 3 0.8 2 0.6 Bicircular fields, i.e., the superposition of two circular- 0.4 1 ly polarized fields co- or counterrotating with different 0.2 frequencies in the same plane, have become a power- 0 0 [a. u.] ful and versatile tool in strong-field physics, with many y -0.2 P -1 applications from the generation of bright circularly po- -0.4 larized high-order harmonics to chiral recognition and -2 -0.6 discrimination. Here we present an example of how -3 -0.8 bicircular fields can be utilized for the analysis of the angle-dependent energy spectrum of above-threshold -3 -2 -1 0 1 2 3 ionization (ATI). The frequently used quantum-mechan- Px [a. u.] ical strong-field approximation (SFA) represents the ATI transition amplitude in the form of a power series in the Fig. 13: electron-core potential. In its lowest-order term, the lib- False-color plot of the helicity-asymmetry parameter A(p) erated electron does not interact with the core any more for the bicircular counterpropagating driving field un- after the instant of ionization (direct electrons). The next- derlying Fig. (12). Large values of A(p) indicate that the to-lowest-order term allows for exactly one such inter- corresponding region is mostly populated by rescattered action (rescattered electrons), etc. an experiment, or a electrons. Little asymmetry is visible for small |p|, since in numerical solution of the time-dependent Schroedinger this region direct electrons are dominant, which have no equation (TDSE), does not allow for such a distinction. helicity asymmetry. However, being able to label an electron as direct or rescattered or caused by interference of one with the other

61 greatly helps with the physical interpretation. With the Mil18c: D. B. Milošević; Phys. Rev. A 98 (2018) 053420 help of ATI spectra recorded for bicircular fields with opposite helicities such a distinction can be inferred from NKS18: C. Neidel et al.; Chem. Phys. 514 (2018) 106 the data. PAR18: G. Porat et al.; Nat. Comm. 9 (2018) 2805 Figure 12 exhibits ATI spectra calculated from the first two terms of the SFA Born-like series for a bicircular field SBS18a: F. Schell et al.; Science Advances 4 (2018) (upper panel) and for the same field with opposite he- eaap8148 licities (lower panel). Both velocity maps are invariant upon rotations by multiples of 120 deg, which reflects SBS18b: F. Schell et al.; Phys. Chem. Chem. Phys. 20 the trefoil shape of a parametric plot of the bicircular (2018) 14708 driving fields. The central (triangular) parts of the two velocity maps are the same in both panels, but the outer SPA18: B. Schütte et al.; Phys. Rev. Lett. 121 (2018) parts differ. The central parts obey reflection symmetry 63202 about three axes at 60, 180, and 300 deg. This is broken by the outer parts. The central parts are due to the ZFR18: C. Zhang et al.; Phys. Rev. A 97 (2018) 023417 lowest-order term of the Born series (“direct electrons”) while the outer parts come from the first-order term (res- ZMK18: H. Zimmermann et al.; Phys. Rev. Lett. 120 cattered electrons). (2018) 123202

Comparison of the two velocity maps is facilitated by plotting the asymmetry parameter, defined as the difference over the sum of the two maps, A(p) = [w+(p) Own Publications submitted – w-(p)] / [w+(p) + w-(p)], which is displayed in Fig. 13. As expected, the central region shows little or no asym- KRM: E. T. Karamatskos et al.; Nat. Comm. metry, while in the outer region it is very pronounced. MBe: D. B. Milosevic, W. Becker; Phys. Rev. A The power of this method will become apparent once it is applied to spectra which are not calculated from the ZLF: C. Zhang et al.; Phys. Rev. A SFA, but instead obtained from experiment or the TDSE. In those situations, it is far from clear whether a certain feature of the velocity map should be attributed to the direct ionization pathway or to rescattering. This question Other Publications can be answered by inspection of a plot of the helicity asymmetry parameter of two spectra taken with bicircu- CNB14: L. Christensen et al.; Phys. Rev. Lett. 113 lar fields of opposite helicities [GBM18]. A general pre- (2014) 073005 sentation of the symmetries of bicircular angle-resolved ATI spectra can be found in [GBH18]. ENR09: U. Eichmann et al. ; Nature 461 (2009) 1261

FDH06: A. Furuhama et al.; J. Chem. Phys. 124 (2006) 164310

Own Publications 2018 ff FGM16: F. Furch et al.; Optics Express 24, 19293 (2016) (for full titles and list of authors see appendix 1) GLS94: F. A. Gianturco et al.; J. Chem. Phys. 100 (1994) BGM18: W. Becker et al.; J. Phys. B: At. Mol. Opt. Phys. 6464 51 (2018) 162002 GNC16: J. M. Glownia et al.; Phys. Rev. Lett. 117 (2016) GBH18: A. Gazibegović-Busuladžić et al.; Phys. Rev. A 153003 97 (2018) 043432 GPM90: Y. Gauduel et al.; Chem. Phys. 149 (1990) 1 GBM18: A. Gazibegović-Busuladžić et al.; Optics Ex- press 26 (2018) 12684 ILB18: H. Ibrahim et al.; J. Phys. B 51 (2018) 042002

JZA18: Á. Jiménez Galán et al.; Phys. Rev. A 97 (2018) LFD17: J. Long et al.; J. Chem. Phys. 147 (2017) 013919 023409 LZL08: W. Li et al.; Science 322 (2008) 1207 KWF18: F. Krecinic et al.; Phys. Rev. A 98 (2018) 041401 MED: Medipix Collaboration CERN, URL: http://medipix. MBe18a: D. B. Milošević, and W. Becker; J. Phys. B: At. web.cern.ch/ Mol. Opt. Phys. 51 (2018) 054001 MNG09: B. Manschetus et al.; PRL 102, (2009) 113002 Mil18a: D. B. Milošević; Phys. Rev. A 97 (2018) 013416 NGS08: T. Nubbemeyer et al.; PRL 101 (2008) 233001 Mil18b: D. B. Milošević; Phys. Rev. A 98 (2018) 033405

62 ONL11: M. Okunishi et al.; Phys. Rev. Lett. 106 (2011) 063001

Pia99: M. Piancastelli; J. Elec. Spec. Rel. Phen. 100 (1999) 167

SHO13: O. Svoboda et al.; Phys. Chem. Chem. Phys. 15 (2013) 11531

Tac11: H. Tachikawa; Phys. Chem. Chem. Phys. 13 (2011) 11206

YZW18: J. Yang et al.; Science 361 (2018) 64

ZEi16: H. Zimmermann et al.; Phys. Scr. 91 (2016) 104002

ZIv17: N. Zhavoronkov et al.; Optics Letters 42 (2017) 4720

ZPI17: H. Zimmermann et al.; Phys. Rev. Lett. 118 (2017) 013003

Invited Talks at International Conferences (for full titles see appendix 2)

W. Becker; 27th Annual International Laser Physics Workshop (LPHYS'18) (Nottingham, UK, 2018-07)

U. Eichmann; 27th annual International Laser Physics Workshop (LPHYS'18) (Nottingham, UK, 2018-07)

U. Eichmann; Thomas F. Gallgher retirement symposium (University of Virginia, Charlottesville, USA, 2018- 08)

U. Eichmann; International Workshop on Atomic Phys- ics 2018 (Max Planck Institute for the Physics of Com- plex Systems, (Dresden, Germany, 2018-11)

J. Mikosch; Quantum Dynamics in Tailored Intense Fields (QUTIF), (Hamburg, Germany, 2018-02)

J. Mikosch; DPG Spring Meeting 2018, (Erlangen, Ger- many, 2018-03)

C. P. Schulz; Gordon Research Conference on Multi- photon Processes (Smithfield, RI ,USA, 2018-07)

C.P. Schulz; 27th annual International Laser Physics Workshop (LPHYS'18) (Nottingham, UK, 2018-06)

63 3.1: Dynamics of Condensed Phase Molecular Systems

E. T. J. Nibbering, O. Kornilov (project coordinators) and N. Acharyya, E.-M. Brüning, M.-A. Codescu, F. Dahms, M. Ekimova, B. P. Fingerhut, J. Hummert, E. Ikonnikov, C. Kleine, A. Kundu, J. Lebendig-Kuhla, J. Ludwig, A. Lübcke, N. Mayer, M. Oßwald, G. Reitsma, M. Richter, H.-H. Ritze, J. Schauss

1. Overview 3. Results in 2018

This project aims at a real-time observation of ultrafast T1: Hydrogen bond dynamics in hydrated biomimet- molecular processes in the condensed phase, address- ic and biomolecular systems (DFG FI 2043/1-1) ing the dynamics of elementary excitations, photoinduced chemical reactions and ultrafast changes of the Biomimetic and biomolecular systems and their inter- electronic and/or chemical structure of molecular sys- actions with water and counter ions are studied to un- tems. The project makes use of a broad range of ex- ravel the couplings between the molecular systems perimental techniques including all-optical pump-probe and the fluctuating water shells in the electronic ground spectroscopy in a range from the ultraviolet to mid-infra- state. Hydration dynamics of RNA and DNA oligomers red, infrared photon-echo and multidimensional vibra- [BSS18, FBS], native salmon DNA in thin films and solu- tional spectroscopies, and photoelectron spectroscopy tion, and of dimethylphosphate ions as DNA model sys- using ultrashort VUV, XUV, and soft-X-ray pulses. tems [SDF19] are the main topics in recent years. A second research line is the investigation of the vibrational dynamics and relaxation of the hydrated proton [KDF18, DKP]. The experiments are based on ultrafast two-color 2. Topics and collaborations infrared (IR) pump-probe and multi-dimensional photon echo spectroscopies, complemented by computational Research in this project has been structured into four methods such as density functional theory and ab initio major topical directions: molecular dynamics to simulate linear and multidimensional spectra. T1: Hydrogen bond dynamics in hydrated biomimetic and biomolecular systems The structure and dynamics of the RNA and DNA double helix are influenced in a decisive way by the surround- Collaboration partners: J. T. Hynes (University of Col- ing water shell and their counter ion atmosphere. In pre- orado, Boulder, USA), D. Laage (École Normale vious years we have introduced vibrational excitations Supérieure, Paris, France), S. Mukamel (University of of the sugar-phosphate DNA backbone as sensitive California at Irvine, USA), E. Pines (Ben Gurion Univer- probes of structural fluctuations, electric fields exerted sity of the Negev, Beer-Sheva, Israel). by the water shell, and local hydrogen bond structure. Another important aspect involves possible differences T2: Transient structure determination of hydrogen in the hydration shells of RNA and DNA. In pump-probe bonded acid-base pairs and femtosecond two-dimensional infrared (2D-IR) photon-echo experiments performed with (AU)23 RNA Collaboration partners: M. Odelius (Stockholm Univer- and (AT)23 DNA oligomers, respectively, the vibrational sity, Sweden), Ph. Wernet (Helmholtz Zentrum Berlin, response of the sugar-phosphate backbone has been Germany), N. Huse (University of Hamburg). mapped in a temporally and spectrally resolved way [BSS18]. The backbone vibrations in a frequency range T3: Charge transport in biomimetic and biological from 900 to 1300 cm-1 display a partly ordered structure systems for RNA compared to DNA which is reflected in additional bands along the frequency diagonal ν1=ν3, reduced Collaboration partners: V. S. Batista (Yale Universi- inhomogeneity and a more complex distribution of off-di- ty, New Haven, CT, USA), D. Sebastiani (Martin-Lu- agonal peaks in the 2D-IR spectra (Figure 1). Such a ther-University Halle-Wittenberg, Germany). structured water arrangement around RNA is mediated by the coupling to the 2’-OH group of the sugar units T4: Electronic excited state dynamics in molecular (Figure 2) as has been revealed in detailed simulations model systems that allow for the first complete and quantitative identification of the different vibrations of the RNA backbone. Collaboration partners: O. Rader (Helmholtz Zen- trum Berlin), D. Arbi (University of Buenos Ayres), L. The stabilization of the macromolecular structures of Banares (Compulensa University, Madrid), W. Zinth DNA and RNA requires a compensation of strong repul- (Ludwig-Maximilians-Universität München, Germany), sive electric forces between the equally charged phos- B. Kohler (Ohio State University, Ohio, USA). phate groups by ions of opposite, i.e., positive charge. In this context, magnesium (Mg2+) ions are particularly Internal collaboration with Projects 2.3 and 3.3 has been relevant as Mg2+ ions not only stabilize the structure but established. changes of macromolecular structure via dynamic folding processes are connected with a rearrangement of posi

64 1030 1050 1070 1090 1110 1130 1130

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1030 0 1130

11110

-1.0 1250

Excitation frequency 1090

1070 1200 1050 ] -1 1030 [cm

1030 1050 1070 1090 1110 1130 1

-1 ν 1150 Detection frequency ν3 [cm ]

1250

Fig. 1: Comparison of RNA (top) and DNA (bottom) 2D-IR

spectra in the range around the symmetric (PO2)− 1200 −1 Excitation frequency stretching transition at ν3 ≈ 1090 cm . The RNA spectrum displays a subset of additional diagonal and cross peaks as well as different lineshapes of diagonal peaks. 1150 1150 1200 1250 -1 Detection frequency ν3 [cm ]

Fig. 3: Top: Molecular structure of a contact ion pair consisting of dimethylphosphate (DMP) and a magnesium ion Mg2+ embedded in water. The arrows mark the elonga- tions of the phosphorus-oxygen bonds in the asymmet- - ric (PO2) stretching vibration. Bottom: Two-dimensional - infrared (2D-IR) spectra of the asymmetric (PO2) stretching vibration measured at a waiting time T=500 fs after vibrational excitation. The vibrational response Fig. 2: is shown as a function of the infrared excitation and the Left: Structure of an RNA double helix, the blue spheres detection frequencies and consists of a component P1 represent sodium counterions. Right: Enlarged segment from DMP molecules without a magnesium ion in the of the phosphate-sugar backbone of RNA, including neighborhood and the contribution P2 from contact ion bridging water molecules and coordination to the 2’-OH pairs. The latter is shifted to higher frequencies due to - 2+ group of the sugar unit. the interaction between (PO2) and Mg . tive Mg2+ ions embedded in the surrounding water shell. microscopic density functional theory modelling of The relevance of different solvation geometries and the cluster geometries and associated spectroscopic fea- underlying interactions was studied in a proof-of-prin- tures, providing a spatial assignment of the observed ciple experiment for the dimethylphosphate anion, an 2D-IR signatures. The in-depth theoretical analysis established model system for the DNA and RNA back- shows that the subtle balance of attractive electro- bone and its interactions with hydrated Mg2+ [SDF19]. static (Coulomb) forces and repulsive forces due to 2D-IR spectroscopy enables to map Mg2+ ions in con- the quantum-mechanical exchange interaction gov- tact with the phosphate groups via a distinct blue-shift- ern the frequency position of the phosphate vibration. ed signature in the 2D spectrum (Figure 3). Data for The ability of 2D-IR spectroscopy to characterize the different Mg2+ concentrations have been analysed by short-ranged phosphate-ion interaction in solution pro-

65 Fig. 4: 1.0 1.0 (left) N K-edge spectra of

alkylamines EtxNH3-x (x=0..3) 0.5 0.5 in ethanol. To emphasize the 0.0 0.0 changes in spectral features 1.0 1.0 upon consecutive exchange of N-H for N-Et groups, for each 0.5 0.5 alkylamine EtxNH3-x (x=1..3), the

0.0 0.0 spectrum of Etx-1NH4-x (x=1..3) is 1.0 1.0 shown as grey line in the panels 0.5 0.5 as well. (right) N K-edge spec- + tra of alkylammonium EtyNH4-y 0.0 0.0 1.0 1.0 (y=0..4) chloride salts in water. To emphasize the changes in Normalised absorbance [arb. units] 0.5 0.5 Normalised absorbance [arb. units] spectral features upon consecu- 0.0 0.0 tive exchange of N-H for N-Et 400 405 410 415 420 1.0 groups, for each alkylammonium + Energy [eV] EtyNH4-y (y=1..4) chloride, the 0.5 + spectrum of Ety-1NH5-y (y=1..4) is 0.0 shown as grey line in the panels 400 405 410 415 420 as well. Energy [eV]

vides a non-invasive analytical tool that complements tronic structural dynamics at ultrafast time scales. The currently available structural techniques. An extension experimental results are analyzed in close collaboration of this new approach to DNA and RNA and their ionic with theory groups. environment is underway and expected to provide new insight in the forces stabilizing equilibrium structures In previous years, research activity has increasingly and driving folding processes. focused on the development of condensed phase soft- x-ray spectroscopy using liquid flatjet technology, using The vibrational energy redistribution and relaxation dy- either x-ray sources at beamlines of large scale facili- + namics of Zundel cations H5O2 in acetonitrile and neat ties, or lab-based table-top extreme high-order harmon- water have been studied by femtosecond infrared pump- ic radiation set-ups. We recently have successfully used probe spectroscopy with resonant excitation of the the table-top approach to measure soft-x-ray absorption 1200 cm−1 proton transfer mode [KDF18]. Transient spectra in transmission mode at the C and N K-edges of spectra in a range from 1000 to 2200 cm−1 reveal in- several solutes in aqueous solution [KEG] and refer to termode anharmonic couplings and a sub-100 fs decay the Research Highlight on this. of the proton transfer mode, followed by femtosecond vibrational redistribution within the vibrational manifold We have further expanded our activities on soft-x-ray of the Zundel cation and picosecond energy transfer to absorption spectroscopy at the UE52_SGM beamline the solvent. Energy transfer to an aqueous environment at HZB-BESSY II using our liquid flatjet system de- occurs on the same time scale as within neat water, signed for aqueous solutions, and have expanded this demonstrating the strong coupling of cations and water approach to samples dissolved in ethanol [EKO18, solvation shell. KGE18a, KGE18b].

We use N K-edge absorption spectroscopy to explore T2: Transient structure determination of hydrogen the electronic structure of the amine group, one of the bonded acid-base pairs most prototypical chemical functionalities playing a key (SAW-2016-MBI-1; ERC-2017-ADG “XRayProton”) role in acid–base chemistry, electron donor–acceptor interactions, and nucleophilic substitution reactions. In This activity aims at an analysis of the electronic struc- this study, we focus on aliphatic amines and make use of ture of hydrogen bonded acid-base pairs. By determin- the nitrogen 1s core electron excitations to elucidate the ing structure, the elementary chemical processes of roles of N–H σ* and N–C σ* contributions in the unoc- solvent-mediated proton release, transfer, and accep- cupied orbitals [EKO18]. We have measured N K-edge tance by the base will be elucidated most directly. Fem- absorption spectra of the ethylamine bases EtxNH3–x (x = tosecond infrared techniques can be applied to unravel 0...3; Et– = C2H5−) and the conjugate positively charged + the dynamics of particular hydrogen bonded groups. ethylammonium cation acids EtyNH4–y (y = 0...4; Et– = This information may be complemented by steady-state C2H5−) dissolved in the protic solvents ethanol and wa- and time-resolved methods ranging from NMR, FT-IR ter (Figure 4). Upon consecutive exchange of N–H for to X-ray absorption and emission spectroscopies. Ulti- ethyl-groups, we observe a spectral shift, a systematic mately the development of time-resolved X-ray spectro- decrease of the N K-edge pre-edge peak, and a major scopic techniques will enable the determination of elec- contribution in the post-edge region for the ethylamine

66 Fig. 5: LUMO orbitals of the

XA spectrum of EtxNH3-x (x=0..3) and the influence of hydrogen bonding.

NH3 XFH LUMO Accepting H-bond EtOH Donationg H-bond EtOH

(CH3CH2)NH2 XFH LUMO Accepting H-bond EtOH Donationg H-bond EtOH

(CH3CH2)NH2 XFH LUMO Accepting H-bond EtOH

series. Instead, for the ethylammonium ions, the con- servable for this d3(CrIII)–d4(MnIII)–d5(MnII) series is the secutive exchange of N–H for ethyl groups leads to an L-edge branching ratio, and we discuss it in comparison apparent reduction of pre-edge and post-edge intensi- to semiempirical multiplet theory and ab initio restricted ties relative to the main-edge band, without significant active space calculations [KGE18a, KGE18b]. frequency shifts. Building on findings from our previously reported study on aqueous ammonia and ammonium Using a transmission flatjet enables determining abso- ions, we rationalize these observations by comparing lute absorption cross sections and spectra free from calculated N K-edge absorption spectra of free and hy- X-ray-induced sample damage. On the basis of our ex- drogen-bonded clusters. Hydrogen bonding interactions perimental observations, we extrapolate the feasibility lead only to minor spectral effects in the ethylamine se- of 3d transition metal L-edge absorption spectroscopy ries, but have a large impact in the ethylammonium ion using the liquid flatjet approach in probing highly dilute series. Visualization of the unoccupied molecular orbit- biological solution samples and possible extensions to als shows the consecutive change in molecular orbital table-top soft X-ray sources. character from N–H σ* to N–C σ* in these alkylamine/ alkylammonium ion series (Figure 5). This can act as a benchmark for future studies on chemically more in- T3: Charge transport in biomimetic and biological volved amine compounds. systems (DFG NI 492/13-1) The 3d transition metals play a pivotal role in many charge transfer processes in catalysis and biology. X-ray In this topical area, elementary charge transport dynam- absorption spectroscopy at the L-edge of metal sites ics in solution are investigated from the viewpoint of their probes metal 2p–3d excitations, providing key access to functional role in biochemical processes. The objective their valence electronic structure, which is crucial for un- is to elucidate the underlying mechanisms for electron derstanding these processes. We report Mn L-edge ab- transfer, proton transfer as well as proton-coupled elec- II III sorption spectra of Mn (acac)2 and Mn (acac)3 as well tron transfer. This line of research builds on previous as the Cr L-edge absorption spectrum of high-spin chro- ultrafast studies of aqueous proton transfer using pho- III mium acetylacetonate Cr (acac)3 complexes in solution. toacids, as well as of photoinduced electron transfer in With this, we derive absolute absorption cross-sections donor-acceptor complexes. Experimental techniques for the L-edge transitions with peak magnitudes as large include transient UV/IR spectroscopy and photoelectron II III as 12 and 9 Mb for Mn (acac)2 and Mn (acac)3, respec- spectroscopy. tively. We critically assess how experimental absorption cross sections can be used to extract information on the Photoacids are organic molecules that upon electron- electronic structure of the studied system by compar- ic excitation exhibit a large jump in acidity and this has ing our results of this CrIII (3d3) complex to our previous been utilized to much effect in time-resolved studies of III work on L-edge absorption cross sections of Mn (acac)3 ultrafast proton transfer dynamics. A special class con- 4 II 5 (3d ) and Mn (acac)2 (3d ). Considering our experimen- sists of so-called bifunctional photoacids, where both tal uncertainties, the most insightful experimental ob- proton donating and proton accepting groups are part of

67 The major current activities are experiments employing the time delay compensated XUV monochromator

Mole fraction [D2O]: [CD3OD] beamline. Its performance in combination with a liquid jet endstation was demonstrated in the previous years. 4 3 The results on the dynamics of the yellow dye quino- 2 line yellow obtained and interpreted in the previous year 1 were published as the first experimental time-resolved 0 photoelectron spectroscopy of a solvated organic mol- Pulse -1 ecule [HRM18]. 6 delay [ps] 4 The work on the monochromator beamline continues 2 with investigation of photoelectron spectroscopy with 0 solvents other than water. The choice of solvents is -2 expanded to cover a broad polarity range from water, 4 ethanol, acetonitrile, tetrachloromethane, benzene, tol- 2 uene, to hexane. Building on the previous observation of photoelectron spectroscopy of tryptophan, the studies

Absorbance change [mOD] 0 of all major solvated amino acids were undertaken including concentration dependence of the photoelectron 3 spectra. The results of this study expectedly show sys- 2 tematic deviations of the electronic structure of amino 1 acids in solution from that in the gas phase reported in 0 the literature. -1 1400 1420 1440 1460 1480 1500 1520 The time-resolved data on relaxation dynamics of highly Wavenumber [cm-1] excited states in the naphthalene cation were analyzed. The relaxation times show a trend increasing with the photon energy of ionizing XUV radiation. Such behavior Fig. 6: is unexpected as it indicates that increase of the inter- Transient UV/IR pump-probe spectra of 7HQ in nal energy in the molecular cation does not speed up

[D2O]:[CD3OD] solvent mixtures showing the conversion its relaxation. However, taken together with the previ- from the neutral to the zwitterionic tautomer on picosec- ously published observation, that relaxation times also ond time scales with molar fraction ratios as indicated. increase with size of PAH molecules (naphthalene being the smallest member of the series) a conjecture could be formulated, that in highly excited PAH cations the same molecule. Bifunctional photoacids allow for a the relaxation is delayed due to a bottleneck effect at well-defined distance along which proton transport can the ground electronic state. Such quantum mechanical occur and – thus – defining a highly specific number of effect was also proposed earlier for the phenomena of solvent molecules that can function as solvent bridge threshold fragmentation and delayed ionization. The (for protic solvents such as water or methanol often de- experimental results accompanied by the conjecture of noted as ‘solvent wire’) through which the proton trans- delayed relaxation are currently under peer review. port is understood to occur either in concerted or sequential von Grotthuss-type fashion. The decay of electronically excited states of thymine and thymidine 5′-monophosphate was studied by time-re- Femtosecond UV/IR pump-probe experiments (Figure solved UV/vis and UV/IR spectroscopy and experimen- 6) and ab initio molecular dynamics calculations of 7-hy- tally determined spectral signatures were analyzed by droxyquinoline in water-methanol mixtures demonstrate quantum chemical calculations [PMC18]. In addition to - - an unexpectedly dominant OH /CH3O transport path- the well-established ultrafast internal conversion to the way but consistent with a solvent-dependent photoacidi- ground state, a so far unidentified UV-induced species ty free energy-reactivity correlation behaviour. was observed. This species decays with a time constant of 300 ps – 1 ns and is formed with a comparably high quantum yield of about 10 % independent of the sol- T4: Electronic excited state dynamics in molecular vent. The data indicate that the observed species is not model systems a precursor of the lowest 3ππ* state and that it decays (DFG KO 4920/1-1; DFG FI 2043/1-1; LU 1638/3-1) directly to the electronic ground state. Most importantly, the signature of the so far unidentified UV-induced spe- Determination of the ultrafast electronic excited state cies is not only observed for monomeric thymine bases, dynamics of organic molecules in solution is the main but is also present for all-thymine oligomers, thus being objective of this topical area. Photophysical events such a potential precursor to damage in DNA strands. as internal conversion, and photochemical transforma- tions, trans/cis isomerization, ring opening or closure Further activities in the project include collaboration with are examples of elementary processes to be studied in the Institute for Zoo- and Wildlife (IZW) research and detail [HRM18]. The experiments address investigation the Immunology institute of Free University of Berlin. of dynamics in electronically excited states with time-re- The topic of collaboration is the use of nonlinear laser solved photoionization methods. radiation for decontamination of cellular samples and

68 development of vaccines against common worm para- EHB: M. Ekimova, F. Hoffmann, G. Bekçioğlu-Neff, A. sites. With this collaborative project a plan of the first Rafferty, E. T. J. Nibbering, and D. Sebastiani; Ultrafast joint studies was developed and the idea was submitted proton transport in water-methanol mixtures; in Ultrafast as a patent application. The construction of a suitable Phenomena XXI bio/laser laboratory at IZW and proof-of-principle experiments are underway. FBS: B. P. Fingerhut, E. M. Bruening, J. Schauss, T. Sie- bert, and T. Elsaesser; Interactions of RNA and water probed by 2D-IR spectroscopy; in Ultrafast Phenomena XXI

Own Publications 2018 ff KEG: C. Kleine, M. Ekimova, G. Goldsztejn, S. Raabe, (for full titles and list of authors see appendix 1) C. Strüber, J. Ludwig, S. Yarlagadda, S. Eisebitt, M. J. J. Vrakking, T. Elsaesser, E. T. J. Nibbering, and A. BSS18: E. M. Bruening, J. Schauss, T. Siebert, B. Fing- Rouzée; Soft X-ray absorption spectroscopy of aque- erhut, and T. Elsaesser; Vibrational dynamics and cou- ous solutions using a table-top femtosecond soft X-ray plings of the hydrated RNA backbone – a 2D-IR study; source; J. Phys. Chem. Lett. J. Phys. Chem. Lett. 9 (2018) 583-587 SDF: J. Schauss, F. Dahms, B. P. Fingerhut, and T. El- EKO18: M. Ekimova, M. Kubin, M. Ochmann, J. Ludwig, saesser; Phosphate–magnesium ion interactions in wa- N. Huse, P. Wernet, M. Odelius, and E. T. J. Nibbering; ter probed by ultrafast two-dimensional infrared spec- Soft-x-ray spectroscopy of the amine group: hydrogen troscopy; J. Phys. Chem. Lett. bond motifs in alkylamine/alkylammonium acid-base pairs; J. Phys. Chem. B 122 (2018) 7737-7746

HRM18: J. Hummert, G. Reitsma, N. Mayer, E. Ikon- Invited Talks at International Conferences nikov, M. Eckstein, O. Kornilov, Femtosecond extreme (for full titles see appendix 2) ultraviolet photoelectron spectroscopy of organic molecules in aqueous solution, J. Phys. Chem. Lett. 9 (2018) T. Elsaesser; XVII. DESY Research Course 2018 - 6649-6655 Trends in Water Research (Hamburg, Germany, 2018- 02): Ultrafast hydration dynamics of protons and biomol- KDF18: A. Kundu, F. Dahms, B. P. Fingerhut, E. T. J. ecules mapped by two-dimensional infrared spectrosco- Nibbering, E. Pines, and T. Elsaesser; Ultrafast vibra- py tional relaxation and energy dissipation of hydrated excess protons in polar solvents; Chem. Phys. Lett. 713 T. Elsaesser; The 9th International Conference on Co- (2018) 111-116 herent Multidimensional Spectroscopy (CMDS) 2018 (Seoul, South Korea, 2018-06): Structure and dynamics KGE18a: M. Kubin, M. Guo, M. Ekimova, M. L. Baker, of hydrated excess protons in polar solvents mapped by T. Kroll, E. Källman, J. Kern, V. K. Yachandra, J. Yano, ultrafast 2D-IR spectroscopy E. T. J. Nibbering, M. Lundberg, and P. Wernet; Direct determination of absolute absorption cross sections at T. Elsaesser; Workshop on Advances of Multidimen- the L-edge of dilute Mn complexes in solution using a sional Vibrational Spectroscopy in Water, Biology and transmission flatjet; Inorg. Chem.57 (2018) 5449-5462 Materials Science (Telluride, CO, USA, 2018-07): Ultra- fast hydration dynamics of protons and biomolecules KGE18b: M. Kubin, M. Guo, M. Ekimova, E. Källman, mapped by 2D-IR spectroscopy J. Kern, V. K. Yachandra, J. Yano, E. T. J. Nibbering, M. Lundberg, and P. Wernet; Cr L-edge X-ray absorption T. Elsaesser; International Workshop on “Probing Bio- III spectroscopy of Cr (acac)3 in solution with measured logical Matter with and without Labels” (Freie Universität and calculated absolute absorption cross sections; J. Berlin, Germany, 2018-11): Backbone vibrations of hy- Phys. Chem. B 122 (2018) 7375–7384 drated DNA and RNA as noninvasive probes of ultrafast structural dynamics PMC18: B. M. Pilles, B. Maerz, J. Chen, D. B. Bucher, P. Gilch, B. Kohler, W. Zinth, B. P. Fingerhut, and W. J. O. Kornilov, Time-resolved photoelectron spectroscopy Schreier; Decay pathways of thymine revisited; J. Phys. of organic molecules in aqueous solution, DPG Spring Chem. A 122 (2018) 4819–4828 Meeting: (Erlangen, Germany, 2018-03)

E. T. J. Nibbering together with F. Dahms, A. Kundu, M. in press Ekimova, F. Hoffmann, G.Bekçioğlu-Neff, B. P. Finger- hut, D. Sebastiani, E. Pines, and T. Elsaesser; 256th DKP: F. Dahms, A. Kundu, E. Pines, B. P. Fingerhut, ACS National Meeting & Exposition (Boston, MA, USA, E. T. J. Nibbering, and T. Elsaesser; Ultrafast dynamics 2018-08): Ultrafast mid-infrared spectroscopy of hydrat- of hydrated excess protons in CH3CN:H2O mixtures; in ed protons and proton transport in solvent mixtures Ultrafast Phenomena XXI

69 3.2: Solids and Nanostructures: Electrons, Spins, and Phonons

D. Schick, C. von Korff Schmising, S. Sharma, and M. Wörner (project coordinators) and K. Busch, P. Elliot, G. Folpini, A. Ghalgaoui, R. Grunwald, M. Hennecke, P. Jürgens, F. Mahler, A. Mermillod-Blondin, Q. Li, T. Noll, M. Oelschläger, B. Pfau, I. Radu, K. Reimann, V. Shokeen, C. Somma, N. Singh, C. Strüber, J. W. Tomm, P. Varytis, D. Weder, R. Wehner, F. Willems, K. Yao.

1. Overview Quantum dot (QD) emitters and GaN-based structures are investigated in cooperation with F. Yue of the East This project addresses ultrafast and nonlinear phenom- China Normal University in Shanghai. Together with the ena in solids and nanostructures. In highly correlated Leibnitz-Institutes, FBH, Paul-Drude-Institut (PDI) and condensed-matter systems, interaction of electrons, Institut für Kristallzüchtung (IKZ), we investigate AlGaN- phonons, and spins leads to a broad range of novel and InGaN-based superlattices. Here fundamental and unusual phenomena, which are interesting from the questions such as carrier localization as well as opto- point of view of both fundamental research and practical electronic applications are addressed. applications. To gain new insight into fundamental phenomena in this thriving field of research, experiments T4: Magnetism and transient electronic structure are performed with ultrafast time resolution and in a very wide spectral range extending from terahertz (THz) Cooperation partners are various principal investiga- to X-ray frequencies. The work includes studies in the tors within the Collaborative Research Center TRR 227 range of nonperturbative light-matter interactions. “Ultrafast Spin Dynamics” (MBI projects: A02, A04), J. Lüning, Sorbonne Universités, Paris, France, This research is complemented by studies of light-mat- S. Bonetti, Stockholm University, Uppsala University, ter interactions in materials processing with ultrashort Sweden, M. Albrecht, Augsburg University, A. Kalash- optical pulses and by work on optoelectronic devices. nikova and R. Pisarev, IOFFE Institute, St. Petersburg, The project includes five topics. Russia, U. Nowak, Konstanz University, T. Ostler, Shef- field University, UK, A. Tsukamoto, Nihon University, Chiba, Japan, E. K. U. Gross, MPI Halle, M. Schultze MPQ Garching, M. Münzenberg, Greifswald University. 2. Collaborations Projects: BMBF 05K16BCB DynaMaX in cooperation T1: Nonlinear THz and mid-infrared spectroscopy with M. Weinelt, FU Berlin, BMBF 05K16BCA Fem- to-THz-X in cooperation with M. Bargheer, Potsdam Cooperation partners: K. Biermann, Paul-Drude-Institut, University, J. Larsson, Lund University, Sweden, P. Op- Berlin, C. Flytzanis, Ecole Normale Supérieure, Paris, peneer, Uppsala University, Sweden. I. Brener, Y. Yang, J. L. Reno, Sandia National Laborato- ries, Albuquerque, USA, and P. Q. Liu, State University T5: Joint HU-MBI Group on Theoretical Optics of New York at Buffalo, USA. Projects: within the DFG-SPP-1839 “Tailored Disor- T2: Material modification with femtosecond laser der”, project Bu 1107/10-1 “Light-path engineering in pulses disordered waveguiding systems” and Bu 1107/12-2 “Non-Markovian continuous-time quantum random Cooperation partners: E. McGlynn, School of Physics, walks of multiple interacting particles”. Dublin City University, Dublin, Ireland, F. Güell, Univer- sity Barcelona, Spain, S. K. Das and P. Satapathy, KIIT Cooperation partner: W. Pernice, University of Münster, Odisha, India, A. Pfuch, INNOVENT, Jena, Germany, A. Szameit, University of Rostock, N. A. Mortensen, Uni- T. Fennel, University of Rostock, visiting Professor at versity of Southern Denmark, R. de Jesus Leon-Mortiel, MBI. Project: DFG ME4427/1-1 "Fundamental Inves- Universidad Nacional Autonoma de Mexico, and S. Lin- tigations and Micromatching with Few-Cycle Pulses in den, University of Bonn. the Volume of Wide-Bandgap Dielectrics".

T3: Optoelectronic devices 3. Results in 2018 The group works directly on diode lasers in the BMBF project "Spectroscopic analysis of GaN-based single T1: Nonlinear THz and mid-infrared spectroscopy emitters and bars, direct-blue kilowatt diode lasers" (BlauLas) 13N13901, which will be finalized in 2019. Ad- Resonant second-order nonlinear terahertz response of ditional collaborative work on this subject is carried out gallium arsenide on the Adlershof campus together with Jenoptik Diode Lab and the Ferdinand-Braun-Institut (FBH). Analytical The bulk photovoltaic effect is a long-known phenome- work on GaN-based diode lasers is done in cooperation non in materials without inversion symmetry. Absorption with G. Mura from the University of Cagliari, Italy. of light is accompanied by a directed electric current in a homogeneous material. This is in contrast to solar cells,

70 duration which are tunable from λ = 900 nm to λ = 650 nm, are sent onto a (111)-oriented thin layer of bulk GaAs. The corresponding photon energies are at or above the bandgap of GaAs at room temperature, so that the incident light is strongly absorbed. The resulting emission in the THz spectral range is measured with electro-optic sampling, allowing the full characterization of the emitted radiation in amplitude and phase [GRW18].

Electric field The observed THz radiation [Fig. 1 (b),(c)] consists of three components: (i) emission from transverse optical (TO) phonons, (ii) oscillations from coherent heavy- hole–light-hole polarizations, and (iii) the shift current -0.5 0.0 0.5 1.0 1.5 due to the bulk photovoltaic effect. Time [ps] Since GaAs has no inversion symmetry, it’s TO phonons are both Raman and infrared active, allowing their excitation by a Raman process and the emission of THz 1 radiation with the TO phonon frequency at 8 THz. This TO phonon emission is characterized by a rather long lifetime of about 1 ps and a frequency independent of excitation wavelength.

Spectral intensity [arb. u.] 0 0 5 10 15 20 25 Frequency [THz] For photon energies above the bandgap, one excites holes both in the heavy- and the light-hole valence band Fig. 1: and generates a coherent superposition of heavy- and (a) Principle of the experiment: A short pulse in the light-hole states. This intervalence band polarization near-infrared or visible spectral range is sent onto a thin emits THz radiation with a frequency equal to the split- GaAs layer. The electric field of the emitted THz radia- ting between both valence bands, which in turn depends tion is measured as a function of time. (b) An example on the excitation wavelength. of such a THz waveform. It contains oscillations with a period of 0.08 ps corresponding to a frequency of The origin of the shift current emission is illustrated in 12 THz. (c) Spectrum of the THz emission from the opti- Fig. 2 (a) where the unit cell of the GaAs is shown. In the cally excited sample showing the three components. ground state of the crystal represented by the electronic valence band, the valence electrons are concentrated on the bonds between the Ga and the As atoms, Fig. 2 (b). which rely on inhomogeneities (most solar cells consist Upon absorption of near-infrared or visible light, an elec- of p- and n-doped layers). tron is promoted from the valence band to the conduction band. In the new state, the electron charge is shifted Until recently, there has been a controversial debate towards the Ga atoms, Fig. 2 (c). This charge transfer among theoreticians whether the bulk photovoltaic ef- corresponds to a local electric current, the interband or fect is due to intraband or interband motions of elec- shift current, which is fundamentally different from the trons. To study this problem, ultrashort pulses of a 30 fs electron motions in intraband currents.

0.6

0.4

0.2

0.0 Position [0 0 z]

-0.2

0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 Position [x x 0]

Fig. 2: (a) Unit cell of the semiconductor gallium arsenide (GaAs). Chemical bonds (blue) connect every one Ga atom to four neighboring As atoms and vice versa. Valence electron density on the grey plane of (a) in the (b) ground state (the electrons are in the valence band) and in the (c) excited state (the electrons are in the conduction band). Apart from the valence electrons shown, there are tightly bound electrons near the nuclei.

71 Model calculations based on the interband transfer of emission is in fact largely dominated by the transport of electrons in a pseudo-potential band structure reproduce the electrons across the bandgap, a phenomena which the experimental results and show that a real-space has been overlooked up to now. transfer of electrons over the distance on the order of a bond length represents the key mechanism. This pro- Our results extend the understanding of harmonic gen- cess is operative within each unit cell of the crystal, i.e., eration in solids and will enable to gain unprecedented on a sub-nanometer length scale, and causes the rectifi- insights into the fundamental aspects of laser-matter cation of the optical field. Thus, the present experiments interaction in an intensity regime relevant for microma- show unambiguously that the bulk photovoltaic effect is chining applications. For instance, this work provides an due to interband motions of electrons. The effect can original approach to solve the longstanding question of be exploited at even higher frequencies, offering novel the relative importance of electron impact ionization with interesting applications in high-frequency electronics. respect to strong-field ionization in the formation of laser-induced electron plasma.

T2: Material modification with femtosecond laser pulses T3: Optoelectronic devices

Dynamics of excitation and structure formation at semi- Optoelectronic devices and semiconductor structures conductor surfaces are investigated by transient photoluminescence (PL) and micro-Raman spectroscopy. In case of high-power The interaction of intense laser fields with nanostruc- diode lasers this is done in order to identify their funda- tured surfaces was comprehensively discussed in an ar- mental limitations in terms of emission power and reli- ticle for Encyclopedia of Interfacial Chemistry [LSE18]. ability. The devices are provided by industrial partners Original results on enhanced proton generation and within the frame of cooperative projects such as Blau- hybrid mechanisms of the plasmon assisted formation Las together with Osram Opto Semiconductors, Coher- of laser-induced surface structures in silicon were pre- ent-Dilas, and Laserline, funded by the BMBF or within sented. For large area laser structuring, the scanning the frame of bilateral research contracts. In cooperation line focus method was used which was previously de- with FBH the thermal lens of broad area high-power di- veloped at MBI. With femtosecond laser-produced com- ode lasers was investigated [RWK18]. pound nanoripples consisting of titania coated silicon with periods of about 600 nm, photocatalysis was found Analysis of the Catastrophic Optical Damage (COD) in to speed up significantly [SPG]. An enhancement of diode lasers, a relevant sudden degradation mecha- photocatalytic activity in standard dye (methylene blue) nism, is an important part of the work in cooperation with by up to a factor 1.5 was reported. The findings indicate industry [TKL18, TKM18]. GaN-based diode lasers were the practical relevance of the approach. intentionally damaged with single sub-µs current pulses. COD becomes evident as surface modification at the Laser-induced plasma formation in solid dielectrics aperture of the devices, where the 450-nm laser emission leaves the waveguide of a device. Subsequently, Understanding the formation of a laser-induced electron we analyze the related damage pattern inside the de- plasma upon irradiation in wide bandgap solid dielec- vice. Knowledge about the operating conditions, degra- trics is crucial to develop and optimize controlled laser material micro- and nanoprocessing applications.

In order to gain insights into the extremely fast processes governing optically induced plasma formation, a time-re- 0.0 solved detection of low-order harmonics relying on a pump-probe scheme was implemented. We confirmed that strong-field ionization (SFI) triggers the emission of harmonics of the pump laser beam, as already observed in gases. The harmonics appear at the frequencies 0.5 Time [ns] Time 2nω0 + ω1 where ω0 and ω1 are the frequencies of the pump and the probe beams, respectively. PL & Absorbance [norm.] & PL In the past, SFI-related harmonics have not been only observed in gases. Their existence has also been reported 1.0 1..7 1.6 1.5 in solids, but up to the order n = 1 only. Our experimental Wavelength [µm] results show the appearance of a harmonic spectrum up to the spectral limit of the detector, corresponding to the order n = 4 in our experimental conditions. Fig. 3: Photoluminescence and the absorption of PbSe:Glass, Up to the present point, these harmonics were associat- whereby the maxima are Stokes-shifted. In case of ed to the stepwise subcycle modulations of the plasma pulsed excitation, there is a strong emission from excited density in the conduction band. In the frame of a col- states at much shorter wavelengths and a very fast re- laboration with T. Fennel (visiting professor at the MBI), combination kinetics on the time scale of 25-40 ps. we found out that the mechanism of low-order harmonic

72 dation time and the energy introduced into the defect quenching and subsequent recovery of magnetic order, allows estimates of the temperature during the process, the generation of spin currents, as well as deterministic ~1000°C, and defect propagation velocity, 110 µm/µs. Fur- switching of magnetization. In magnetic solids the cou- ther analysis of this data allows for conclusions regarding pling of the spin and orbital momenta to the electronic the mechanisms that govern defect creation at the surface charge distribution and to lattice degrees of freedom and defect propagation inside the device [TKM18]. are extremely complex. Hence, different experimental approaches in close collaboration with theory have to Transient PL of PbSe QDs in a glass matrix (PbSe:- be applied in order to gain a deeper understanding and Glass) is investigated at high excitation levels [HWY18]. thus enable the direct control of the involved microscop- Up to 470 meV blue-shifted emissions are observed, ic physical processes. which are assigned to excited-state emission populated by carrier accumulation. Rapid photoluminescence de- We employ different pump-probe techniques ranging cays of 25–40 ps are observed; see Fig. 3. Together with from THz to soft X-rays, including visible and XUV radia- a threshold-like dependence on excitation, even at room tion to excite and monitor the ultrafast charge, spin, and temperature, this component is tentatively attributed to lattice dynamics in functional magnetic systems. We amplified spontaneous emission. have build-up a THz setup delivering intense single-cycle pulses with electric field strengths above 1 MV/cm Heavily n-doped GaN/Al0.18Ga0.82N short-period super- and routinely utilize time-resolved optical MOKE/Fara- lattices (SL) with and without SiN protection layers are day spectroscopy and microscopy. Our higher-harmon- studied in spectrally and temporally resolved PL exper- ic-driven spectroscopy setup employs X-ray magnetic iments [MTR18]. The room-temperature PL from a pro- circular dichroism (XMCD) in the XUV range and works tected sample displays a non-exponential decay with an in close collaboration with resonant small angle scat- initial decay time of 150 ps for low excitation levels and tering and coherent imaging experiments within Proj- an exponential decay with a time constant of ~300 ps ect 3.3. Our in-house approaches are complemented for higher excitation. The PL decays are governed by by experiments at large scale facilities such as synchro- non-radiative carrier relaxation into deep defect states trons, including femto-slicing, as well as free electron which are partially saturated at high excitation densities. lasers (FELs) in the THz, XUV, and soft X-ray spectral PL measurements at low sample temperature reveal a range. Theoretically, we apply time-dependent densi- marked influence of carrier cooling on the PL kinetics ty functional theory (TDDFT) and strongly benefit from in a time range up to 50 ps and a significant radiative in-house sample preparation capabilities within Project decay component. SiN coatings are shown to provide 4.3 in order to optimize the sample geometry on the na- long-term stabilization of surface morphology while in- noscale both for experiment and theory. creasing non-radiative carrier relaxation rates. Phonon-driven ultrafast demagnetization of an insulating ferrimagnet T4: Magnetism and transient electronic structure Manipulating and controlling the spin degree of freedom Ultrashort light pulses can induce and probe dynamics in magnetically ordered materials require a fundamen- in functional magnetic systems on various length, time, tal understanding of the way spins interact with the sur- and energy scales. These dynamics include sub-ps rounding crystal lattice. Within a collaborative effort we

Fig. 4: (Left) Intense THz pump pulses resonantly excite a transversal optical phonon mode that modulates the Fe-O exchange interaction at tetrahedral sites of YIG (red broken arrow). (Right) Absorption [arb. units] 0 The upper panel shows 20 25 30 35 the phonon absorption Frequency [THz] spectrum of YIG and the schematic illustration of the on- and off-resonant THz 0 excitation at 20 THz and 35 THz, respectively; the subsequent demagnetiza- -1 tion dynamics as measured with magneto-optical Faraday effect in the visible

Transient faraday rotation [%] Transient -1 0 1 2 3 4 5 6 7 spectral range is shown in Pump-probe delay [ps] the lower panel.

73 have recently revealed the fl ow of energy and angular momentum between lattice and spins in the insulating model ferrimagnet yttrium iron garnet (YIG) following 20 resonant phonon excitation [MRM18]. 0

A(t) [a. u.] -20 Such a selective and resonant lattice excitation, which 3 leaves the electronic sub-system unperturbed, drives 2

an ultrafast demagnetization process that evolves on a ] B surprisingly fast time scale of few picoseconds (Fig. 4). 1 In particular, by exciting the Fe-O asymmetric stretch vi- 0 M(t) [µ bration in YIG using intense mid-IR pulses, we are able -1 to quench the magnetization of the sample with a time constant of ~1 ps, through a very effi cient phonon-mod- -2 0 10 20 30 40 50 60 ulation of the Fe-O exchange interaction. Subsequently, Time [fs] the global equilibration of spin angular momentum proceeds much slower on a 100 ns time scale. Our results imply that spin transport phenomena and effi cient spin Fig. 5: control by phonons can be extended well into the tera- (Top) The electric fi eld of the pump laser pulse (Bottom) hertz frequency range. Time evolution of the layer resolved local magnetic moments in a Co/Mn multilayer. Magneto-optical functions at the 3p resonances of Fe, Co, and Ni density functional theory as implemented in the Elk In recent years the use of XMCD in the XUV regime code [elk.sourceforge.org]. In the ground state this sys- has strongly increased due to the growing availability tem has a magnetic confi guration in which the Mn layer of laboratory based HHG sources. However, all previ- at the Co interface is AFM-coupled to all other layers. ous calculations of M-edge spectra even for the most Under the infl uence of a femtosecond laser pulse the common 3d transition metals (Fe, Co, and Ni) rely on spin dynamics differ dramatically for the different con- ad-hoc Gaussian broadening, energy shifts, and ampli- stituents of the multilayer: while the Co layers show tude scaling to bring theoretical results close to exper- very little change in spin polarization, the two Mn layers iments. In our work [WSK] we present theoretical and demagnetize strongly under the infl uence of the laser experimental data on the magneto-optical contributions pulse. Most interestingly, slightly before the peak of the to the complex refractive index in the XUV range cover- laser pulse, the interface AFM-coupled Mn layer switching M-edges of Fe, Co, and Ni. Comparing the spectra es the direction of its moment, thus changing the mag- from density functional theory with magnetic circular di- netic order of the multi-layer from AFM to FM. Based on chroism measurements we fi nd that many-body correc- these fi ndings ultrafast control over the spin structure is tions and local fi eld effects are of crucial importance for possible and governed purely by electronic processes. accurate description of the spectra. Our results will have direct consequences not just for static but also dynamic XUV spectroscopy studies, e.g. performed in the fi elds T5: Joint HU-MBI group on theoretical optics of femtomagnetism and spintronics. Desgin and realization of random spectrometers Optical inter-site spin transfer In an integrated random spectrometer, the input signal The type of magnetic coupling between the constituent is mixed-up via multiple scattering in a disordered region atoms of a solid, i.e., ferromagnetic, anti-ferromagnetic, or non-collinear, is one of the most fundamental properties of any magnetic material. This magnetic order is governed by the exchange interaction, which is associated (from the energy-time uncertainty relation) with a characteristic time scale at which spin-fl ip scattering processes and changes the intrinsic magnetic structure 20µ 20µ m occur (~40-400 fs for transition metal systems). Here, m we demonstrate that spin transfer driven by inter-site 100µ spin-selective charge transfer, OISTR, [AHH, CBE, m SGO], is one of the key mechanisms that underpins spin manipulation at sub-exchange time scales. This charge fl ow is induced by optical excitations and represents the Fig. 6: fastest possible spin response of an electronic system Designed integrated random scattering area (right panel) to a laser pulse, which is also highly sensitive to the in- with alphorn fi ber-to-chip coupler in- and out-couplers tensity and time structure of the driving laser fi eld. (left panel) combined into a silicon-nitride based random spectrometer with one in- and thirteen output ports (only Figure 5 shows results for a multi-layer system consist- four couplers are shown). Courtesy of W. Hartmann ing of two mono-layers (ML) of Mn and four ML of Co, (University of Münster). on a Cu(001) substrate obtained using time-dependent

74 Fig. 7: [dB] (a) (d) 1.0 -10 2 Simulated perfor- 0.8 4 mance (TE polariza- 6 0.6 tion) of the full random 8 C [ Δλ ] 0.4 10 spectrometer device 0.2 12 depicted in Fig. 6 for 0.0

Detector channel 1500 1520 1540 1560 1580 1600 0 1 2 3 4 5 6 7 8 three different op- Wavelength [nm] Δ λ [nm] (b) (e) 1.0 eration wavelength 2 ranges (left column) 4 0.8 6 0.6 and resulting spectral

8 C [ Δλ ] 0.4 correlation functions 10 0.2 with the corresponding 12 Transmission 0.0 indicated spectral res- Detector channel 1000 1020 1040 1060 1080 1100 0 1 2 3 4 5 6 7 8 olution (right column). Wavelength [nm] Δ λ [nm] (c) (f) 1.0 2 0.8 4 6 0.6

8 C [ Δλ ] 0.4 10 0.2 12 0.0

Detector channel 700 720 740 760 780 800 0 1 2 3 4 5 6 7 8 -30 Wavelength [nm] Δ λ [nm]

and the resulting speckle pattern is read-out through a fi lled with 9 % (by area) pores of diameter 250 nm each, number of waveguides. For broadband and robust op- suggesting resolutions (half-width half-max) as indicat- eration, the area with the random scattering region has ed in Fig. 7 for three different frequency ranges of oper- to be large enough so that the system is diffusive (as ation. Clearly, the effi cient practical performance of the otherwise, the position and shape etc. of every scatterer device also requires effi cient couplers from fi bers to the would be important). On the other hand, this area should on-chip waveguides. To this end, a completely novel ul- not be too large because eventually the out-of-plane tra-broadband fi ber-to-chip coupler, called the Alphorn losses would quickly reduce the signal strengths to un- coupler (written in polymer via direct laser writing) has acceptably low values (detector limitations). been developed.

In Figure 8, it is demonstrated that we can really reconstruct input signals and separate wavelengths with res- 1.0 olutions fairly close to the design specs. The red dashed line is the center frequency of the (known) input pulse(s) 0.8 and the blue lines are the signals reconstructed from the measured data. 0.6

0.4 Normalized intensity 0.2 Own Publications 2018 ff (for full titles and list of authors see appendix 1) 0.0 1570 1580 1590 1600 1610 BSG18a: J. Bonse et al.; Appl. Phys. A 124 (2018) 1-6 Wavelength [nm] DSG18: J. K. Dewhurst et al.; Phys. Rev. Appl. 10 Fig. 8: (2018) 044065/1-8 Reconstructed signal (blue) from known two-color input (center frequencies indicated by the red-dashed line). EMB18: B. Erk, et al.; J. Synchrot. Radiat. 25 (2018) Compare with Fig. 7, top row, for the theoretically expect- 1529-1540 ed resolution. Courtesy of P. Varytis (MBI). GDK18: A. Ghalgaoui, et al.; J. Phys. Chem. C; https:// dx.doi.org//10.1021/acs.jpcc.8b07034 (2018) Thus, design is important and through a combination of multiple-scattering theory (which gives mean free GHW18: A. Ghalgaoui, et al.; J. Phys. Chem. Lett. 9 paths etc.) and direct numerical simulation (which gives (2018) 5202–5206 in- and out-coupling losses, out-of-plane losses etc.) we have designed the silicon-nitride based system GRW18: A. Ghalgaoui, et al.; Phys. Rev. Lett. 121 shown in Fig. 6 [VHH18]. The semi-circular area (radius (2018) 266602/1-6 30 µm) represents the random scattering area and is

75 HVB18a: W. Hartmann, et al.; Waveguide-integrated FRW: G. Folpini et al.; in Ultrafast Phenomena XXI single photon spectrometer based on tailored disorder; SPIE Proc. 10688 (2018) 106880W WSRa: M. Woerner et al.; in Ultrafast Phenomena XXI

HVB18b: D.-N. Huynh et al.; SPIE Proc. 10688 (2018) 106880V/1-8 submitted

HWY18: J. Hong et al.; Phys. Status Solidi-Rapid Res. AHH: M. Aeschlimann et al.; Science Lett. 12 (2018) 1800012/1-6 ASM: M. Anikeeva et al.; Phys. Rev. B KWD18: S. Kovalev et al.; J. Phys. D 51 (2018) 114007/1-8 CBE: J. Chen et al.; Phys. Rev. Lett.

LSE18: A. Lübcke et al.; Encyclopedia of Interfacial KWH: R. Kernke et al.; Opt. Lett. Chemistry: Surface Science and Electrochemistry / Ref- erence Module in Chemistry, Molecular Sciences and MTR: F. Mahler et al.; J. Appl. Phys. Chemical Engineering, K. Wandelt ed. (Elsevier, Kidling- ton, Oxford, UK, 2018) SGO: F. Siegrist et al.; Nat. Phys.

MRM18: S. F. Mährlein et al.; Sci. Adv. 4 (2018) 5164/1-7 SPG: P. Satapathy et al., Catalysts

MKS18: M. Moeferdt et al.; Phys. Rev. B 97 (2018) WES: C.-Y. Wang et al.; J. Phys.-Condens. Mat. 075431/1-10 WFG: D. Weckbecker et al.; Phys. Rev. Lett. MTR18: F. Mahler et al.; Phys. Rev. B (R) 97 (2018) 161303/1-5 WGR: D. Weckbecker et al.; Nano Lett.

OBI18: M. Oelschläger et al.; Phys. Rev. A 97 (2018) WSK: F. Willems et al.; Phys. Rev. Lett. 062507/1-13 WSRb: M. Woerner et al.; Phys. Rev. Lett. PWF18: M. Peter et al.; Appl. Phys. B 124 (2018) 83/1-6

PZK18: D. Polley et al.; J. Phys. B 51 (2018) 224001/1-9 Invited Talks at International Conferences RWK18: J. Rieprich et al.; J. Appl. Phys. 123 (2018) (for full titles see appendix 2) 125703/1-11

TGW18: C. Tserkezis et al.; Phys. Rev. B 98 (2018) S. Eisebitt; 15th Epioptics School and 3rd Silicene 155439/1-8 Workshop (Erice, Italy, 2018-07)

TKL18: J. W. Tomm et al.; SPIE Proc. 10553 (2018) T. Elsaesser; EOS Topical Meeting on Terahertz Sci- 1055308/1-7 ence & Technology 2018 (Berlin, Germany, 2018-05)

TKM18: J. W. Tomm et al.; J. Electron. Mater. 47 (2018) T. Elsaesser; Ultrafast Phenomena XXI (Hamburg, Ger- 4959 many, 2018-07)

TKS18: E. Travkin et al.; Phys. Rev. B 97 (2018) T. Elsaesser; Primary Processes of Matter (Chinese 195133/1-5 Academy of Sciences, Bejiing, China, 2018-11)

VHH18: P. Varytis et al.; Opt. Lett. 43 (2018) 3180/1-4 T. Elsaesser; International Symposium on Ultrafast Sci- ence: From the infrared to the X-rays (Lausanne, Swit- WRE18: M. Woerner et al.; in Encyclopedia of Modern zerland, 2018-11) Optics, 2nd ed., vol. 2, B. D. Guenther, and D. G. Steel eds. (Elsevier, 2018) 197-206 A. Mermillod-Blondin; Progress in Ultrafast Laser Modi- fications of Materials (Telluride, USA, 2018-06) WBM18: C. Wolff et al.; Phys. Rev. B 97 (2018) 104203/1-14 K. Reimann; 16th International Conference on Phonon Scattering in Condensed Matter (Phonons 2018) (Nan- jing, China, 2018-05) in press S. Sharma; SPICE Workshop 2018: Ultrafast Spin- EFS: T. Elsaesser et al.; in Ultrafast Phenomena XXI tronics: from Fundamentals to Technology (Johannes Gutenberg Universität Mainz, 2018-10) ERW: T. Elsaesser et al.; Morgan & Claypool Publish- ers, San Rafael, CA, USA

76 J. W. Tomm; SPIE Photonics West 2018 (San Francis- co, CA, USA, 2018-01)

J. W. Tomm; 2018 MRS Spring Meeting & Exhibit (Phoe- nix, AZ, USA, 2018-04)

J. W. Tomm; 26th International Semiconductor Laser Conference, ISLC2018 (Santa Fe, NM, USA, 2018-09)

J. W. Tomm; The 10th International Conference on Pho- tonics and Applications (Ha Long City, Vietnam, 2018- 11)

F. Willems; Transregio 227 Retreat (Halle, MLU, Ger- many, 2018-06)

F. Willems; SPICE Workshop 2018: Ultrafast Spin- tronics: from Fundamentals to Technology (Johannes Gutenberg Universität Mainz, Germany, 2018-10)

M. Woerner; Discussion Workshop “Light field induced dynamics in low dimensional systems” (Universität Duis- burg-Essen, Germany, 2018-04)

77 3.3: Transient Structures and Imaging with X-rays

M. Woerner, B. Pfau (project coordinators) and D. Engel, C. Hauf, P. Hessing, M. Holtz, A. Jonas, C. von Korff Schmising, J. Lebendig-Kuhla, M. Schneider, H. Stiel, J. Tümmler, J. Weißhaupt, K. Witte

1. Overview 3. Results in 2018

The aim of project is the development and application T1: Nanoscale imaging and spectroscopy with soft of XUV and X-ray sources for structure analysis and im- X-rays aging with high spatial and temporal resolution down to atomic length scales. The current applications focus on Results from the use of x-ray holography in conjunction ultrafast optically induced structural dynamics as, e.g., with magnetic contrast provided by x-ray magnetic cir- strain waves, phase transitions, and transient charge cular dichroism (XMCD) in the study of magnetic skyr- densities investigated with time-resolved X-ray diffrac- mions is featured in a highlight of this annual report and tion and absorption spectroscopy. A second focus is on discussed in detail in Ref. [CMB18]. imaging the spin structure in nanometer-scale magnetic materials in equilibrium and after excitation. The evalu- A setup for resonant x-ray holography for use at the P04 ation of new imaging techniques utilizing the light from soft x-ray beamline at PETRA III (DESY, Hamburg) has coherent, highly brilliant soft-x-ray sources as well as the been designed and components have been procured in user operation of a laboratory based x-ray microscope 2018 for installation at DESY in 2019. for the water window region are subjects of collaboration with partners from academia and industry. Nanometer phase coexistence during insulator-metal phase transformation

Vanadium dioxide (VO2) is insulating at low tempera- 2. Topics and collaborations tures and metallic above about 65°C. The change in the electronic structure is accompanied by a change of the T1: Nanoscale imaging and spectroscopy with soft crystal structure from a monoclinic (M1) structure to a X-rays rutile (R) structure, with a minute change of atomic positions. The driving forces for this phase transition have The topic is centered around imaging and spectrosco- been a matter of long standing debate, specifically the py of nanoscale objects with XUV and soft-x-ray radi- role of electronic correlation in thin VO2 films, where it ation produced at synchrotron-radiation sources and had been reported that the material turns metallic at free-electron lasers as well as by laser-driven laboratory slightly lower temperatures even before the atoms rear- sources. Part of the research in this topic is performed range to the R-structure. in the framework of the Berlin Laboratory for Innovative X-ray Technologies (BLiX) which is jointly operated by We have investigated this phase transition in thin VO2 the TU Berlin and MBI (cf. Project 4.2). Prroject 3.3 also films using x-ray spectro-holography, shedding light on hosts activities where a x-ray split-and-delay line for in- the role of nanoscale inhomogeneity in the phase tran- stallation at the Materials Imaging and Dynamics (MID) sition mechanism [VGM18]. We observe that defects instrument at the European XFEL facility in Hamburg is in the VO2 film can locally change the pathway of the developed. phase transition. The picture emerging when scanning the temperature through the phase transition as shown Collaboration partners: F. Büttner, G. S. D. Beach (MIT, in Fig. 1 is the following: USA), E. Jal, B. Vodungbo, J. Lüning (Sorbonne Uni- versités, UPMC Univ Paris, France), A. Madsen, L. With increasing temperature, growth of metallic regions Wei (European XFEL, Germany), G. Schütz (MPI-IS, in R-structure starts from nanoscale defects. Strain in Stuttgart, Germany), S. Wall (ICFO, Spain), HZB (Ber- the neighborhood of the defects reduces the energy lin, Germany), Fraunhofer ILT (Aachen, Germany), op- barrier for the M1 to R transition. In turn, the volume tiX fab GmbH (Jena, Germany), GIST (Gwangju, Rep. mismatch between these two phases locally generates Korea), KTH (Stockholm, Sweden), FSU Jena (Jena, a new strain field, triggering the growth of domains in Germany), greateyes GmbH (Berlin, Germany). yet another, different monoclinic phase M2 in adjacent regions. This effect leads to a coexistence of different T2: Femtosecond X-ray diffraction and absorption phases of the material on the nanometer length scale, as seen, e.g., as a stripe pattern at 335 K (62°C) in Fig. 1 Investigation of phase transitions and structural dynam- At higher temperature, these still insulating regions of ics in solids, in close collaboration with project 3.2. M2 phase will ultimately also transform into the metallic R phase – just like some of the M1 phase patches will do directly. The pathway for the insulator to metal phase transition is thus not homogeneous throughout the thin VO2 film, but varies spatially. Our results show

78 no evidence for reduced electronic correlations or a new 7 nm Ta, 50 nm Gd, 50 nm Tb and 50 nm Dy on a Si3N4 monoclinic yet metallic phase below the phase transition substrate (Fig. 2). The M-edges of the three lanthanides temperature, as has been discussed in the past. The are clearly resolved, matching literature data. A design results highlight the importance of combining spatial and to use the source for time-resolved resonant diffraction spectroscopic resolution and will serve as the basis to experiments has been developed for implementation in study the transient behavior during laser-driven phase 2019. transitions in materials with electronic correlation.

0.35 300K 330 K 332 K

0.30

0.25

333K 334 K 335 K µd 0.20

0.15 337K 338 K 339 K 0.10 1150 1200 1250 1300 1350 Photon energy [eV]

340 K 346 K 360 K Fig. 2: M-edge NEXAFS spectrum of a sandwich structure consisting of 7 nm Ta, 50 nm Gd, 50 nm Tb and 50 nm

500 nm Dy on a Si3N4 substrate obtained with the LPP source setup.

Fig. 1: Images of the phase separation occurring when heat- X-ray split-and-delay unit for use at the European XFEL

ing a 75 nm thin VO2 film. The images were acquired via x-ray spectro-holography and are displayed in false Split-and-delay optics for hard x-rays at a free-electron color to indicate the different regions: red = defect x-ray laser allow for x-ray-pump–x-ray-probe experi- region, black = insulating M1 phase, blue = insulating ments, sequential imaging and the implementation of a M2 phase, green = metallic R phase. Note that some sequential form of x-ray photon correlation spectrosco- sample regions transition directly from M1 to R (e.g. at py (XPCS). For installation at the Materials Imaging and cross marker) while others transition via the intermedi- Dynamics (MID) Instrument at the European XFEL, we ate M2 phase (e.g. at diamond marker). are developing such a device within a BMBF project, based on Bragg diffraction from Si(220) crystals, allowing to cover a delay range from -10 ps to 800 ps. The X-ray absorption spectroscopy using a high-repeti- high demands of the setup in terms of position accuracy tion-rate laser-produced plasma source of the optical elements together with requirements for vacuum and particle cleanliness required the develop- We have set up a laser-produced plasma (LPP) source ment of tailored precision mechanics and x-ray beam for pump-probe experiments with a few-picosecond diagnostics. After the final design and performance sim- temporal resolution, filling the temporal resolution gap ulations [LFN18], the main custom made parts of the de- between synchrotron-radiation pulses generated from vice have been delivered at the end of 2018. The x-ray storage rings on one hand and high-harmonic genera- split-and-delay device will now be assembled and com- tion sources and free-electron lasers on the other hand. missioned; installation at XFEL beamline is foreseen for In addition, the system serves as an in-house source of 2019. soft x-rays to test optical elements and concepts in this spectral range. T2: Femtosecond X-ray diffraction and absorption The source is based on a high-repetition-rate chirped- pulse amplification (CPA) laser system (1.5 ps, 160 mJ, The analysis of the transient electron density ρ(r,t) in 100 Hz) relying on thin-disk technology developed at crystalline materials allows to resolve atomic motion or MBI as a pump source hitting a metal target with an relocation of electronic charge on atomic time and length intensity of 1016 W/cm2. The spectral range from 100– scales. ρ(r,t) is typically obtained from femtosecond 2000 eV is covered with W and Cu targets. A pump- x-ray diffraction employing an optical-pump/x-ray-probe probe setup using a spectrometer with reflection zone setup. In our experiments, the necessary femtosecond plates (RZP) as dispersive elements has been set up for hard x-ray pulses have up to now been generated by a near-edge x-ray absorption fine structure (NEXAFS) in- table-top source driven by an amplified Ti:sapphire laser vestigations. In order to optimize the performance of the system with a center wavelength of 800 nm. Based on setup, first overview absorption spectra of thin magnetic such a source we have recently investigated the elec- films have been recorded from a sample composed of tronic dynamics during the vibration of a hybrid-mode

79 in molecular aspirin and the polarization dynamics in the promising results from earlier experimental and the- prototype ferroelectrics by employing x-ray powder dif- oretical proof of concept studies, a mid-Infrared (mid-IR) fraction [HHH, HWE18, HHH18]. The reconstruction of laser system now serves for driving a new x-ray source the transient microscopic and macroscopic polarization specifically designed for this purpose. The proof-of-con- changes P(t) in ferroelectric (NH4)2SO4 and paraelectric cept studies have shown that the characteristic Kα pho- KH2PO4 are discussed in one of the highlights of this ton flux emitted by the laser-driven metal target scales annual report and in detail in Ref. [HWE18] quadratically with the wavelength of the laser radiation. To exploit this potential, an OPCPA system with a centre wavelength of 5 µm and world-record parameters of the sub-100 fs pulses which was recently developed in 400 project 2.2, is now implemented as the driving laser. The demonstrated pulse parameters, i.e., a repetition rate of 1 kHz, a pulse duration of 80 fs, and a pulse energy higher than 3 mJ, are comparable to conventional amplified Ti:sapphire systems. The new x-ray source is expected to be at least one order of magnitude brighter than the current setup.

First light of the new femtosecond hard x-ray source was achieved in 2018, still using 5 µm driver pulses with a sub-optimal temporal compression. To assess the to- 200 tal number of Cu-Kα photons emitted from the Cu tape target in the full solid angle, an energy dispersive detector was used. The resulting spectrum clearly reveals

X-ray intensity [counts] the characteristic Kα lines of copper as shown in Fig. 3. 7 From these data, a total flux of up to 4 x 10 Cu-Kα photons per pulse in the full solid angle is retrieved, a number comparable to optimized sources driven by Ti:sapphire laser systems. The successful commissioning of the entire setup is expected for Spring 2019.

0 8 16 24 32 Photon energy [keV] Own Publications 2018 ff (for full titles and list of authors see appendix 1) Fig. 3: Time [ps] Spectum of the x-ray photon flux generated by a fem- CMB18: L. Caretta et al.; Nat. Nanotech. 13 (2017) tosecond hard x-ray source which is driven by a 5 µm 1154–1160 OPCPA system. The detector is situated 1.8 m away from the source and has an active area of 9 mm2, DBG18: A. Dehlinger et al., Microsc. Microanal. 24 ~2×10-7 of the full solid angle. To avoid multi-photon (2018) 248–249 events, the emitted x-rays were additionally attenuated by inserting thin Cu-foils in the beam path. In the inset, HHH18: C. Hauf et al.; Struct. Dyn. 5 (2018) 024501/1– the generated flux (dashed magenta line) is compared 11 to earlier experimental and theoretical proof of concept studies employing 800 nm/3900 nm (blue/red lines and HWE18: C. Hauf et al.; Phys. Rev. B 98 (2018) symbols respectively) pulses at different levels of peak 054306/1–12 intensity. LFN18: W. Lu et al.; Rev. Sci. Instrum. 89 (2018) 063121/1–9 Novel femtosecond X-ray source SBD18: H. Stiel et al.; X-Ray Lasers 2016, Proceedings The changes of diffracted intensity ∆I/I observed in of the 15th International Conference on X-Ray Lasers our femtosecond x-ray diffraction experiments [HHH, (2018) 265–272 HWE18, HHH18] were on the order of ~1 %. To reliably determine even smaller ∆I/I, or to conduct experiments SGP18: M. Schneider et al.; Nat. Commun. 9 (2018) in a much faster fashion, significantly brighter x-ray 214/16 sources are required. However, the x-ray flux generated in laboratory based sources driven by amplified Ti:sap- VGM18: L. Vidas et al.; Nano Lett. 18 (2018) 3449–3453 phire laser systems is limited by the characteristic output parameters of the driving laser. WMS18: K. Witte et al.; J. Phys. Chem. B 122 (2018) 1846−1851 In 2018, we have therefore begun to implement a new generation of laser driven hard x-ray sources. Following

80 ZGJ18: M. Zürich et al.; X-Ray Lasers 2016, Proceed- B. Pfau; SPIE Optics and Photonics 2018 (San Diego, ings of the 15th International Conference on X-Ray La- USA, 2018-08) sers (2018) 231–241 H. Stiel; 16th ICXRL, International Conference on X-ray Lasers (Prague, Czech Republic, 2018-10) in press M. Woerner; Discussion Workshop “Light field induced EFS: T. Elsaesser et al.; Soft-mode driven dynamics in dynamics in low dimensional systems” (Universität ferroelectrics – new insight from ultrafast terahertz and Duisburg-Essen, Germany, 2018-04) x-ray experiments; in Ultrafast Phenomena XXI

HHH: C. Hauf et al.; Phonon driven charge dynamics in polycrystalline acetylsalicylic acid mapped by ultrafast x-ray diffraction; Struct. Dyn

Submitted

EWo: T. Elsaesser and M. Woerner; Femtosecond x-ray diffraction: Nuclear motions and charge dynamics; in Dynamic Structural Science: Monitoring Chemical and Biological Processes Across Time Domains (Wiley Pub- lishing)

Invited Talks at International Conferences (for full titles see appendix 2)

S. Eisebitt; European XFEL SASE2 Workshop (Schenefeld, Germany, 2018-01)

S. Eisebitt; DPG-Frühjahrstagung der Sektion Konden- sierte Materie gemeinsam mit der EPS (Berlin, Germa- ny, 2018-03)

S. Eisebitt; Synchrotron Radiation Instrumentation, SRI 2018 (Taipei, Taiwan, 2018-06)

S. Eisebitt; Science@FELs 2018 (Stockholm, Sweden, 2018-06)

S. Eisebitt; Bad Honnef Physics School on Physics with Free Electron Lasers (Bad Honnef, Germany, 2018-09)

T. Elsaesser; Int. School of Crystallography: Quantum Crystallography (Erice, Italy, 2018-06)

T. Elsaesser; Ultrafast Phenomena XXI (Hamburg, Ger- many, 2018-07)

T. Elsaesser; Primary Processes of Matter (Chinese Academy of Sciences, Bejiing, China, 2018-11)

T. Elsaesser; Int. Symposium on Ultrafast Science: From the infrared to the X-rays (Lausanne, Switzerland, 2018-11)

T. Noll; 12. Tagung Feinwerktechnische Konstruktion (Dresden, Germany, 2018-09)

B. Pfau; DESY Photon Science Users’ Meeting (Ham- burg, Germany, 2018-01)

81 4.1: Implementation of Lasers and Measuring Techniques

I. Will, N. Zhavoronkov (project coordinators) and U. Bengs, F. Furch, C. Kleine, G. Klemz, M. Kretschmar, L. Lochner, T. Noll, M. Osolodkov, J. Tümmler, T. Nagy, T. Witting

1. Overview 3. Results in 2018

The general goal of this project is the development of T1: Lasers for particle accelerators lasers and optical measurement systems tailored to applications specific to the MBI or laboratories of collabo- This topic deals with the development and systematic ration partners. improvement of photocathode lasers for linear accelerators (linacs) of FELs, as well as with other lasers used An important part of the project is the development and at particle accelerators and storage rings. Photocathode implementation of systems generating sub-10 fs pulses lasers are needed to drive the photo injectors, where the by means of Optical Parametric Chirped Pulse Amplifi- electron bunches are generated prior to the subsequent cation (OPCPA), which increased in significance during acceleration. Thus the parameters of the photocathode the last years. The OPCPA systems are described in laser, in particular its wavelength, synchronization accu- topics 2 and 3 of this project. racy, pulse shape, and stability, have a substantial influence on the performance and stable operation of the linacs and FELs.

2. Topics and collaborations At present, several photocathode lasers developed at the MBI are in operation at DESY, both for the European The project is organized in the following topics: XFEL as well as for FLASH and PITZ, at HZB and at the superconducting RF gun at HZDR. In 2017, we have T1: Lasers for particle accelerators ensured operation of the lasers at DESY and at HZDR (Rossendorf). In addition, we have delivered critical com- This topic deals with the development and implemen- ponents to allow for long-term availability of these lasers. tation of lasers that are either required directly for the operation of particle accelerators, or that are used for We have further proceeded in the development of the experiments at accelerators or storage rings-driven laser for bERLinPro, which has already been described x-ray sources at large scale facilites. In particular, the in detail in the previous Annual Report for 2017. topic contributes to the development of Free Electron Lasers (FELs) by providing highly specialized photo in- The main work in 2018 focused on the development of a jector drive lasers. This work is carried out in coopera- laser to enable pump-probe experiments at the MAXY- tion with DESY, the Helmholtz-Zentrum Dresden-Ros- MUS scanning transmission x-ray microscope (STXM), sendorf (HZDR), and the Helmholtz-Zentrum Berlin für which is operated by the Max Planck Institute for Intel- Materialien und Energie (HZB). ligent Systems, Department Modern Magnetic Systems (Prof. G. Schütz), at BESSY II. T2: Development of a Terawatt OPCPA system This laser will be used in joint experiments on the ma- A high-power OPCPA system that is pumped by a nipulation of magnetization with light pulses on a pico- high-power thin-disk laser is being developed in the second timescale. The laser system will provide optical framework of this topic. This project aims to reach a excitation within the STXM with pulses of several pico- pulse energy in excess of 30 mJ from the OPCPA with a second duration delivered to the sample. This develop- pulse duration of less than 10 fs. The system runs at a ment is the basis for a new project in the competitive repetition rate of 100 Hz. Leibniz-SAW procedure, starting in 2019.

T3: High repetition rate OPCPA Figure 1 shows a scheme of the laser, which combines a diode-pumped Yb:KGW oscillator with a two stage fiber The development of high repetition-rate non-collinear amplifier. OPCPA systems (repetition rate ≥ 100 kHz) is the goal of this topic. The OPCPAs are pumped by fiber lasers The oscillator contains a high-precision linear stage to and by a high-power thin-disk amplifier. allow varying the resonator length by more than 10 cm without stopping the pulse train. Fine tuning of the resonator length with nanometer precision is accom- plished by a combination of two piezos with appropriate synchronization electronics. These components are required to work with the asynchronous pump-probe scheme employed at MAXYMUS. This scheme allows for a controlled detuning of the pump and probe fre-

82 Fig. 1: Simplified scheme of the laser developed for the MAXYMUS scanning transmission x-ray microscope, which is operated at the BESSY II storage ring by the Max Planck Institute for Intelligent Systems.

pulse pulse compressor compressor Fig. 2: outsideoutside the the vacuum vacuum chamber chamber Layout of the pulse compres- fiber sor, as well as a fiber in air 0.5 m long 7 m long fiber-based system for deliver- remotely ing and focusing controlled the laser pulse fiber coupler onto the target in in the vacuum Laser chamber pulses the MAXYMUS vacuum microscope. flange Fiber in vacuum ~ 0.5 m

X-rays

from BESSY undulator focusing system in the vacuum chamber

quencies together with multi-channel acquisition for ef- This development will open the instrument for new re- ficient acquisition of data as a function of pump-probe search topics such as optically induced magnetization time in multibunch operation of BESSY II. dynamics, which is a research focus within the MBI projects 3.2 and 3.3. Stretching of the pulses prior to amplification in the fiber amplifier is carried out with a variable grating stretcher. In contrast, final compression of the output pulses in T2: Terawatt OPCPA system both the main and the reference channel is done by two identical volume Bragg gratings (VBGs). This combina- The goal of this topic is to set up an OPCPA system tion leads to a compact pulse compressor, and allows that produces high-energy (E > 30 mJ) pulses with sub- for tuning of the pulse duration between <1 and 30 ps. 10 fs duration. With these pulses, we aim to generate The pulses are delivered to the sample in the vacuum high harmonics with pulse energy sufficient for attosec- chamber via an optical fiber to enable compatibility with ond XUV-pump XUV-probe experiments as well as for the x-ray optics of the STXM. In 2018, the major opti- time-resolved coherent diffractive imaging studies. cal components of the laser have been installed at the MAXYMUS lab at BESSY. The fiber-based pulse deliv- Our OPCPA design, which is depicted in figure 3, utiliz- ery system (Figure 3) will be installed in early 2019 al- es powerful thin-disk lasers as a pump source. This thin- lowing for subsequent commissioning and pump-probe disk laser system was developed during the previous x-ray microscopy. years in the framework of project 1.2.

83 Fig. 3: Scheme of the OPA system pumped by a thin-disk laser

In 2018, the work was focused on the following topics: losses, the pulses need to be negatively chirped to have a pulse-duration of approximately 5 ps in the OPCPA • Setup of a GRISM stretcher for the seed pulses amplification stages. Thus, an appropriate compression • Installation of a pointing stabilization for the seed requires compensation of the group delay dispersion beam (GDD) and higher dispersion orders. We have chosen • Setup of three OPCPA stages a combination of a GRISM (grating and prism pairs) and • Setup of a pulse compressor (glass and chirped mir- a programmable acousto-optic dispersive filter (DAZ- rors) ZLER) for the initial chirp management (see figure 5).

The seed beam delivered by the front-end covers a The GRISM pair introduces a controllable large nega- spectral range from 700 – 1050 nm, supporting a pulse tive GDD to stretch the pulses to 5 ps duration in the duration below 8 fs. In order to ensure a well behaved amplification stages. The compensating positive disper- amplification and a subsequent compression with low sion needed for final compression of the amplified pulses is induced by two large-diameter glass substrates, in combination with eight positively chirped mirrors. A 1 DAZZLER located after the GRISM compensates for the remaining third-order dispersion (TOD) from the GRISM, and allows for fine-tuning the spectral phase of the output pulse. This setup results in a duration of the output pulses below 9 fs.

Behind the DAZZLER less than 10 % of the initial pulse energy is left to be amplified in the optical parametric Arbitrary units chirped pulse amplification (OPCPA) setup. Based on simulations, the amplification of the seed pulse is done

700 800 900 1000 1100 with three stages of BBO crystals with thicknesses be- Wavelength [nm] tween 1.5 and 3 mm. The first stage is pumped with pulses of 15 mJ energy and ~ 8 ps duration and amplifies the pulse energy to the mJ level. Subsequently, the beam Fig. 4: diameter is increased by a factor of 3 to about 13.5 mm. Outpt spectrum of the front-end supporting a pulse dura- The next two OPCPA stages consist of BBO crystals with tion τ < 8 fs. 20 mm x 20 mm aperture. Both stages are pumped with pulses of 100 mJ energy and 8 ps duration. This leads

84 GRISM DAZZLER

5 ps ~ 100 fs 2-5 µJ 50 µJ ordinary axis

~ 25 ps 25 µJ

extraordinary axis

Fig. 5: Dispersion control of the seed beam utilizing a GRISM pair as well as a programmable acousto-optic dispersive filter (DAZZLER)

to an amplification of the signal pulses to an energy of ~20 mJ after the second and ~35 mJ after the third stage. Measurement To reduce the intensity in the subsequent compressor, 350 the beam diameter is further increased to about 67 mm. The 15 mm fused silica compressor glass is installed 400 as vacuum window of the compressor chamber. Figure 6 shows a FROG measurement of the amplified and 450 compressed pulse. The retrieved pulse duration is well

Wavelengt [nm] Wavelengt below 9 fs. 500

-100 0 100 The compressed pulse is guided in vacuum and fo- Time [fs] cused into a gas cell for generation of high harmonics. The appropriate results are described in the report of project 2.1. Retrieval

350 T3: High repetition rate OPCPA

400 Coherent light sources producing Carrier-Envelope Phase (CEP)-stable, few-cycle pulses at high average 450 power and high repetition rate are extremely attractive for a multitude of applications in strong field physics, Wavelengt [nm] Wavelengt 500 attosecond science, and novel approaches in material -100 0 100 processing, among others. In this activity we aim to de- Time [fs] velop such sources based on non-collinear OPCPAs seeded by a Ti:Sapphire oscillator.

1 10 Two systems are currently in operation: a 400 kHz OPCPA delivering CEP-stable few-cycle (˂ 7 fs) 10 µJ pulses, and a 100 kHz OPCPA with CEP-stable, 5 190 µJ few-cycle pulses (< 7 fs). Phase [rad] Norm. intensity Activities concerning the 400 kHz OPCPA and nonlinear 0 0 -50 -25 0 25 50 compression of pump pulses. Time [fs] During 2018 the system has been utilized for novel approaches in material processing (project 3.2). This ap- Fig. 6: plication does not make use of CEP stability. Moreover, FROG measurement of the amplified output pulse. The first experiments exploring the dependence of the ma- pulse duration is below 9 fs. terial modification with pulse duration suggest that the results do not depend strongly on the pulse duration for

85 pulses below ~ 50 fs. Therefore, experimental work on silica window. The initial pulse duration was 350 fs at direct nonlinear compression of laser pulses from a high 1030 nm. After spectral broadening the pulse spectrum repetition rate fiber amplifier has been started. This fiber supports 67 fs pulses. amplifier (or very similar) is what has been so far utilized to pump high repetition rate OPCPAs. The aim of this Activities concerning the 100 kHz OPCPA development is to provide a very compact, robust, and simple to operate source of ultra-short, high repetition The main application for the 100 kHz OPCPA is to drive rate laser pulses, for material processing applications. an attosecond pump-probe beamline with ion-electron In a proof-of-principle experiment, a Herriot-Cell was coincidence detection (project 2.1). In this context, the built, consisting of two 50 mm diameter spherical mirrors repetition rate is extremely important for fast data ac- (f = 250 mm) and two 12.5 mm diameter flat mirrors for cumulation with the coincidence detection apparatus, coupling in and out of the cavity. At the center of the cav- while the energy, pulse duration and CEP stability are ity where the beam waist is located, a 12 mm thick fused essential to generate high-order harmonics in the XUV, silica window was placed, to act as nonlinear medium and moreover, to confine the harmonic emission to a for spectral broadening. Figure 7 shows the pulse spec- single half cycle of the laser pulse in order to produce trum out of the Herriot-cell with and without the fused isolated attosecond pulses (IAP).

During 2018, 7 fs pulses from the OPCPA were uti- 1.0 lized to generate high-order harmonics in Ar, and the resulting trains of XUV pulses were characterized in 0.8 an XUV-IR pump-probe experiment (for details, see 0.6 project 2.1).

0.4 In order to generate isolated attosecond XUV pulses, the harmonic generation process was driven with 0.2

Norm. power density near-single-cycle pulses. With that aim, we performed 0.0 nonlinear compression of the 7 fs pulses out of the 1000 1010 1020 1030 1040 1050 1060 Wavelengt [nm] OPCPA in a hollow-core fiber (HCF) filled with 2.5 bars of Ne. Figure 8 shows the characterization of the com Fig. 7: pressed pulses utilizing the SEA-F-SPIDER tech- Spectral broadening after 20 passes in the Herriot-cell nique. with a 12 mm thick fused silica window placed in the position of the beam waist (blue trace). The original pulse A crucial aspect for the generation of IAP is the CEP spectrum is shown for comparison (red trace). stability of the laser pulses. During 2017 we had started a collaboration with the group of Prof. Gerhard Paulus

(a) (b) 100 100

50 50

0 0 x[µm] x[µm]

-50 -50

-100 -100 500 600 700 800 900 1000 1100 -60 -40 -20 0 20 40 60 Wavelengt [nm] Time [fs]

0.8 2 0.6 0

y [mm] 0.4 -2 0.2 Normalized intensity -4 0.0 -4 -2 0 2 4 -60 -40 -20 0 20 40 60 x [mm] Time [fs]

Fig. 8: Characterization of near-single-cycle pulses. a and b show the spectrum and temporal reconstruction of the pulse as a function of position (along one direction across the beam) respectively. C shows the beam profile after collimation and d shows the spatial integration over the spatio-temporal distribution shown in b (integration carried out over the shaded area in figure b).

86 Laser shot Laser shot Fig. 9: 0 5 10 0 1 x 106 2 x 106 (a)–(c) Top row with active oscillator 1.0 CEP stabilization only (open loop); 0.5 (d)–(f) middle row with stereo-ATI 00 CEP feedback on the oscillator; -0.5 and (g)–(i) bottom row f-2f CEP -1.0 feedback. The left column shows 1.0 the short-term trace over 200 μs, 0.5 and the middle column density plots 00 over 20s/2M shots with its histogram -0.5 in the right column. For the oscilla- CEP [ π rad] CEP -1.0 tor-stable-only case, the SD over 1.0 the 2M shots amounts to 399 mrad. 0.5 While also including the stereo-ATI 00 feedback, it is reduced to 252 mrad; -0.5 a trace with the f-2f feedback yields -1.0 297 mrad. Taken from Hoff, et al., 0 50 100 0 5 10 15 0 2 4 Optics Letters 43, 3850 (2018). Time [µs] Time [s] Counts [104]

pulse can be isolated. Moreover, the system has been utilized in pump-probe photoionization experiments com- 4 bining XUV and IR pulses with variable delays, in order 3 to characterize the XUV pulses. 2 1 CEP [ π rad] CEP 0 20 25 30 35 40 45 50 55 60 65 Invited Talks at International Conferences Photon energy [eV] (for full titles see appendix 2)

Fig. 10: F. J. Furch; OSA High brightess sources and light driven High harmonic spectra generated in Ar as a function of interactions congress 2018 (Strasbourg, France, 2018- the Carrier-Envelope Phase. 03)

F. J. Furch: IX International Conference for Profession- (Helmholtz-Institut Jena Institut für Optik und Quan- als and Young Scientists (Kharkiv, Ukraine, 2018-06) tenelektronik) in order to characterize the CEP stability of the pulses amplified in the OPCPA utilizing the stereo F. J. Furch; OSA Latin America Optics & Photonics con- Above-Threshold-Ionization (ATI) technique. In 2018, gress (Lima, Perú, 2018-11) the CEP measurements were improved with an overall improvement in the short and long term beam pointing and shot-to-shot energy stability of the OPCPA, and also, by utilizing shorter pulses from the HCF compressor. Publication

Figure 9 shows measured CEP values at the full rep- Publications which have emerged from work in this in- etition rate (100 kHz) when the oscillator is running frastructure project are listed under the relevant projects CEP-stable, utilizing the measured values from the ste- (1.2, 2.1, 2.2 and 3.2). reo-ATI to control slow drifts, and utilizing CEP values measured with an f-2f interferometer to perform the slow drift correction (integrating 100 pulses per measurement, measuring at 200 Hz).

With all the previously mentioned improvements, the CEP stable, few-cycle pulses have been utilized to generate XUV radiation through high-order harmonic generation. As an example, figure 10 shows high harmonic spectra as a function of the CEP. The XUV radiation was generated by focusing 75 µJ, sub-4 fs pulses to an ap- proximate intensity of 2x1014 W/cm2 into a 1 mm gas cell filled with Ar. The presence of a continuous spectrum for some values of the CEP suggests that a single XUV

87 4.2: Application Laboratories and Technology Transfer

Femtosecond Application Laboratories (FAL) U. Eichmann, T. Nagy, E. T. J. Nibbering, V. Petrov, N. Zhavoronkov

1. Overview The Multicolor-II lab offers a combination of frequen- Research at MBI requires a long term scientific infra- cy tunable pulses from the UV to mid-IR with few-cy- structure, interdisciplinary work and flexibility in the or- cle pulses from a 3-meter-long hollow-core fiber (HCF) ganization of scientific projects. Since two decades MBI compressor (Fig.1). The lab hosted two major experi- has concentrated some of its experimental resources ments both investigating high harmonics generation via in application laboratories, providing flexible, access to Brunel radiation in solids and gases. Furthermore, the expensive, state-of-the-art equipment for internal and development of a new arrangement for sub-10 fs deep external researchers, in particular also serving collabo- UV pulse generation has been started. ration and access programs. MBI offered access to the following femtosecond laboratories: The UV/MIR application laboratory has been used to further explore proton transport dynamics of bifunction- • MultiColor fs-system-I al photoacids in protic solvents like methanol, water or • MultiColor fs-system-II their mixtures in the context of Project 3.1. • UV/MIR fs-system • Few cycle and tailored pulses The main activities at the FAL “Few cycle and tailored • 80 MHz fs-system pulses” were devoted to the use of two-colour few cycle pulse capabilities. Attosecond pulses with tunable ellip- In light of the changed demands of user experiments, ticity and programmable helicity were generated, with a which ever more frequently ask for access to a com- clear perspective to reach the regime of isolated atto- plete laboratory infrastructure including experimental second pulse generation. Experiments to determine the setups, rather than access to laser systems only, MBI residual phase distortion in the interaction region of sub- has in 2018 decided to abolish the FAL in their previ- two-cycle laser pulses with a gaseous target have been ously existing form, and now operates most of its laser carried out via HHG spectroscopy. A OPA TOPAS Prime laboratories as on-demand application laboratories. In was implemented in the setup expanding the ability of this way, external researchers can benefit from the latest the laboratory towards NIR radiation down to 2500 nm. developments and expertise at MBI for their research. In the future, MBI will concentrate on two dedicated application laboratories, BLiX and NanoMovie. Trans-national access to all these MBI laboratories is facilitated by 2. User statistics 2018 the Laserlab-Europe access programs. In 2017 the internal use of the FAL by 7 project groups Examples of 2018 activities are: was 70 % of the available access time (from KLR statistics). In estimated ~20 % of the time external guests At the Multicolor-I system, experiments within the frame- were involved in the experiments. We had 9 visiting sci- work of two projects have been performed. Project 3.1 entists in 2017 from China, Russia and Spain, support- pursued experiments on time-resolved photoelectron ed by the EC (LaserLab) or foreign funding programs. spectroscopy on hydrated molecules. A new setup for time-resolved photoelectron circular dichroism has been installed and first promising experiments on fenchone - a chiral model system - have already been performed as Publication feasibility tests. As reported in project 2.2, the Multicol- or-I system was used to study strong-field excitation and All publications which have emerged from work in the acceleration of atom and molecules [ZMK18]. FAL are listed under the relevant research projects.

Fig. 1: After a rearrangement, the Multi- color-II lab offers more space for users. The existing commercial system has been upgraded with in-house developed pulse compression technology.

88 NanoMovie – Application Laboratory for nanoscopic spectroscopy and imaging M. Schnürer (project coordinator), L. Ehrentraut, T. Feng, P. Friedrich, G. Kommol, Ch. Strüber, M. van Mörbeck-Bock

1. Overview 2. Results in 2018

The goal of the NanoMovie project is to establish an ap- The design for the NanoMovie 2.1 µm laser features plication laboratory where soft x-rays with photon ener- a monolithic concept, deriving the seed and the pump gies in the water window (about 300 to 500 eV) and be- beam for the OPCPA stages from the same pump laser. yond are reliably generated with high stability for use in This approach takes advantage of the fact that suitable application experiments. The project started in Novem- pump lasers and frontend systems for signal generation ber 2016, when cofinancing through the “European Re- have recently become commercially available. gional Development Fund – ERDF” could be secured, for a project duration of four years in total. When operational, the NanoMovie laboratory will enable fundamental and applied research with ultrashort soft x-rays pulses. Focus areas are

• nanospectroscopy and imaging with coherent soft X-rays • study of dynamical processes at the nanometer scale • providing an experiment and testing platform for external users, including SMEs • development of laser-based soft x-ray technology 1 As a key ingredient, the project includes the development of two suitable, high average power laser systems for the efficient generation of soft x-rays via high har- 0.5 AC [a. u.] monic generation (HHG) as well as the shaping and delivery of the radiation via suitable optics to experimental 0 endstations for spectroscopy, scattering and imaging. -6 -4 -2 0 2 4 6 The philosophy is to create a stable source of femto- Delay [ps] second soft x-ray pulses for applications, using reliable commercial components where possible. While there Fig. 1: has been substantial progress in reaching higher pho- (top) 500 W beam on measurement head, desktop ton energies in pioneering HHG experiments, the limited screenshot from the DIRA 500 control program: the photon flux has so far precluded a widespread applica- standard deviation of the output laser pulse energy at tion. The decreasing photon flux when increasing the photon energy from the VUV to the soft x-ray regime 10 kHz is less than 1 % during daily operation; (bot- is a consequence of the HHG- process itself. Access- tom) temporal pulse durations of the high power and ing the soft x-ray region requires IR driver lasers with low power output obtained in operation at MBI. longer wavelength, balancing the photon energy and photon flux generated. After the design of a 2.1 µm OP- CPA laser and the procurement of key components with Pumplaser: A 500 W Thin Disk Laser (TDL) DIRA500 long lead times the system construction could start in by Trumpf Scientific GmbH has been installed in sum- mid-2018. The pump-laser and frontend purchased are mer 2018. It delivers pulses with up to 50 mJ energy at “first of its kind” products and an extended period of bug ~ 1 ps temporal duration and a wavelength of 1030 nm. fixing and commissioning followed which is still, at the The pulse repetition rate is variable between 5, 10 or beginning of 2019, not completed. Nevertheless, OPA 20 kHz. In comparison to systems with higher repeti- experimental work for the 2.1 µm wavelength and de- tion rates these parameters allow for the generation sign work for the second system, a 3 µm OPCPA laser, of IR-pulses with few mJ pulse energy and thus the started, with procurement procedures for the latter start- possibility to achieve the necessary intensity for HHG ing in 2019. The system design was established within in a suitable focussing geometry. After installation, the a larger group of OPCPA experts connected to projects DIRA500 had severe power-loss and stability issues 1.2 and 4.1. The NanoMovie application laboratory is leading to multiple operation disruptions within the first established in the rooms of the former High Field Appli- 6 months of operation, forcing the company and MBI cation Laboratory, which was completely reconstructed team to spent significant time on the analysis and fix- in 2017 for this purpose ing of the problems. By the end of the year, the problems had been solved. In Fig.1 we show a screenshot from the DIRA control program demonstrating the ap-

89 propriate energy output in 10 kHz operation with a long of the frontend we could just realize first amplification term pulse energy variation being clearly below 1 %. In within the OPA-1 stage. At about 110 W effective pump addition to this high power (HP) output, a 0.5 mJ low power, we achieved amplification to 10 W @ 10 kHz of power (LP) output with extra pulse compression and in- the 2.1 µm pulses with a good beam profile. Experimen- tensity stabilization serves to pump the frontend of the tal results are depicted in Fig. 3, they are in accordance OPCPA-system. The temporal pulse characteristic of LP with the simulation considering the currently reduced (< 1 ps) and HP (~ 2 ps) output is also shown in Fig. 1. power and limited spectral bandwidth of the frontend.

Frontend: Signal generation around a center-wavelength of 2100 nm is realized with a frontend system which 1.0 is developed by Fastlite. The system uses the 0.5 mJ pulses from the DIRA500 LP output and produces IR 0.8 pulses at about 30 μJ via white-light generation followed by frequency mixing and optical parametric amplification 0.6 (OPA). Such a concept is possible because the DIRA LP 0.4 output is sufficiently short (< 1 ps) in pulse duration and sufficiently stable in intensity. In Fig. 2 we show a part 0.2 of the frontend during operation and the spectrum of the 0.0 output pulses at optimum conditions, allowing for pulse 1600 1800 2000 2200 2400 2600 compression down to 20 fs. Normalized intensity Wavelength [nm] Signal count 2500 10.00 2400 8.75

2300 7.50 6.25 2200 5.00 2100 3.75 2000 2.50 1900 800 1.25

Wavelength [nm] Wavelength 1800 0.00 500 -3100 -3050 -3000 -2950 -2900 Time delay [arb. u.] 400

300 Fig. 3: 200 (top) Spatial intensity distribution and measured spectrum of the 10 W uncompressed beam in comparison

Intensity [arb. units] 100 with an OPA simulation with the following parameters: 0 seed pulse energy: 20 μJ, pump intensity: 70 GW/cm2, 1600 1800 2000 2200 2400 2600 2800 beam diameter: 5 mm, pump pulse duration: 2 ps, Wavelength [nm] seed pulse duration: 1 ps, maximum pump pulse en- Fig. 2: ergy: 15 mJ, BiBO-crystal thickness: 2 mm, resulting (top) Photograph of the frontend during operation; maximum amplification is from 20 μJ to 1.2 mJ per (bottom) at optimum conditions the measured spec- pulse (corresponding to 12 W); (bottom) measured trum allows for pulse compression down to a temporal spectral amplification versus time delay between seed duration of 20 fs. and pump.

Currently, the stability of the frontend is insufficient to With optimum frontend conditions an additional 1.5 fold provide pulses to the specified parameters during rou- increase of power is possible at this stage. Further work tine operation; also the carrier phase stabilization of the is devoted to pulse stretching and compression as well pulses has not been demonstrated so far. Therefore, a as to the setup of the final power OPA stage. We antici- partial frontend reconstruction by the Fastlite company pate that we can arrive at a final pulse duration of about is in progress. 25 fs for pulses with a central wavelength of 2100 nm and an average power of 30 W – 50 W at 10 kHz repe- OPA-stages: The signal pulses from the frontend at tition rate. around 400 fs pulse duration will be stretched further to about 1 ps and will be subsequently amplified in two Concept for a 3 µm OPCPA system: Based on current OPA stages pumped by the DIRA500. We realized a knowledge the realization of HHG to photon energies scheme with rather small (1-2 degree) non-collinear an- beyond the water window with appreciable flux requires gles between pump and signal. Such a geometry allows even longer wavelength for the laser driver. We will pur- keeping the bandwidth of the signal pulse at a maximum sue the realization of a 3 µm system which can be also together with a low spatial chirp and avoids pulse front realized with a monolithic pump concept on basis of a tilt in the signal. With the currently limited performance 1030 nm Yb:YAG TDL DIRA laser, allowing for technol-

90 Fig. 4: Simulation of amplified pulse Normailzed signal near field fluence and beam shape for a ~ 3 μm 1.0 4 OPA stage using a KTA-crys- 3 tal: phase mismatching angle: 0.8 2 41.8°, non-collinear angle: 6°, 2 0.6 1 pump intensity: 70 GW/cm , 0 beam diameter: 6 mm, pump pulse duration: 2 ps, seed 0.4 -1 y position [mm] pulse duration: 1 ps, pump -2 0.2 pulse energy: 15 mJ, crystal Normalized intensity [a. u.] -3 thickness: 1 mm, pulse dura- 0.0 -4 tion of amplified pulse – -4 -3 -2 -1 0 1 2 3 40 fs, resulting maximum Delay [ps] x position [mm] amplification is from 0.15 mJ pulse energy to 1 mJ.

ogy redundancy in the project. A very recent demonstration of such a system with 100 kHz repetition rate was published by ELI-ALPS and Fastlite. Again, we favor a repetition rate allowing above 1 mJ output energy for the 3 μm IR-pulse. Comprehensive simulations of the parametric amplification (cf. results in Fig. 4) were carried out for a design using the specific frontend from FASTLITE in combination with a power OPA-stage. Due to con- straints given by suitable crystals, we are considering a system with 20 kHz repetition rate, an option provided by the DIRA 500.

OPA simulations were carried out by T. Feng in collaboration with G. Arisholm, Forsvarets forskningsinstitutt, using the Sysifos software.

3. Users and publications

Infrastructure is under construction.

91 Berlin Laboratory for innovative X-ray Technologies (BLiX)

H. Stiel (project coordinator)

1. Overview spectrometer combining a probe and a reference channel (collaboration with HZB and NOB GmbH, Berlin) for near The Berlin Laboratory for innovative X-ray Technolo- edge X-ray absorption fine structure (NEXAFS) spectros- gies (BLiX, www.blix.tu-berlin.de) is jointly operated by copy investigations with a spectral resolution up to E/ΔE = the Institut für Optik und Atomare Physik (IOAP) of the 1000 at the carbon K-edge. Technische Universität Berlin and the Max-Born-Institut. BLiX is the „Leibniz-Applikationslabor“ of MBI. It oper- Laboratory X-ray microscopy ates at the interface of scientific research and industrial application with the goal to transfer research results into The full field laboratory transmission X-ray microscope instrument prototypes, with a focus on instruments and (LTXM) operated at BLiX enables the detection of high techniques that can be used in a laboratory environment quality nanoscopic images at 500 eV with a magnifica- without the need for large scale facilities. BLiX is sup- tion up to 1000 in a field of view of about 30 µm, a spatial posed to be a place of collaborative technology develop- resolution of 30 nm and a typical data accumulation time ment in the knowledge triangle of research – innovation of less than one minute. – education. The soft X-ray radiation of the LTXM is provided by a The main fields of activity in BLiX are: laser-generated plasma. A pulsed Nd:YAG laser beam (1.3 kHz repetition rate, 0.5 ns pulse duration, average • Soft x-ray imaging using laboratory X-ray microscopy power ≤ 130 W) is focused onto a nitrogen cryo-jet. Line • Confocal micro X-ray fluorescence analysis emission from the resulting hot dense plasma is collect- • Detection of chemical speciation ed by a multilayer condenser mirror, monochromatized • Soft X-ray absorption spectroscopy in the laboratory and focused on the sample. Behind the sample, a zone • Customer inspired development of hard X-ray plate objective, projects the image onto a cooled back spectrometers based on highly annealed pyrolytic illuminated X-ray CCD-Camera. We used two camera graphite optics. systems. For soft X-ray tomography, a commercially available scientific CCD detector is attached to the MBI contributes to BLiX predominantly via: LTXM. A prototype of a super resolution (SR) camera developed by greateyes GmbH in collaboration with MBI • the support of development and operation of a soft was utilized for SR imaging. X-ray absorption spectroscopy beamline based on a laser produced plasma X-ray source and novel X-ray The LTXM is equipped with a high-precision cryo-stage optics; for the sample which allows tomographic measure- • the upgrade of a full field laboratory transmission x-ray ments. microscope (LTXM) capable of tomographic nanoscale imaging and support of LTXM user operation; • the transfer of know-how concerning the development and application of laser based sources, optics and 2. Results in 2018 detectors for the soft and hard X-ray region. Results with direct participation of MBI personnel Near-edge X-ray absorption fine structure spectroscopy in the laboratory NEXAFS spectroscopy in the photon energy range 200– 600 eV A laser produced plasma (LPP) source based on long time experience of MBI in laser plasma dynamics has been In order to make NEXAFS spectroscopy in the lab avail- implemented at BLiX in collaboration between IOAP/TU able to a community mainly interested in investigations Berlin and BESTEC GmbH. The LPP source delivers soft on organic molecules, the work in 2018 has been fo- x-ray pulses in the photon energy range between 100 and cused on both improvement in sample preparation tech- 1000 eV with 1 ns pulse duration, 100 Hz repetition rate niques for this class of molecules and improvement of and a maximum average brightness in selected emission the spectrometer setup. lines of up to 1011 ph/s*mm2*mrad2. The sample preparation for NEXAFS investigations in For investigations of samples relevant for users from life transmission mode as applied in our spectrometer is and environmental sciences an X-ray absorption beam- challenging. There are two main issues: i) keep sample line has been implemented. The beamline is equipped integrity during the preparation process and ii) control with a novel two-channel reflection zone-plate (RZP) the optimum sample thickness. We have applied two

92 approaches for sample preparation: i) an effusion cell trum expected after excitation by an optical pump pulse. technique for preparation of thin biomolecular films on Pump-probe NEXAFS investigations at the carbon and silicon nitride windows and ii) a spin coating technique nitrogen K-edge together with TDFT calculations could for preparation of thin films containing e.g. nanoparti- help to understand e.g. the strong excitonic coupling in cles. To check the sample integrity after the preparation the PIC J-aggregates in more detail. In order to enable process we used UV/VIS spectroscopy. The sample pump-probe measurements, the NEXAFS setup was thickness after the preparation process can be checked complemented with an optical beamline and a delay by two independent methods available at MBI, atomic stage and first test measurements are under way. force microscopy (AFM, collaboration with project 4.3) and extreme ultraviolet (EUV) imaging.

The spin coating technique has been successfully ap- 1.25 plied to produce thin films of anatase TiO2 films with a precisely specified thickness. These films are of great 1.00 technological relevance e.g. in photocatalytic processes. NEXAFS investigations on the Ti L-edge and O 0.75

K-edge of these films are currently in progress. [µd] 0.50 Evaporation using an effusion cell was applied for thin 0.25 film production of organic molecules. We explore the potential of this technique for different classes of organic 0.00 molecules (e.g. porphyrins, xanthenes and cyanines). 275 280 285 290 295 300 305 310 315 NEXAFS investigations of porphyrins and xanthenes Energy [eV] thin films are part of the DFG project #313838950 (I. Mantouvalou, TU Berlin). Fig. 2: NEXAFS spectrum of a PIC thin film prepared by effu- [µm] sion cell technique. Thickness of the film as estimated 0 2 4 by AFM and EUV imaging: 300 nm. The NEXAFS spec- 0 2.03 trum was obtained with the RZP spectrometer at BLiX. Recording time: 3 s (300 shots at 100 Hz laser repeti- 1.50 tion rate). (L. Glöggler, MSc thesis, TU Berlin, 2019)

2 1.00

[nm] Nanoscale imaging in the water window

In June 2018, the Collaborative Research Center 0.50 4 (CRC) 1340 ”Matrix in Vision” was established by the German Science Foundation DFG, focusing on how 0.00 pathological changes of the extracellular matrix can be visualized by techniques available in diagnostic radiol- ogy. Fig. 1: The CRC combines different biological molecular AFM image of 5x5 μm2 subset of the PIC sample sur- methods and imaging techniques such as optical and

face on a Si3N4 membrane. Please note that the film X-ray microscopy, magnetic particle imaging and mag- thickness is about 300 nm. netic resonance imaging, in order to obtain insight into (L. Glöggler, MSc thesis, TU Berlin, 2019) the role of mechanical tissue parameters in the development of disease. BLiX researchers contribute to the CRC 1340 via studies of the 3D localization of marker J-aggregates of organic molecules such as pseudoiso- nanoparticles in biological matrices using the LTXM. cyanine (PIC) offer unique possibilities in developing In order to meet the performance requirements, work e.g. new fluorescence based sensing techniques. Fur- in 2018 concentrated on improving the LTXM stability thermore, J-aggregates exhibit striking nonlinear optical and optimizing the photon flux of the source. Further- properties (e.g. strong excitonic coupling due to a large more, conventional fluorescence visible-light micros- intermolecular delocalization of the excitation energy copy (FLVM) has been implemented in order to enable leading to a “giant” transition dipole moment). We have correlative studies connecting to standard medical lab prepared and characterized films of PIC with a precisely techniques. defined thickness. In Fig. 1 we show an AFM image of a thin PIC film prepared by evaporation technique. The NEXAFS spectrum as recorded with the two-channel Results by TU Berlin personnel, without participa- RZP spectrometer is presented in Fig. 2. Note that the tion of MBI scientists signal to noise ratio (SNR) in the post-edge region is about 80, corresponding to a measurable difference in In the following, results by non-MBI staff within BLiX are optical thickness on the order of 10-2. This is a prerequi- briefly summarized to allow for a complete picture of the site for the detection of the small changes in the spec- BLiX activities.

93 The instrumentation for X-ray spectroscopy and micros- The long term cooperation with the X-ray Spectrometry copy developed in BLiX has reached a state where it group (Dr. Burkhard Beckhoff) at PTB was continued. can be used in applications. Currently, BLiX researchers In joint experiments with PTB, Bruker Nano and BLiX, develop one NEXAFS and one XANES spectrometer laboratory methods were evaluated and validated us- for research at the Max-Planck-Institute for Chemical ing calibrated instrumentation at the PTB laboratory at Energy Conversion. Within BLiX, the current emphasis BESSY II. is on performing demonstration applications in order to facilitate further commercialization of the instruments with companies. Therefore, interdisciplinary research collaborations were a focus of BLiX activities in 2018, in 3. Users and collaborations addition to the ongoing development activities. Charité Berlin, Germany; McGill University, Montreal, Ongoing and newly initiated research collaborations are Canada; University of Ljubljana, Slovenia; The Arctic listed below. University of Norway, Tromsö; Institute for Chemistry, TU Berlin, Germany; Julius Wolf Institute, Charité, Berlin X-ray absorption spectroscopy (XANES, EXAFS) Max-Planck-Institute for Chemical Energy Conversion; FhG-ILT, Aachen, Germany; optixFab GmbH, Jena, The BLiX spectrometer is capable of producing XANES Germany; greateyes GmbH, Berlin, Germany; HZB/ spectra with moderate energy resolution and excellent BESSY, Berlin, Germany; PTB, Berlin, Germany; KTH, EXAFS spectra within reasonable acquisition times. On- Stockholm, Sweden; BESTEC GmbH, Berlin; nano op- going application projects are: tics berlin (nob) GmbH, Berlin, Germany; Excillum Ltd, Kista, Sweden; Helmut Fischer GmbH (IFG), Berlin/Sin- • Analysis of water sediments (Dr. Michael Hupfer, Leib- delfingen, Germany; Optigraph GmbH; Université Pierre niz Institut für Gewässerökologie und Binnenfischerei) et Marie Curie, CNRS, Paris, Frankreich • Quantitative analysis of species mixtures (Prof. Dr. Carla Vogt, Technische Universität Bergakademie Freiberg) • EXAFS in industrial applications (Prof. Dr. Iztok Ar- People con, University of Nova Gorica) MBI: Julia Bränzel, Johannes Tümmler, Pascal Engl Confocal micro-X-ray fluorescence spectroscopy (XRF) TUB: Aurélie Dehlinger, Christian Seim, Ioanna Man- touvalou, Adrian Jonas, Daniel Grötzsch, Christopher A dedicated laboratory for micro-XRF and confocal Schlesiger, Wolfgang Malzer, Birgit Kanngießer micro-XRF is operated within BLiX. In 2018, the main focus was on biological samples, including the investigation of cryo-fixated samples. Ongoing application projects focus on:. Publication

• Metal distribution in mussel tissue for the elucidation All publications involving MBI scientists which have of the formation of byssus threads emerged from work in BLiX are listed under the relevant • Uptake of heavy metals in corn and sunflower roots/ research projects (cp. Project 3.3). shoots/leaves as a mean to illuminate metal transport in plants Publications related exclusively to TU Berlin personnel, • Mineral exchange between host plant and cuscuta without contribution of MBI scientists parasite • Shape and distribution of Pt patches in self-activated W. Malzer et al.; Rev. Sci Instr. 89 (2018) 113111 catalysis particles • Interface dynamics in teeth close to restauration J. Baumann et al.; J. Anal. At. Spectrom. 33 (2018) 2043-2052 In a cooperation with Excillum Ltd. and Helmut Fischer GmbH, new experiments were initiated to assess the L. Bauer et al.; J. Anal. At. Spectrom. 33 (2018) 1552- performance of high brilliance metal jet sources in con- 1558 junction with polycapillary optics A. Jonas et al.; Rev. Sci Instr. 89 (2018) 026108 Angle-resolved X-ray fluorescence spectroscopy (XRF)

Three different setups for angle-resolved XRF are operational, in part with custom hardware solutions developed at BLiX. While the main focus is still on the improvement of the setups, a first application project could be carried out:

• Inter- and intra-layer diffusion processes in water window multilayer optics

94 4.3: Nanoscale Samples and Optics

D. Engel (project coordinator), D. Sommer, S. Petz Nanna Zhou Hagström (U. Stockholm/guest), C. Günther (TU Berlin/guest)

1. Overview sample in conjunction with spectroscopy, scattering or imaging methods allows for designing unique experi- The Laboratory for Nanoscaled Samples and Optics ments with specifi c information content and sensitivity, supports several experiments in different scientifi c pro- for example via integrated near fi eld optics. jects of the MBI. We produce thin-fi lm samples, fi lters and membranes by means of magnetron sputtering and Furthermore, via nanopatterning we are able to produce thermal evaporation. The deposition system enables the diffractive far fi eld optics for experiments with XUV and coating of up to 4" substrates using a maximum of eight soft x-rays, where structure sizes have to approach the different materials without vacuum break. Lateral pat- wavelength of the radiation in use. Custom Fresnel zone terning of samples on the micrometer and/or nanometer plates, holographic masks or coded aperture arrays are scale is achieved via electron beam lithography or Fo- some examples of these capabilities. cused-Ion-Beam (FIB) patterning, in close cooperation with the central facility for electron microscopy (ZELMI) Finally, the study of ultrafast dynamic processes in mag- at the TU Berlin. Topographic and magnetic characteri- netic materials requires the development of suitable zation of thin fi lm samples is carried out by atomic- and sample materials in the form of thin multilayer fi lms or al- magnetic force microscopy (AFM/MFM), Kerr mag- loys, together with the ability to characterize their static netometry (MOKE) and via Kerr microscopy. properties prior to time-resolved experiments.

Collaborations: Various scientists at the ZELMI (TU Ber- lin), M. Albrecht (Augsburg University), M. Schmidbauer (Leibnitz Institute for Crystal Growth), F. Kronast (Helm- 3. Results in 2018 holtz-Zentrum Berlin), R. Ernstorfer (Fritz-Haber-Institut). Terahertz magnetic fi eld enhancement in an asymmetric spiral metamaterial (cooperation with S. Bonetti, Stockholm University) 2. Objectives The motivation is to develop antenna structures to en- A variety of research activities at MBI deal with dynami- hance the magnetic fi eld component of a THz pulse cal processes which occur intrinsically on the nanometer within the central gap of such a structure, such that a length scale set by fundamental material properties such sample to be investigated can be placed there for pump- as inelastic mean free paths for transport of electrons or probe experiments. Towards this end, we investigate the spins. Sensitivity to such processes can be obtained via performance of a simple asymmetric and a spiral split- several experimental approaches using short pulses of ring resonator. First, we use fi nite element simulations in optical light, XUV or x-rays. Nanoscale patterning of a both the frequency- and the time-domain to investigate

Electric fi eld Magnetic fi eld Fig. 1: enhancement enhancement Simple asymmetric 10 10 split-ring resonator. Upper panels: enhance- 0 0 ment map for (a) THz

y [µm] y [µm] electric and (b) THz magnetic fi elds at the -10 -10 metamaterial surface, at 1.4 THz. Lower panels: -10 0 10 20 -10 0 10 20 enhancement of the x [µm] x [µm] THz electric (c) and magnetic (d) fi elds in 20 20 the direction lx parallel Electric fi eld enhancement 15 15 to the arm (solid line), and the direction ly per- 10 10 pendicular to the arm Magnetic fi eld enhancement Enhancement 5 Enhancement 5 (dashed line).

0 0 -4 -2 0 2 4 -4 -2 0 2 4 Position [µm] Position [µm]

95 Fig. 2: 40 100 Spiral split-ring resonator. 90 35 The (a) electric and (b) mag- 80 30 netic fi eld enhancement (with respect to the incident fi eld) 70 25 at the metamaterial plane 60 20 observed from the frequency 50 15 domain analysis. The en- 40 hancement as function of fre- Enhancement 30 10 quency is shown in (c). The 20 5 white dot in (a) and (b) is the

10 0 origin of the spiral, where the 0 0.6 0.8 1.0 1.2 1.4 1.6 enhancement in the time do- Frequency [THz] main simulation is calculated.

gap, and it is much larger than the electric fi eld enhancement. Furthermore, the electric fi eld is predominantly enhanced in the outer annular region and at the outer edge of the spiral resonator, with only a slight enhancement in the central gap of the spiral. This is more obvious from Fig. 2(c), where we plot the enhancement factor at the center of the spiral as obtained by the Fourier transform of the simulated time-domain traces. It can be clearly seen that the electric fi eld enhancement is about a factor 5, while the magnetic fi eld enhancement reaches almost a factor of 40.

Based on these simulations, an experimental realization of a resonator array from 100 nm thick gold split-ring resonators is shown in Fig. 3. In the middle of each resonator a circular area with the magnetic layer (Ta(2)/ [Pt(2)/Co(0.4)]x5/ Pt(2)) to be investigated is deposited. The whole structure consists of an array of 10 x 10 resonators with a 100 µm pitch. Using direct laser writing and e-beam lithography, the array of magnetic dots was patterned from a continuous thin fi lm grown by sputter deposition. In a subsequent processing step, the gold resonators were lithographically defi ned. Helicity dependent all-optical magnetization switching at 800 nm in the continuous fi lm has been carried out via spatially resolved pump-probe experiments using time resolved Kerr microscopy in preparation for the planned experi- Fig. 3: ments on THz magnetic fi eld induced dynamics using First production result of the metastructure with an ar- the resonator structures. ray of 10 x 10 resonators. Each split-ring-resonator is made of 100 nm Au with a circular layer system con- As well we realized several dipole antenna structures

sisting of Ta(2)/[Pt(2)/Co(0.4)]x5/Pt(2). made of gold directly on ZnTe(110) crystals to enhance the electric fi eld of transmitted THz pulses. Further activities in project 4.3 concentrated on the optimization and optimize the three-dimensional distribution of elec- of magnetic multilayers and alloys for all-optical mag- tric and magnetic fi elds in such structures. netization switching and on layer systems, which serve e.g. as absorption standard for NEXAFS, as polariza- The simulated enhancement of the THz electric and tion fi lter for a plasma soft x-ray source, or as a mag- magnetic fi eld at 1.4 THz driver frequency for the sim- netic maze domain system with defi ned domain sizes for ple split-ring-resonator is shown in Fig. 1(a) and (b), scattering experiments. Furthermore, an important part respectively. The THz magnetic fi eld is strongly en- of our activities focused on the fabrication of near-fi eld hanced close to the Au ring, and most signifi cantly masks for Fourier transform holography experiments adjacent to the inner edge of the ring. The enhance- to investigate magnetic skyrmions. Closely related to ment maps for the electric and the magnetic fi elds at this activity, we thinned bulk samples to XUV trans- the surface of the metamaterial for the spiral split-ring parency to prepare nanoscale transmission imaging ex- resonator are the plotted in Fig. 2(a) and (b), respec- periments. Finally, we designed and produced grating tively, using the same color scale. The magnetic fi eld structures on Si3N4 membranes acting as fl uence moni- enhancement is moderately uniform over the central tor and beam profi ler in scattering experiments.

96 0 1 1 20 0.8 0.8 40

0.6 0.6 60

x [µm] 0.4 0.4 80

0.2

100 0.2 Norm. magnetization [M]

0 120 0 0 50 100 -1 0 1 2 3 y [µm] Time [ps]

Fig. 4:

TR-MOKE measurement of the Ta(2)/[Pt(2)/Co(0.4)]x5/Pt(2) magnetic fi lm used for the split-ring resonator MM.

Publication

PZK18: D. Polley et al.; J. Phys. B 51 (2018) 224001

Other Publication

D. Polley et al.; J. Phys. D: Appl. Phys. 51 084001

Further publications are listed in the context of the Pro- jects 3.2 and 3.3.

97 98 Appendices

99 Appendix 1 Publications

ABA18: F. Allum, M. Burt, K. Amini, R. Boll, H. Köckert, BBI18: D. Busto, L. Barreau, M. Isinger, M. Turconi, C. P. K. Olshin, S. Bari, C. Bomme, F. Brauße, B. Cunha Alexandridi, A. Harth, S. Zhong, R. J. Squibb, D. Kroon, de Miranda, S. Dusterer, B. Erk, M. Geleoc, R. Gene- S. Plogmaker, M. Miranda, Á. Jiménez-Galán, L. Argen- aux, A. S. Gentleman, G. Goldsztejn, R. Guillemin, D. ti, C. L. Arnold, R. Feifel, F. Martín, M. Gisselbrecht, A. M. P. Holland, I. Ismail, P. Johnsson, L. Journel, J. Kup- L’Huillier, and P. Salières; Time-frequency representa- per, J. Lahl, J. W. L. Lee, S. Maclot, S. R. Mackenzie, tion of autoionization dynamics in helium; J. Phys. B 51 B. Manschwetus, A. S. Mereshchenko, R. Mason, (2018) 044002/1-12 J. Palaudoux, M. Novella Piancastell, F. Penent, D. Rom- potis, A. Rouzée, T. Ruchon, A. Rudenko, E. Savelyev, BBM18: J. Braenzel, M. D. Barriga-Carrasco, R. Mo- M. Simon, N. Schirmel, H. Stapelfeldt, S. Techert, rales, and M. Schnürer; Charge-transfer processes in O. Travnikova, S. Trippel, J. G. Underwood, C. Vallance, warm dense matter: selective spectral filtering for la- J. Wiese, F. Ziaee, M. Brouard, T. Marchenko, and D. ser-accelerated ion beams; Phys. Rev. Lett. 120 (2018)

Rolles; Coulomb explosion imaging of CH3I and CH2ClI 184801/1-6 photodissociation dynamics; J. Chem. Phys. 149 (2018) 204313/1-10 BCD18: S. Beaulieu, A. Comby, D. Descamps, B. Fab- re, G. A. Garcia, R. Géneaux, A. G. Harvey, F. Légaré, ADP18a: D. Ayuso, P. Decleva, S. Patchkovskii, and O. Z. Mašín, L. Nahon, A. F. Ordonez, S. Petit, B. Pons, Smirnova; Chiral dichroism in bi-elliptical high-order har- Y. Mairesse, O. Smirnova, and V. Blanchet; Photoexci- monic generation; J. Phys. B 51 (2018) 06LT01/1-7 tation circular dichroism in chiral molecules; Nat. Phys. 14 (2018) 484-489 ADP18b: D. Ayuso, P. Decleva, S. Patchkovskii, and O. Smirnova; Strong-field control and enhancement of BCJ18: R. Y. Bello, S. E. Canton, D. Jelovina, J. D. Boz- chiral response in bi-elliptical high-order harmonic gen- ek, B. Rude, O. Smirnova, M. Y. Ivanov, A. Palacios, and eration: an analytical model, Special issue celebrating F. Martín; Reconstruction of the time-dependent elec- 25 years of re-collision physics; J. Phys. B 51 (2018) tronic wave packet arising from molecular autoioniza- 124002/1-13 tion; Sci. Adv. 4 (2018) eaat3962/1-6

AKW18: Z. Abdelrahman, M. A. Khokhlova, D. J. Walke, BGA18: F. Brauße, G. Goldsztejn, K. Amini, R. Boll, S. T. Witting, A. Zair, V. V. Strelkov, J. P. Marangos, and J. Bari, C. Bomme, M. Brouard, M. Burt, B. Cunha de Mi- W. G. Tisch; Chirp-control of resonant high-order har- randa, S. Düsterer, B. Erk, M. Géléoc, R. Geneaus, A. monic generation in indium ablation plumes driven by Gentleman, R. Guillemenin, I. Ismail, P. Johnsson, L. intense few-cycle laser pulses; Opt. Express 26 (2018) Journel, T. Kierspel, H. Köckert, J. Küpper, P. Lablam- 15745-15758 quie, J. Lahl, J. W. L. Lee, S. R. Mackenzie, S. Maclot, B. Manschwetus, A. S. Mereshchenko, T. Mullins, P. K. ASA18: M. V. Arkhipov, A. A. Shimko, R. M. Arkhipov, I. Olshin, J. Palaudoux, S. Patchkovskii, F. Penent, M. No- Babushkin, A. A. Kalinichev, A. Demircan, U. Morgner, vella Piancastelli, D. Rompotis, T. Ruchon, A. Ruden- and N. N. Rosanov; Mode-locking based on zero-area ko, E. Savelyev, N. Schirmel, S. Techert, O. Travnikova, pulse formation in a laser with a coherent absorber; La- S. Trippel, J. G. Underwood, C. Vallance, J. Wiese, M. ser Phys. Lett. 15 (2018) 075003/1-7 Simon, D. Holland, T. Marchenko, A. Rouzée, and D. Rolles; Time-resolved inner-shell photoelectron spec- ASB18: K. Amini, E. Savelyev, F. Brausse, N. Berrah, C. troscopy: from a bound molecule to an isolated atom; Bomme, M. Brouard, M. Burt, L. Christensen, S. Düsterer, Phys. Rev. A 97 (2018) 043429/1-10 B. Erk, H. Höppner, T. Kierspel, F. Krecinic, A. Lauer, J. W. L. Lee, M. Müller, E. Müller, T. Mullins, H. Redlin, N. Schir- BGG18: M. Bock, L. von Grafenstein, U. Griebner, and mel, J. Thøgersen, S. Techert, S. Toleikis, R. Treusch, S. T. Elsaesser; Generation of millijoule few-cycle pulses Trippel, A. Ulmer, C. Vallance, J. Wiese, P. Johnsson, J. at 5 μm by indirect spectral shaping of the idler in an Küpper, A. Rudenko, A. Rouzée, H. Stapelfeldt, D. Rolles, optical parametric chirped pulse amplifier; J. Opt. Soc.

and R. Boll; Photodissociation of aligned CH3I and C6H3F2I Am. B 35 (2018) C18-C24 molecules probed with time-resolved Coulomb explosion imaging by site-selective extreme ultraviolet ionization; BGM18: W. Becker, S. P. Goreslavski, D. B. Milošević, Struct. Dyn. 5 (2018) 014301/1-13 and G. G. Paulus; The plateau in above-threshold ionization: the keystone of rescattering physics, (Topical BBG18: J. Banerjee, S. Behnle, M. C. E. Galbraith, V. Set- Review); J. Phys. B 51 (2018) 162002/1-16 tels, B. Engels, R. Tonner, and R. F. Fink; Comparison of the periodic slab approach with the finite cluster descrip- BKl18: W. Becker and M. Kleber; Quantum sources in ex- tion of metal-organic interfaces at the example of PTCDA ternal fields; Phys. Scripta; https://doi.org/10.1088/1402- on Ag(110); J. Comput. Chem. 39 (2018) 844-852 4896/aaecae (2018) 1-24

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3+ terization and laser operation of Ho in “mixed” (Lu,Sc)2O3 ser passively Q-switched by single-walled carbon nano- ceramics; J. Lumin. 203 (2018) 145-151 tubes; Opt. Express; 26 (2018) 4961-4966

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ond-laser-written Tm:KLu(WO4)2 waveguide lasers by

JZA18: Á. Jiménez-Galán, N. Zhavoronkov, D. Ayuso, graphene and MoS2 saturable absorbers; SPIE Proc. F. Morales, S. Patchkovskii, M. Schloz, E. Pisanty, O. 10511 (2018) 105110A/1-6 Smirnova, and M. Ivanov; Control of attosecond light polarization in two-color bicircular fields; Phys. Rev. A 97 KPG18: D. Koulentianos, R. Püttner, G. Goldsztejn, T. (2018) 023409/1-14 Marchenko, O. Travnikova, L. Journel, R. Guillemin, D. Céolin, M. Novella Piancastelli, M. Simon, and R. Feif- KAB18: M. Kübel, M. Arbeiter, C. Burger, N. G. Kling, T. el; KL double core hole pre-edge states of HCl; Phys. Pischke, R. Moshammer, T. Fennel, M. F. Kling, and B. Chem. Chem. Phys. 20 (2018) 2724-2730 Bergues; Phase- and intensity-resolved measurements of above threshold ionization by few-cycle pulses; J. KSm18a: J. Kaushal and O. Smirnova; Looking inside Phys. B 51 (2018) 134007/1-8 the tunnelling barrier: I. Strong field ionisation from orbitals with high angular momentum in circularly polarised KDF18: A. Kundu, F. Dahms, B. P. Fingerhut, E. T. J. fields; J. Phys. B51 (2018) 174001/1-16 Nibbering, E. Pines, and T. Elsaesser; Ultrafast vibrational relaxation and energy dissipation of hydrated ex- KSm18b: J. Kaushal and O. Smirnova; Looking in- cess protons in polar solvents; Chem. Phys. Lett. 713 side the tunnelling barrier: II. Co- and counter-rotating (2018) 111-116 electrons at the ‘tunnelling exit’; J. Phys. B 51 (2018) 174002/1-15 KGE18a: M. Kubin, M. Guo, M. Ekimova, M. L. Baker, T. Kroll, E. Källman, J. Kern, V. K. Yachandra, J. Yano, KSm18c: J. Kaushal and O. Smirnova; Looking inside E. T. J. Nibbering, M. Lundberg, and P. Wernet; Direct the tunnelling barrier: III. Spin polarisation in strong field determination of absolute absorption cross sections at ionisation from orbitals with high angular momentum; J. the L-edge of dilute Mn complexes in solution using a Phys. B 51 (2018) 174003/1-12 transmission flatjet; Inorg. Chem.57 (2018) 5449-5462 KUO18: K. Kato, N. Umemura, T. Okamoto, and V. KGE18b: M. Kubin, M. Guo, M. Ekimova, E. Källman, Petrov; Upconversion of the mid-IR pulses to the near-

J. Kern, V. K. Yachandra, J. Yano, E. T. J. Nibbering, M. IR in LiGaS2; SPIE Proc. 10516 (2018) 105161D/1-6 Lundberg, and P. Wernet; Cr L-edge X-ray absorption

III spectroscopy of Cr (acac)3 in solution with measured KWD18: S. Kovalev, Z. Wang, J.-C. Deinert, N. Awari, and calculated absolute absorption cross sections; J. M. Chen, B. Green, S. Germanskiy, T. V. A. G. de Ol- Phys. Chem. B 122 (2018) 7375–7384 iveira, S. Lee, A. Deac, D. Turchinovich, N. Stojanovic, S. Eisebitt, I. Radu, S. Bonetti, T. Kampfrath, and M. KLR18a: E. Kifle, P. Loiko, J. R. Vázquez de Aldana, Gensch; Selective THz control of magnetic order: new A. Ródenas, S. Y. Choi, J. E. Bae, F. Rotermund, V. opportunities from superradiant undulator sources; J. Zakharov, A. Veniaminov, M. Aguiló, F. Díaz, U. Grieb- Phys. D 51 (2018) 114007/1-8 ner, V. Petrov, and X. Mateos; Passively Q-switched femtosecond-laser-written thulium wave guide laser KWF18: F. Krecinic, P. Wopperer, B. Frusteri, F. Brauße, based on evanescent field interaction with carbon nano- J. Brisset, U. de Giovannini, A. Rubio, A. Rouzée, and tubes; Photonics Res. 6 (2018) 971-980 M. J. J. Vrakking; Multiple-orbital effects in laser-induced electron diffraction of aligned molecules; Phys. KLR18b: E. Kifle, P. Loiko, C. Romero, J. R. Vázquez de Rev. A 98 (2018) 041401/1-5 Aldana, A. Ródenas, V. Jambunathan, V. Zakahrov, A. Veniamino, A. Lucianetti, T. Mocek, M. Aguiló, F. Díaz, LAK18: Z. Lécz, A. Andreev, I. Konoplev, A. Seryi, and U. Griebner, V. Petrov, and X. Mateos; Fs-laser-written J. Smith; Trains of electron micro-bunches in plasma erbium-doped double tungstate waveguide laser; Opt. wake-field acceleration; Plasma Phys. Control. Fusion Express 26 (2018) 30826-30836 60 (2018) 075012/1-9

KMB18a: K. Kato, K. Miyata, V. V. Badikov, and V. LAn18a: Z. Lécz and A. Andreev; Enhancement of high

Petrov; Thermo-optic dispersion formula for BaGa4Se7; harmonic generation by multiple reflection of ultrashort Appl. Opt. 57 (2018) 2935-2938 pulses; J. Opt. Soc. Am. B 35 (2018) A49-A55

KMB18b: K. Kato, K. Miyata, V. V. Badikov, and V. LAn18b: Z. Lécz and A. Andreev; Laser-induced ex-

Petrov; Phase-matching properties of BaGa2GeSe6 for treme magnetic field in nanorod targets; New J. Phys. three-wave interactions in the 0.778–10.5910 μm spec- 20 (2018) 033010/1-8 tral range; Appl. Opt. 57 (2018) 7440-7443

103 LBS18a: P. Loiko, J. Bogusławski, J. M. Serres, E. Ki- LSS18: P. Loiko, J. M. Serres, S. S. Delekta, E. Kifle, J. fle, M. Kowalczyk, X. Mateos, J. Sotor, R. Zybała, K. Bogusławski, M. Kowalczyk, J. Sotor, M. Aguiló, F. Díaz, Mars, A. Mikuła, M. Aguiló, F. Díaz, U. Griebner, and U. Griebner, V. Petrov, S. Popov, J. Li, X. Mateos, and

V. Petrov; Tm:GdVO4 microchip laser Q-switched by a M. Östling; Inkjet-printing of graphene saturable absorb-

Sb2Te 3 topological insulator; SPIE Proc. 10511 (2018) ers for ~2 µm bulk and waveguide lasers; Opt. Mater. 105110B/1-7 Express 8 (2018) 2803-2814

LBS18b: P. Loiko, T. Bora, J. M. Serres, H. Yu, M. Agu- LST18: Q. Liu, L. Seiffert, A. Trabattoni, M. C. Castrovilli, iló, F. Díaz, U. Griebner, V. Petrov, X. Mateos, and J. M. Galli, P. Rupp, F. Frassetto, L. Poletto, M. Nisoli, E. Dutta; Oriented zinc oxide nanorods: A novel saturable Rühl, F. Krausz, T. Fennel, S. Zherebtsov, F. Calegari, absorber for lasers in the near-infrared; Beilstein J. Nan- and M. F. Kling; Attosecond streaking metrology with otechnol. 9 (2018) 2730–2740 isolated nanotargets; J. Opt. 20 (2018) 024002/1-13

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and V. Petrov; Sb2Te 3 thin film for the passive Q-switch- Proc. 10549 (2018) 105490F/1-7

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Kato; 90° phase-matched Hg0.35Cd0.65Ga2S4 optical parametric oscillator pumped by a Nd:YAG laser; SPIE Proc. YMK18: F. Yesudas, M. Mero, J. Kneipp, and Z. Heiner; 10516 (2018) 1051619/1-6 Vibrational sum-frequency generation spectroscopy of lipid bilayers at repetition rates up to 100 kHz; J. Chem. VCP18: J. Vos, L. Cattaneo, S. Patchkovskii, T. Zim- Phys. 148 (2018) 104702/1-8 mermann, C. Cirelli, M. Lucchini, A. Kheifets, A. S. Landsman, and U. Keller; Orientation-dependent stereo YUG18: L. Young, K. Ueda, M. Gühr, P. H. Bucksbaum, Wigner time delay and electron localization in a small M. Simon, S. Mukamel, N. Rohringer, K. C. Prince, C. molecule; Science 360 (2018) 1326-1330 Masciovecchio, M. Meyer, A. Rudenko, D. Rolles, C. Bostedt, M. Fuchs, D. A. Reis, R. Santra, H. Kapteyn, VGM18: L. Vidas, C. M. Günther, T. A. Miller, B. Pfau, D. M. Murnane, H. Ibrahim, F. Légaré, M. J. J. Vrakking, Perez-Salinas, E. Martínez, M. Schneider, E. Guehrs, P. M. Isinger, D. Kroon, M. Gisselbrecht, A. L’Huillier, H. Gargiani, M. Valvidares, R. E. Marvel, K. A. Hallman, R. J. Wörner, and S. R. Leone; Roadmap of ultrafast x-ray F. Haglund, S. Eisebitt, and S. Wall; Imaging nanometer atomic and molecular physics; J. Phys. B 51 (2018) phase coexistence at defects during the insulator−metal 032003/1-45 phase transformation in VO2 thin films by resonant soft X‑ray holography; Nano Lett. 18 (2018) 3449-3453 ZFR18: C. Zhang, T. Feng, N. Raabe, and H. Rottke; Strong-field ionization of xenon dimers: The effect of VHH18: P. Varytis, D.-N. Huynh, W. Hartmann, W. Per- two-equivalent-center interference and of driving ionic nice, and K. Busch; Design study of random spectrome- transitions; Phys. Rev. A 97 (2018) 023417/1-11 ters for applications at optical frequencies; Opt. Lett. 43 (2018) 3180/1-4

107 ZGJ18: M. Zürch, A. Guggenmos, R. Jung, J. Rothhardt, EHB: M. Ekimova, F. Hoffmann, G. Bekçioğlu-Neff, A. C. Späth, J. Tümmler, S. Demmler, S. Hädrich, J. Limp- Rafferty, E. T. J. Nibbering, and D. Sebastiani; Ultrafast ert, A. Tünnermann, U. Kleineberg, H. Stiel, and C. Spiel- proton transport in water-methanol mixtures; in Ultrafast mann; Coherent diffraction imaging with tabletop XUV Phenomena XXI sources; in X-Ray Lasers 2016, Proceedings of the 15th International Conference on X-Ray Lasers, T. Kawachi et ERW: T. Elsaesser, K. Reimann, and M. Woerner, Con- al. eds. (Springer, Heidelberg, 2018) 231-241 cepts and applicatons of nonlinear terahertz spectroscopy, Morgan & Claypool Publishers, San Rafael, CA, USA) ZLM18: X. Zhang, P. Loiko, X. Mateos, J. M. Serres, J. Ren, J. Guo, R. Cheng, C. Gao, Q. Dong, V. Jambuna- FBS: B. P. Fingerhut, E. M. Bruening, J. Schauss, T. Sie- than, A. Lucianetti, T. Mocek, E. Vilejshikova, U. Grieb- bert, and T. Elsaesser; Interactions of RNA and water ner, V. Petrov, Z. Wang, S. Guo, X. Xu, M. Aguiló, and probed by 2D-IR spectroscopy; in Ultrafast Phenomena F. Díaz; Crystal growth, low-temperature spectroscopy XXI

and multi-watt laser operation of Yb:Ca3NbGa3Si2O14; J. Lumin. 197 (2018) 90-97 FRW: G. Folpini, K. Reimann, M. Woerner, L. von Grafenstein, M. Bock, U. Griebner, and T. Elsaesser; ZLS18: X. Zhang, P. Loiko, J. M. Serres, V. Jambuna- Millijoule few-cycle 5 μm source at 1 kHz repetition rate than, Z. Wang, S. Guo, A. Yasukevich, A. Lucianetti, T. for generating broadband pulses from the mid- to far-in- Mocek, U. Griebner, V. Petrov, X. Xu, M. Aguiló, F. Díaz, frared; in Ultrafast Phenomena XXI and X. Mateos; Passive Q switching of Yb:CNGS lasers by Cr4+:YAG and V3+:YAG saturable absorbers; Appl. Opt. HHH: C. Hauf, A.-A. Hernandez Salvador, M. Holtz, M. 57 (2018) 8236-8241 Woerner, and T. Elsaesser; Phonon driven charge dynamics in polycrystalline acetylsalicylic acid mapped by ZMK18: H. Zimmermann, S. Meise, A. Khujakulov, A. ultrafast x-ray diffraction; Struct. Dyn. Magaña, A. Saenz, and U. Eichmann; Limit on excitation and stabilization of atoms in intense optical laser fields; KCB: J. W. Kim, S. Y. Choi, J. E. Bae, M. H. Kim, Y. Phys. Rev. Lett. 120 (2018) 123202/1-6 U. Jeong, E. Kifle, X. Mateos, M. Aguiló, F. Díaz, U. Griebner, V. Petrov, G.-H. Kim, and F. Rotermund; Com- ZSL18: L. Zhang, S. Sun, Z. Lin, H. Lin, G. Zhang, X. parative study of Yb:KYW planar waveguide lasers Mateos, J. M. Serres, M. Aguiló, F. Díaz, P. Loiko, Y. Q-switched by direct- and evanescent-field interaction Wang, U. Griebner, V. Petrov, E. Vilejshikova, and W. with carbon nanotubes; Opt. Express Chen; Crystal growth, spectroscopy and first laser oper-

ation of a novel disordered tetragonal Tm:Na2La4(WO4)7 KEG: C. Kleine, M. Ekimova, G. Goldsztejn, S. Raabe, tungstate crystal; J. Lumin. 203 (2018) 676-682 C. Strüber, J. Ludwig, S. Yarlagadda, S. Eisebitt, M. J. J. Vrakking, T. Elsaesser, E. T. J. Nibbering, and A. ZWZ18: Y. Zhao, Y. Wang, X. Zhang, X. Mateos, Z. Pan, Rouzée; Soft X-ray absorption spectroscopy of aque- P. Loiko, W. Zhou, X. Xu, J. Xu, D. Shen, S. Suomalain- ous solutions using a table-top femtosecond soft X-ray en, A. Härkönen, M. Guina, U. Griebner, and V. Petrov; source; J. Phys. Chem. Lett.

87 fs mode-locked Tm,Ho:CaYAlO4 laser at ~2043 nm; Opt. Lett. 43 (2018) 915-918 KUI: K. Kato, N. Umemura, L. Isaenko, S. Lobanov, V. Vedenyapin, K. Miyata, and V. Petrov, Thermo-optic dis-

ZYC18: B. Zhao, Y. Ye, J. Chen, H. Lin, G. Zhang, X. Ma- persion formula for LiGaS2, Appl. Opt. teos, J. M. Serres, M. Aguiló, F. Díaz, P. Loiko, U. Grieb- ner, V. Petrov, and W. Chen; Growth, spectroscopy, and KZM: M. Kowalczyk, X. Zhang, X. Mateos, S. Guo, Z.

laser operation of “mixed” vanadate crystals Yb:Lu1-x-yYx- Wang, X. Xu, P. Loiko, F. Rotermund, J. Sotor, U. Grieb-

LayVO4; Opt. Mater. Express 8 (2018) 493-502 ner, V. Petrov, Graphene and SESAM mode-locked Yb:CNGS lasers with self-frequency doubling properties, Opt. Express

in press LTBa: M. Liebmann, A. Treffer, M. Bock, T. Seiler, J. Jahns, T. Elsaesser, and R. Grunwald; Spectral me- DKP: F. Dahms, A. Kundu, E. Pines, B. P. Fingerhut, E. ta-moments reveal hidden signatures of vortex pulses; T. J. Nibbering, and T. Elsaesser; Ultrafast dynamics of in Ultrafast Phenomena XXI

hydrated excess protons in CH3CN:H2O mixtures; in Ul- trafast Phenomena XXI LTBb: M. Liebmann, A. Treffer, M. Bock, T. Seiler, J. Jahns, T. Elsaesser, and R. Grunwald; Self-imaging of DRW: L. Drescher, G. Reitsma, T. Witting, S. Patch- tailored vortex pulse arrays and spectral Gouy rotation kovskii, J. Mikosch, and M. J. J. Vrakking; State-resolved echoes; Opt. Lett. probing of attosecond timescale molecular dipoles; J. Phys. Chem. Lett. LTF: R. Liao, H. Tian, T. Feng, Y. Song, M. Hu, and G. Steinmeyer; Active f-to-2f interferometer for record-low EFS: T. Elsaesser, G. Folpini, C. Somma, K. Reimann, jitter carrier-envelope phase locking; Opt. Lett. M. Holtz, A.-A. Hernandez Salvador, and M. Woerner; Soft-mode driven dynamics in ferroelectrics - new insight Mil: D. B. Milošević; Quantum-orbit analysis of high-or- from ultrafast terahertz and x-ray experiments; in Ultra- der harmonic generation by bicircular field; J. Mod. Opt. fast Phenomena XXI

108 RFi: M. Richter and B. P. Fingerhut; Electron transfer EWo: T. Elsaesser and M. Woerner; Femtosecond x-ray pathways and dynamics in drosophila cryptochrome - the diffraction: Nuclear motions and charge dynamics; in role of protein electrostatics; in Ultrafast Phenomena XXI Dynamic Structural Science: Monitoring Chemical and Biological Processes Across Time Domains (Wiley Pub- RFi/a: M. Richter et al.; Faraday Discuss. (2019) DOI: lishing) 10.1039/C8FD00189H HHL: S. L. Hu, X. L. Hao, H. Lu, T. X. Yang, H. F. Xu, M. SBL: M. Schnürer, J. Braenzel, A. Lübcke, and A. A. X. Jin, D. J. Ding, Q. G. Li, W. D. Li, M. Q. Liu, W. Beck- Andreev; Parametric study of cycle modulation in laser er, and J. Chen; Quantum dynamics of atomic Rydberg driven ion beams and acceleration field retrieval at fem- excitation in an intense laser field; Phys. Rev. Lett. tosecond time scale; Phys. Rev. Accel. Beams KRM: E. T. Karamatskos, S. Raabe, T. Mullins, A. Tra- SBSa: F. Schell, T. Bredtmann, C. P. Schulz, M. J. J. battoni, P. Stammer, G. Goldsztejn, R. R. Johansen, K. Vrakking, S. Patchkovskii, and J. Mikosch; Separation Długołecki, H. Stapelfeldt, M. J. J. Vrakking, S. Trippel, of strong-field ionization continua in laser-driven electron A. Rouzée, and J. Küpper; Molecular movie of ultrafast rescattering in the molecular frame; Proceedings in Atto06 coherent rotational dynamics; Nat. Commun. Conference, Springer Proceedings in Physics Series KWH: R. Kernke, H. Wang, J. Hong, F. Yue, J. Chu, and SDF: J. Schauss, F. Dahms, B. P. Fingerhut, and T. El- J. W. Tomm; Origin and applications of yellow emissions saesser; Phosphate–magnesium ion interactions in wa- from (In,Ga,Al)N based 450 nm emitting diode lasers; ter probed by ultrafast two-dimensional infrared spec- Opt. Lett. troscopy; J. Phys. Chem. Lett. LBD: A. Lübcke, J. Braenzel, A. Dehlinger, M. Schnürer, Ste: G. Steinmeyer; Megafilaments in the mid-infrared; H. Stiel, P. Guttmann, S. Rehbein, G. Schneider, S. Wer- Nat. Photonics ner, R. Kemmler, S. Ritter, M. Raugust, T. Wende, M. Behrendt, and M. Regehly; Soft X-ray nanoscale imaging TOV: A.Tajalli, M. Ouillé, A. Vernier, F. Böhle, E. Esco- using a superresolution CCD camera; Rev. Sci. Instrum. to, S. Kleinert, R. Romero, J. Csontos, U. Morgner, G. Steinmeyer, H. M. Crespo, R. L. Martens, and T. Nagy; LTBc: M. Liebmann, A. Treffer, M. Bock, T. Seiler, J. Propagation effects in the characterization of 1.5-cy- Jahns, T. Elsaesser, and R. Grunwald; Spectral self-im- cle pulses by XPW dispersion scan; IEEE J. Sel. Top. aging and Gouy rotation echoes of propagating vortex Quant. Electron. pulse arrays; SPIE Proc.

WSRa: M. Woerner, C. Somma, K. Reimann, T. El- MBe: D. B. Milosevic and W. Becker; Atom-Volkov saesser, I. Brener, J. L. Reno, Y. Yang, and P. Q. Liu; strong-field approximation for above-threshold ioniza- Terahertz driven amplification of coherent optical pho- tion; Phys. Rev. A nons in GaAs coupled to metallic dog-bone resonators; in Ultrafast Phenomena XXI MTR: F. Mahler, J. W. Tomm, K. Reimann, M. Woerner, V. Hoffmann, C. Netzel, M. Weyers, and T. Elsaesser; ZWC: Y. Zhao, Y. Wang, W. Chen, Z. Pan, L. Wang, X. Time-resolved photoluminescence from n-doped GaN/

Dai, H. Yuan, Y. Zhang, H. Cai, J. E. Bae, S. Y. Choi, F. Al0.18Ga0.82N short-period superlattices probes carrier ki- Rotermund, P. Loiko, J. M. Serres, X. Mateos, W. Zhou, netics and long-term structural stability; J. Appl. Phys. D. Shen, U. Griebner, and V. Petrov; 67-fs pulse generation from a mode-locked Tm,Ho:CLNGG laser at 2083 NAD: O. Neufeld, D. Ayuso, P. Decleva, M. Ivanov, O. nm; Opt. Express Smirnova, and O. Cohen; Ultra-sensitive chiral spectroscopy by dynamical symmetry breaking in high harmonic generation; Phys. Rev. X

Submitted NMS: L. Nahon, Y. Mairesse, and O. Smirnova; Circu- lar dichroism in photoemission of chiral molecules: from AHH: M. Aeschlimann, M. Hofherr, S. Häuser, P. Teng- static to time-resolved in roadmap on photonic, electron- din, S. Sakshath, H. T. Nembach, S. T. Weber, J. M. ic and atomic collision physics I. Light-matter interac- Shaw, T. J. Silva, H. C. Kapteyn, M. Cinchetti, B. Reth- tion; J. Phys. B feld, M. M. Murnane, D. Steil, B. Stadtmüller, S. Sharma, and S. Mathias; Coherent ultrafast spin transfer in ferro- OSm/a: A. F. Ordonez and O. Smirnova; Propensity magnetic alloys; Science rules in photoelectron circular dichroism in chiral molecules I: Chiral hydrogen; Phys. Rev. A ASM: M. Anikeeva, T. Schulz, F. Mahler, J. W. Tomm, L. Lymperakis, C. Cheze, R. Calarco, J. Neugebauer, and OSm/b: A. F. Ordonez and O. Smirnova; Propensity M. Albrecht; Recombination in InGaN quantum struc- rules in photoelectron circular dichroism in chiral mole- tures: Role of hole localization; Phys. Rev. B cules II: General picture; Phys. Rev. A

CBE: J. Chen, U. Bovensiepen, A. Eschenlohr, T. OSM: T. Oelze, B. Schuette, J. P. Muller, M. Wieland, U. Müller, P. Elliott, E. K. U. Gross, J. K. Dewhurst, and Fruhling, M. Frescher, T. Golz, A. Al-Shemmary, N. Sto- S. Sharma; Competing spin transfer and dissipation janovic, and M. Krikunova; Thz-streaking delay maps ul- at Co/Cu(001) interfaces on femtosecond timescales; trafast ionization of atoms and clusters; Phys. Rev. Lett. Phys. Rev. Lett.

109 RFi/b: M. Richter and B. P. Fingerhut; Coupled excitation Doe18: T. Doerries; Analyse von Röntgenstreubildern energy and charge transfer dynamics in reaction centre einzelner Xenoncluster mit Mie-Simulationen (Supervi- inspired model systems; Faraday Discuss. sor: D. Rupp and T. Möller), Technische Universität Berlin

SGO: F. Siegrist, J. A. Gessner, M. Ossiander, C. Denk- Kar18: A. Karamatskos; High harmonic generation to- er, Y.-P. Chang, M. C. Schroeder, A. Guggenmos, Y. Cui, wards the water window (Supervisor: S. Eisebitt and A. J. Walowski, U. Martens, J. K. Dewhurst, U. Kleineberg, Rouzée), Technische Universität Berlin M. Muenzenberg, S. Sharma, and M. Schultze; Peta- hertz spintronics; Nat. Phys. Klo18: C. Klose; Erzeugung und Manipulation von mag- netischen Bubble-Domänen (Supervisor: S. Eisebitt), Smi: O. Smirnova; Controlling, shaping and imaging Technische Universität Berlin quantum matter with intense light, in viewpoint on attosecond and FEL science; Nat. Rev. Phys. Loe18: L. Loechner; Erzeugung und Kompression von UV-Lichtpulsen durch Methoden der nichtlinearen Optik SMS: M. P. Schneider, C. Martens, T. Sproll, and K. Bus- (Supervisor: M. J. J. Vrakking and F. Franke), Freie Uni- ch; Decay properties of an atom coupled to a disordered versität Berlin waveguide; J. Opt. Soc. Am. B Men18: T. Menz; Untersuchung der Ionisationsdynamik SPG: P. Satapathy, A. Pfuch, R. Grunwald, and S. K. von XeKr-Mischclustern in intensiven Laserpulsen (Su- Das; Enhancement of photocatalytic activity by femtosec- pervisor: D. Rupp and T. Möller), Technische Universität ond-laser induced periodic surface structures; Catalysts Berlin

TKA: J. W. Tomm, R. Kernke, M. Ali, B. Stojetz, A. Lell, and Sta18: P. M. Stammer; Attosecond electron dynmamics H. König; Visible and near-infrared emission images of in intense bicircular fields (Supervisor: O. Smirnova and (In,Ga,Al)N-based 450 nm emitting diode laser; SPIE Proc. F. Morales), Technische Universität Berlin

WES: C.-Y. Wang, P. Elliott, S. Sharma, and J. K. De- Sto18: F. Stolberg; Aufbau einer durchstimmbaren whurst; Real time scissor correction in TD-DFT; J. Pump-Strecke für Labor-NEXAFS Untersuchungen (Su- Phys.-Condens. Mat. pervisor: B. Kanngießer and H. Stiel), Technische Uni- versität Berlin WFG: D. Weckbecker, M. Fleischmann, R. Gupta, W. Landgraf, S. Leitherer, O. Pankratov, S. Sharma, V. Med- ed, and S. Shallcross; Moiré ordered current loops in the graphene twist bilayer; Phys. Rev. Lett. Master theses

WGR: D. Weckbecker, R. Gupta, F. Rost, S. Sharma, Hec18: L. Hecht; Zweifarben-Streubildaufnahme von and S. Shallcross; Dislocation and node states in bilayer Helium-Nanotröpfchen - Planung, Durchführung und graphene systems; Nano Lett. erste Ergebnisse (Supervisor: D. Rupp and T. Möller), Technische Universität Berlin WSK: F. Willems, S. Sharma, C. von Korff Schmising, J. K. Dewhurst, L. Salemi, D. Schick, P. Hessing, C. Hei18: A. Heilrath; Ultrafast ionization dynamics of meth- Strüber, W. D. Engel, and S. Eisebitt; Magneto-optical ane clusters in XUV double pulses (Supervisor: D. Rupp functions at the 3p resonances of Fe, Co, and Ni: Ab-ini- and T. Möller), Technische Universität Berlin tio description and experiment; Phys. Rev. Lett. Jor18: J. Jordan; Untersuchung von lichtinduzierter Dy- WSRb: M. Woerner, C. Somma, K. Reimann, T. Elsaess- namik in Metallclustern mittels Röntgenbeugung (Su- er, P. Q. Liu, Y. Yang, J. L. Reno, and I. Brener; Terahertz pervisor: D. Rupp and T. Möller), Technische Universität driven amplification of coherent optical phonons in GaAs Berlin coupled to a metasurface; Phys. Rev. Lett. Kho18: S. Kholaif; Magneto-optical imaging of all-optical ZLF: C. Zhang, J. Lu, T. Feng, and H. Rottke; Proton switching with femtoseconds temporal and micrometer transfer dynamics following strong-field ionization of the spatial resolutions (Supervisor: S. Eisebitt and C. Spiel- water dimer; Phys. Rev. A mann), Technische Universität Berlin und Abbe School of Photonics, Friedrich-Schiller-Universität Jena

Kub18: T. Kubail Kalousdian; Generation and character- Bachelor, Master- and PhD theses ization of few-cycle DUV pulses using XPW generation D-scan (Supervisor: M. J. J. Vrakking and H.-J. Freund), Bachelor theses Freie Universität Berlin

Ber18: N. Bernhard; Spatial overlap in XUV/XUV pump- Sch18: J. Schauss; Ultrafast vibrational spectroscopy of probe experiments in the focus of CAMP at FLASH (Su- dimethylphosphate in an aqueous environment (Supervi- pervisor: D. Rupp and T. Möller), Technische Universität sor: T. Elsaesser), Humboldt-Universität zu Berlin Berlin

110 See18: F. Seel; Aufbau und Charakterisierung einer modularen Quelle für Edelgascluster (Supervisor: D. Rupp and T. Möller), Technische Universität Berlin

Wen18: S. Wenzel; Verstärkung Pikosekunden-Laser- quelle bei 2050 nm mittels Tm- und Ho-dotierten Wave- guide- und Faserverstärkern (Supervisor: T. Elsaesser), Humboldt-Universität zu Berlin

PhD theses

Dah18: F. Dahms; The hydrated excess proton studied by nonlinear time-resolved vibrational spectroscopy (Su- pervisor: T. Elsaesser), Humboldt-Universität zu Berlin

Gir18: A. Giree; High repetition rate optical parametric chirped-pulse amplification (Supervisor: M. J. J. Vrak- king and co-supervisor: Amplitude Technologies), Freie Universität Berlin

Gra18: L. von Grafenstein; Generation of intense few-cycle pulses in the mid-wave infrared (Supervisor: T. Elsaesser), Humboldt-Universität zu Berlin

Hol18: M. Holtz; Verschiebestrom induzierte Deforma- tionswellen in LiNbO3 gemessen mittels Schrotrausch- limitierter Femtosekunden-Röntgenbeugung (Super-visor: T. Elsaesser), Humboldt-Universität zu Berlin

Hum18: J. Hummert; Femtosecond XUV photoelectron spectroscopy of organic molecules in aqueous solution (Supervisor: M. J. J. Vrakking and K. Heyne), Freie Uni- versität Berlin

Hyy18: J. Hyyti; Ultrafast nonlinear nano-optics via collinear characterization of few-cycle pulses (Super-visor: G. Steinmeyer), Humboldt-Universität zu Berlin

Rei18: K. Reininger; Imaging strong-field induced molecular dynamics (Supervisor: J. Mikosch and M. J. J. Vrakking), Freie Universität Berlin

Sch18: M. Schneider; Non-linear X-ray diffraction from ferromagnetic thin-films (Supervisor: S. Eisebitt), Tech- nische Universität Berlin

111 Appendix 2 External Talks, Teaching

Invited talks at conferences L. Drescher together with G. Reitsma, T. Witting, S. A. A. Andreev and S. Ter-Avetisyan; 18th Int. Confer- Patchkovskii, J. Mikosch, and M. J. J. Vrakking; Gor- ence on Laser Optics, ICLO 2018 (St. Petersburg, Rus- don Research Conference, Photoionization and Photo- sia, 2018-06): Ultrashort PW laser plasma interaction detachment (Galveston, TX, USA, 2018-02): Molecular and ion acceleration light-induced couplings revealed by attosecond transient absorption spectroscopy A. A. Andreev; Workshop on Theory and Simulation of Photon-Matter Interaction (Szeged, Hungary, 2018-07): U. Eichmann; 27th Annual Int. Laser Physics Workshop Attosecond pulse generation and amplification in laser (LPHYS’18) (Nottingham, UK, 2018-07): Ultrafast atom- plasmas ic and molecular excitation in strong laser fields

A. A. Andreev; Int. Conference on Ultrafast Optical Sci- U. Eichmann; Thomas F. Gallagher retirement sympo- ence (UltrafastLight-2018) (Moscow, Russia, 2018-10): sium (University of Virginia, Charlottesville, USA, 2018- Efficient generation of attopulses at the interaction of in- 08): The exciting story of atoms and molecules in strong tense laser radiation with the shaped targets laser fields

U. Eichmann; Int. Workshop on Atomic Physics 2018 D. Ayuso; Quantum frontiers in molecular science (Tel- (Max Planck Institute for the Physics of Complex Sys- luride, USA, 2018-06): Chiral discrimination using high tems, Dresden, 2018-11): Channel closings in strong- harmonic generation: a giant macroscopic electric di- field excitation of atoms and molecules pole response S. Eisebitt; European XFEL SASE2 Workshop D. Ayuso; 256th ACS National Meeting & Exposition (Schenefeld, Germany, 2018-01): A split-and-delay line (Boston, USA, 2018-08): High harmonic generation in for MID@XFEL chiral media: from chiral discrimination to ultrafast imaging of molecular chirality S. Eisebitt; DPG-Frühjahrstagung der Sektion Konden- sierte Materie gemeinsam mit der EPS (Berlin, Germa- D. Ayuso; SILAP 2018 (Toronto, Canada, 2018-12): Ul- ny, 2018-03): A time-resolved view on magnetic domains trafast imaging of molecular chirality: achieving ultimate and spin textures by x-ray holography, Hauptvortrag efficiency in HHG S. Eisebitt; Synchrotron Radiation Instrumentation, SRI W. Becker; 27th Annual Int. Laser Physics Workshop 2018 (Taipei, Taiwan, 2018-06): Single shot fluence (LPHYS’18) (Nottingham, UK, 2018-07): Channel-clos- mapping of free electron laser pulses and recent ad- ing effects in multiphoton and tunneling ionization by a vances in X-ray holography bicircular laser field S. Eisebitt; Science@FELs 2018 (Stockholm, Sweden, K. Busch; Matheon-Workshop: 11th Annual Meeting 2018-06): How to know the x-ray fluence distribution on Photonic Devices (Berlin, Germany, 2018-02): At- your sample shot-by-shot om-surface interaction: theory and computations S. Eisebitt; 15th Epioptics School and 3rd Silicene K. Busch; XXVI Int. Workshop on Optical Wave & Wave- Workshop (Erice, Italy, 2018-07): Femtosecond X-ray guide Theory and Numerical Modelling (OWTNM 2018) sources: principles and applications (Bad Sassendorf, Germany, 2018-04): Atom-surface interaction: theory and computations S. Eisebitt; Bad Honnef Physics School on Physics with Free Electron Lasers (Bad Honnef, Germany, 2018-09): K. Busch; Workshop on Correlated Disorder, Hyperuni- X-ray holography and magnetism formity and Local Self-Uniformity (Guildford, UK, 2018- 06): Design of an integrated random spectrometer T. Elsaesser; XVII. DESY Research Course 2018 - Trends in Water Research (Hamburg, Germany, 2018-02): Ul- K. Busch; Workshop on synthetic non-hermitian photon- trafast hydration dynamics of protons and biomolecules ic structures: recent results and future challenges (Dres- mapped by two-dimensional infrared spectroscopy den, Germany, 2018-08): Quasi-normal-mode based quantization of dissipative and open systems T. Elsaesser; EOS Topical Meeting on Terahertz Sci- ence & Technology 2018 (Berlin, Germany, 2018-05): Nonlinear terahertz spectroscopy - basic concepts and applications in solid state physics (keynote talk)

112 T. Elsaesser; Int. School of Crystallography: Quantum F. J. Furch together with T. Witting, F. Schell, M. Os- Crystallography (Erice, Italy, 2018-06): Femtosecond olodkov, C. P. Schulz, and M. J. J. Vrakking; OSA Latin x-ray diffraction America Optics and Photonics Congress (Lima, Peru, 2018-11): Towards attosecond pump-probe coincidence T. Elsaesser; The 9th Int. Conference on Coherent Multi- spectroscopy with high acquisition rates dimensional Spectroscopy (CMDS) 2018 (Seoul, South Korea, 2018-06): Structure and dynamics of hydrated U. Griebner together with L. von Grafenstein, M. Bock, excess protons in polar solvents mapped by ultrafast and T. Elsaesser; Pacific Rim Laser Damage 2018 (Yo- 2D-IR sprectroscopy kohama, Japan, 2018-04): Generation of few-cycle milli-

joule pulses at 5 µm employing a ZnGeP2-based OPCPA T. Elsaesser; Workshop on Advances of Multidimen- pumped with GW peak power pulses at 2 µm sional Vibrational Spectroscopy in Water, Biology and Materials Science (Telluride, CO, USA, 2018-07): Ultra- U. Griebner together with L. von Grafenstein, M. Bock, fast hydration dynamics of protons and biomolecules and T. Elsaesser; 18th Int. Conference on Laser Optics mapped by 2D-IR spectroscopy 2018 (St. Petersburg, Russia, 2018-06): High energy kilohertz repetition rate laser system at 5 µm with multi- T. Elsaesser; Ultrafast Phenomena XXI (Hamburg, Ger- GW peak power many, 2018-07): Soft-mode driven dynamics in ferroelectrics - new insight from ultrafast terahertz and x-ray U. Griebner together with L. von Grafenstein, M. Bock, experiments D. Ueberschär, and T. Elsaesser; ALT18 - Advanced La- ser Technology (Tarragona, Spain, 2018-09): Few-cycle T. Elsaesser; Primary Processes of Matter (Chinese millijoule 5 µm optical parametric chirped-pulse amplifier Academy of Sciences, Bejiing, China, 2018-11): Charge at a 1 kHz repetition rate density and polarization dynamics - new insight from ultrafast terahertz and x-ray experiments A. Husakou together with M. Alharbi, M. Chafer, B. Debord, F. Gerome, and F. Benabid; Days on Diffraction T. Elsaesser; Int. Workshop on “Probing Biological Mat- (St. Petersburg, Russia, 2018-06): Coupled wave prop- ter with and without Labels” (Freie Universität Berlin, agation and nanotrap lattice in hollow fiber filled with Germany, 2018-11): Backbone vibrations of hydrated Raman-active gas DNA and RNA as noninvasive probes of ultrafast structural dynamics F. Intravaia; German-BGU (Ben Gurion University) Work- shop on Quantum Technology (Beer Sheva, Israel, 2018- T. Elsaesser; Int. Symposium on Ultrafast Science: From 12): Conservative and non-conservative dispersion forces the infrared to the X-rays (Lausanne, Switzerland, 2018- 11): Soft-mode driven dynamics in ferroelectrics - new M. Ivanov; Symposium on Recollision Physics 2018 insight from ultrafast terahertz and x-ray experiments (Montebello, Quebec, Canada, 2018-05): Strong field spectroscopy of electron dynamics: from laser filaments T. Fennel; QUTIF annual meeting 2018 (Hamburg, Ger- to strongly correlated solids many, 2018-02) M. Ivanov, CECAM School: New Computational Meth- T. Fennel; Theory Seminar, AG Berakdar (University ods for Attosecond Molecular Processes (Zaragoza, Halle, Germany, 2018-06) Spain, 2018-05): Analytical Strong Field Methods in In- tense Laser Fields T. Fennel; EUCALL workshop: Theory and simulation of photon-matter interaction (Szeged, Hungary, 2018-07) M. Ivanov; MURI Mid Infrared Annual Meeting 2018 (Ar- lington, USA, 2018-05): High harmonic spectroscopy of T. Fennel; 19th International symposium on small parti- phase transitions cles and inorganic clusters (Hangzhou, China, 2018-08) M. Ivanov; Gordon Research Conference on Multiphoton T. Fennel; International workshop attosecond physics at Processes (Smithfield, RI, USA, 2018-06): High harmon- the nanoscale (Daejon, South Korea, 2018-10) ic generation spectroscopy of phase transitions in solids

F. J. Furch together with T. Witting, F. Schell, P. Susn- M. Ivanov; Int. Workshop on Atomic Physics (Dresden, jar, F. Cavalcante, C. Menoni, C. P. Schulz, and M. J. J. Germany, 2018-11): Strong field physics in topological Vrakking; OSA High-brightness Sources and Light-driv- systems en Interactions Congress (Strasbourg, France, 2018- 03): Generation of high-order harmonics at 100 kHz for Á. Jiménez Galán together with F. Schell, T. Bredtmann, attosecond science experiments C.-P. Schulz, S. Patchkovskii, and M. J. J. Vrakking; QUTIF Workshop 2018 (Hamburg, Germany, 2018-02): F. J. Furch together with T. Witting, F. Schell, C. P. Control of attosecond light polarization in two color bi- Schulz, and M. J. J. Vrakking; IX Int. Conference for circular fields Professionals and Young Scientists - Low temperature physics (Kharkiv, Ukraine, 2018-06): Progress towards Á. Jiménez Galán; SILAP 2018 (Toronto, Canada, 2018- attosecond pump-probe spectroscopy with electron-ion 12): Topological strong field physics on sub-laser cycle coincidence detection timescale

113 Á. Jiménez Galán; XIX Int. Conference, Foundations & V. Petrov; CLEO Conference on Lasers and Electro-Op- Advances in Nonlinear Science and IV Int. Symposium tics (San Francisco, CA, USA, 2018-05): Progress in the Advances in Nonlinear Photonics (Minsk, Belarus, 2018- development of all-solid-state coherent sources in the 09): Generation and characterization of chiral attosec- mid-IR above 5 µm for surgical applications ond pulses using two-color tailored fields V. Petrov together with Y. Wang, Z. Pan, Y. Zhao, W. M. P. Kalashnikov; 18th Int. Conference on Laser Optics, Chen, M. Mero, F. Rotermund, P. Loiko, X. Mateos, X. ICLO 2018 (St. Petersburg, Russia, 2018-06): Future of Xu, J. Xu, H. Yu, H. Zhang, and U. Griebner; CLEO Pa- Ti:Sapphire lasers: combining high peak and average cific, Conference on Lasers and Electro-Optics CLEO/ power Pacific Rim’18 (Hong Kong, China, 2018-07):2D materials for mode-locking of bulk 2 micron lasers: alternatives O. Kornilov together with H. Hummert, G. Reitsma, to SESAMs N. Mayer, E. Ikonnikov, and M. Eckstein; DPG Früh- jahrstagung (Erlangen, Germany, 2018-03): Electronic V. Petrov together with P. Loiko, L. Zhang, H. Lin, G. structure and relaxation of solvated organic molecules Zhang, J. M. Serres, E. Kifle, Y. Wang, J. R. Vázquez studied by time-resolved photoelectron spectroscopy de Aldana, C. Romero, M. Aguiló, F. Díaz, U. Griebner, Z. Lin, W. Chen, and X. Mateos; The 26th Annual Inter- A. Mermillod-Blondin; Progress in Ultrafast Laser Mod- national Conference on Advanced Laser Technologies, ifications of Materials (Telluride, USA, 2018-06): Diag- ALT’18 (Tarragona, Spain, 2018-09): Monoclinic mono- nostics of laser-induced plasma formation in solid di- tungstates - novel efficient laser materials electrics V. Petrov; The 26th Annual Int. Conference on Advanced J. Mikosch together with F. Schell, T. Bredtmann, C. P. Laser Technologies, ALT’18 (Tarragona, Spain, 2018- Schulz, S. Patchkovskii, and M. J. J. Vrakking; QUTIF 09): Progress in the generation of ultrashort light pulses Workshop 2018 (Hamburg, Germany, 2018-02): Mo- in the 2-micron spectral range by passive mode-locking lecular orbital imprint in laser-driven electron recollision of Tm and Ho bulk solid-state lasers

J. Mikosch together with F. Schell, T. Bredtmann, C. P. B. Pfau; DESY Photon Science Users’ Meeting (Ham- Schulz, S. Patchkovskii, and M. J. J. Vrakking; DPG burg, Germany, 2018-01): Field-free deterministic ultra- Frühjahrstagung (Erlangen, Germany, 2018-03): Molec- fast creation of magnetic skyrmions by spin-orbit torques ular orbital imprint in laser-driven electron recollision B. Pfau; SPIE Optics and Photonics 2018 (San Diego, F. Morales together with M. Richter, O. Smirnova, and M. USA, CA, 2018-08): Field-free deterministic ultrafast Ivanov; XIX Int. Conference, Foundations & Advances in creation of magnetic skyrmions by spin–orbit torques Nonlinear Science and IV Int. Symposium Advances in Nonlinear Photonics (Minsk, Belarus, 2018-09): Optical K. Reimann together with K. Shinokita, M. Woerner, T. lasing during laser filamentation in the nitrogen mole- Elsaesser, R. Hey, and C. Flytzanis; 16th Int. Confer- cule: rovibrational inversion ence on Phonon Scattering in Condensed Matter (Pho- nons 2018) (Nanjing, China, 2018-05): Phonon amplifi- E. T. J. Nibbering together with F. Dahms, A. Kundu, M. cation in semiconductor nanostructures Ekimova, F. Hoffmann, G. Bekçioğlu-Neff, B. P. Finger- hut, D. Sebastiani, E. Pines, and T. Elsaesser; 256th H. Reiss; 10th Asian Symposium on Intense Laser ACS National Meeting & Exposition (Boston, MA, USA, Science (ASCILS10) (American University of Sharjah, 2018-08): Ultrafast mid-infrared spectroscopy of hy- Sharjah, UAE, 2018-03): Strong-field physics without the drated protons and proton transport in solvent mixtures dipole approximation

T. Noll; 12. Tagung Feinwerktechnische Konstruktion H. Reiss; 27th Annual Int. Laser Physics Workshop (Dresden, Germany, 2018-09): Konstruktionsprinzipien (LPHYS’18) (Nottingham, UK, 2018-07): Potentials are für ultrapräzise Positionierungen primary in electrodynamics and fields are secondary

S. Patchkovskii; Symposium on Recollision Physics H. Reiss; 27th Annual Int. Laser Physics Workshop 2018 (Montebello, Quebec, Canada, 2018-05): Three- (LPHYS’18) (Nottingham, UK, 2018-07): Pairs from the step factorization and essential molecular symmetries vacuum

A. Perez-Leija; Meeting of the Mexican Quantum Infor- M. Richter together with M. Ivanov; 49th Annual Meet- mation Division DICU 2018 (Guanajuato, Mexico, 2018- ing of the APS Division of Atomic, Molecular and Optical 09): On-chip laser-written photonic circuits for quantum Physics (Florida, FL, USA, 2018-05): Strong-field spec- application troscopy of electron dynamics: from laser filaments to strongly correlated solids V. Petrov together with X. Mateos, P. Loiko, S. Lam- rini, K. Scholle, P. Fuhrberg, S. Suomalainen, A. A. Rouzée; 9th Int. Meeting on Atomic and Molecular Härkönen, M. Guina, S. Vatnik, I. Vedin, M. Aguiló, F. Physics and Chemistry (Berlin, Germany, 2018-06): La- Díaz, Y. Wang, and U. Griebner; 2018 Pacific Rim Laser ser-based imaging of isolated molecules and nanoparti- Damage (Yokohama, Japan, 2018-04): Highly-efficient cles

Ho:KY(WO4)2 thin-disk lasers at 2.06 μm

114 D. Rupp together with N. Monserud, M. Sauppe, J. Zimmer- O. Smirnova; Symposium on Recollision Physics 2018 mann, K. Kolatzki, B. Schütte, M. J. J. Vrakking, T. Fennel, (Montebello, Quebec, Canada, 2018-05): On subtle dif- and A. Rouzée; DESY User Meeting (Hamburg, Germa- ference between left and right: From ultrafast dynamics ny, 2018-01): Coherent diffractive imaging of single helium to topology nanodroplets with a high harmonic generation source O. Smirnova; CECAM School: New Computational D. Rupp together with K. Kolatzki, M. Sauppe, B. Senfft- Methods for Attosecond Molecular Processes (Zarago- leben, J. Zimmermann, and T. Fennel; Science at FELs za, Spain, 2018-05): Analytical strong field methods 2018 (Stockholm, Sweden, 2018-06): Imaging FEL-induced dynamics in single nanoparticles O. Smirnova; Int. Symposium on Light Driven Dynamics (LiDy) (East China Normal University, Shanghai, China, M. Sauppe together with K. Kolatzki, N. Monserud, B. 2018-11): Locally chiral optical fields for controlling ultra- Senfftleben, J. Zimmermann, and D. Rupp; SNI 2018 fast chiral dynamics German Conference for Research with Synchrotron Radiation, Neutrons and Ion Beams at Large Facilities O. Smirnova; QUTIF-Young Researcher Meeting Quan- (München, Germany, 2018-09): X-ray movie camera: tum Dynamics in Tailored Intense Fields (Berlin, Ger- A novel approach for time-resolved single-particle im- many, 2018-12): Strong field ionization: ionization times aging and electron spin polarization

C. P. Schulz; Gordon Research Conference on Multi- G. Steinmeyer; SPIE Photonics West 2018 (San Fran- photon Processes (Smithfield, RI, USA, 2018-06): Mo- cisco, CA, USA, 2018-01): The role of intrapulse coher- lecular orbital imprint in laser-driven electron recollision ence for supercontinuum generation

C. P. Schulz; 27th Annual Int. Laser Physics Workshop G. Steinmeyer; AT-RASC 2018 (Maspalomas, Gran Ca- (LPHYS’18) (Nottingham, United Kingdom, 2018-07): naria, Spain, 2018-05): Optical rogue waves as an indi- Laser-driven electron rescattering in the molecular cator for the loss of intrapulse coherence frame: Separation of strong-field ionization continua G. Steinmeyer together with T. Feng, P. Rustige, and B. Schütte together with L. Drescher, O. Kornilov, T. N. Raabe; CLEO 2018 (San Jose, CA, USA, 2018-05): Witting, G. Reitsma, J. Mikosch, and M. J. J. Vrakking; Electric-field induced second-harmonic generation of DPG Frühjahrstagung (Erlangen, Germany, 2018-03): femtosecond laser pulses in atmospheric air Controlling the refraction of ultrashort XUV pulses G. Steinmeyer; COFIL 2018 (Geneva, Switzerland, B. Schütte together with L. Drescher, O. Kornilov, T. 2018-06): Intrapulse coherence of laser filaments Witting, N. Monserud, A. Rouzée, J. Mikosch, and M. J. J. Vrakking; 27th Annual Int. Laser Physics Workshop G. Steinmeyer; 27th Annual Int. Laser Physics Work- (LPHYS’18) (Nottingham, UK, 2018-07): Extreme-ultra- shop (LPHYS’18) (Nottingham, UK, 2018-07): Intra- violet refractive optics pulse coherence of laser filaments

B. Schütte; Int. Workshop on Atomic Physics (Dresden, H. Stiel; 16th ICXRL, Int. Conference on X-ray Lasers Germany, 2018-11): Control of XUV beam trajectories (Prague, Czech Republic, 2018-10): Soft X-ray near by atomic jets absorption edge spectroscopy in the water window and beyond in the lab S. Sharma; SPICE Workshop 2018: Ultrafast Spin- tronics: from Fundamentals to Technology (Johannes J. W. Tomm together with R. Kernke, A. Löffler, B. Sto- Gutenberg Universität Mainz, Germany, 2018-10): Ul- jetz, A. Lell, and H. König; SPIE Photonics West 2018 trafast optical switching by laser induced inter-site spin (San Francisco, CA, USA, 2018-01): Defect evolution transfer during catastrophic optical damage (COD) in 450-nm emitting InGaN/GaN diode lasers O. Smirnova; Gordon Research Conference ‘Photo- ionization & Photodetachment’ - From Attoseconds to J. W. Tomm; 2018 MRS Spring Meeting & Exhibit (Phoe- Nanoseconds: The Chemistry and Physics of Electrons, nix, AZ, USA, 2018-04): In situ analysis of diode lasers Atoms, Molecules, and Light (Galveston, TX, USA, and their degradation by using imaging techniques 2018-02): Chirality and stereochemistry (discussion leader) J. W. Tomm; 26th Int. Semiconductor Laser Conference - ISLC2018 (Santa Fe, NM, USA, 2018-09): Facet sta- O. Smirnova; PALM Int. School 2018, Attosecond Sci- bility of high-power GaN-based diode lasers ence: from ultrafast sources to applications (Gif-sur- Yvette, France, 2018-03): Strong field ionization: ioniza- J. W. Tomm together with F. Mahler; The 10th Int. Con- tion times and electron spin polarization ference on Photonics and Applications (Ha Long City, Vietnam, 2018-11): Spectroscopy of GaN-based super- O. Smirnova; Discussion workshop “Light field induced lattices dynamics in low dimensional systems” (Universität Duisburg-Essen, Germany, 2018-04): On subtle differ- M. J. J. Vrakking; ACS meeting (Boston, MA, USA, ence between left and right: inducing and probing ultra- 2018-08): The many benefits of high-harmonic radiation fast chiral dynamics

115 M. J. J. Vrakking; Symposium on Recollision Physics B. P. Fingerhut, Seminar Theoretische Chemie (Uni- 2018 (Montebello, Quebec, Canada, 2018-05): Imaging versität Potsdam, Germany, 2018-12): Non-equilibrium nuclear wave packets through laser-induced electron dynamics in the presence of a dissipative environment

diffraction in photoexcited I2 molecules - recent progress of the iterative quasi-adiabatic propa- gator path integral method M. J. J. Vrakking; Stereodynamics 2018 (Arosa, Swit- zerland, 2018-09): The many benefits of high-harmonic F. J. Furch, Seminar (Ruhr-Universität Bochum, Germa- radiation ny, 2018-06): Towards attosecond pump-probe spectroscopy at high repetition rates F. Willems; Transregio 227 Retreat (Halle, MLU, Germa- ny, 2018-06): Probing ultrafast magnetization dynamics F. J. Furch, Seminar (Pontificia Universidad Católica, with element-specificity using high harmonic light sources Santiago de Chile, Chile, 2018-08): Ultrashort pulses with high energy and high repetition rate. Applications in F. Willems; SPICE Workshop 2018: Ultrafast Spin- attosecond physics tronics: from Fundamentals to Technology (Johannes Gutenberg Universität Mainz, Germany, 2018-10): Mag- F. J. Furch, Seminar (Universidad de Concepción, Con- neto-optical constants and their transient changes in ul- cepción, Chile, 2018-08): Ultrashort pulses with high en- trafast XUV spectroscopy ergy and high repetition rate. Applications in Attosecond Physics M. Woerner; Discussion Workshop “Light field induced dynamics in low dimensional systems” (Universität F. J. Furch, Seminar (Universidad de Buenos Aires, Duisburg-Essen, Germany, 2018-04): Nonlinear soft- Buenos Aires, Argentina, 2018-08): Ultrashort pulses mode dynamics studied by 2D terahertz spectroscopy with high energy and high repetition rate. Applications in and femtosecond X-ray diffraction Attosecond Physics

F. J. Furch, Seminar (Mody University of Science and Techonology, Lankshmangahr, India, 2018-10): Explor- Invited external talks at seminars and col- ing ultrafast dynamics in atoms and molecules with pow- loquia erful laser sources

W. Becker, Atomic Molecular and Optical Seminar (Tex- F. J. Furch, Seminar (Masdar Institute of Science and as AM University, Department of Physics & Astronomy, Technology, Abu Dhabi, United Arab Emirates, 2018- USA, 2018-10): Circularly polarized high-order harmon- 10): Ultrashort laser pulses with high average power ics from tailored laser pulses and high repetition rate. Applications in atto-science and material processing K. Busch, Seminar (Bad Herrenalb, Germany, 2018-09): Atom-surface interaction: theory and computations K. Grundmann, Praxisseminar: Digitale Verwaltung in Hochschul- und Forschungseinrichtungen (InterCity Ho- S. Eisebitt, Seminar (Friedrich-Schiller-Universität, In- tel, Berlin Hauptbahnhof, Germany, 2018-06-22): Digi- stitut für Optik und Quantenelektronik, Jena, Germany, talisierung - Möglichkeiten und Herausforderungen für 2018-05): A time-resolved view on magnetic domains die Verwaltung am Max-Born-Institut and spin textures by x-ray holography O. Kornilov together with H. Hummert, G. Reitsma, N. S. Eisebitt, Physikalisches Kolloqium (Universität Kas- Mayer, E. Ikonnikov, and M. Eckstein; Fritz-Haber-In- Kassel, Germany, 2018-12): Tickling magnetization with stitut der Max-Planck-Gesellschaft (Berlin, Germany, electrons and light 2018-06): Electronic structure and relaxation of solvated organic molecules studied by time-resolved photoelec- T. Elsaesser, Young Leaders Programm 2018, Förder- tron spectroscopy kreis der Deutschen Industrie (Berlin, Germany, 2018- 08): Quantentechnologie – Wann kommt die nächste O. Kornilov; IRTG Int. Research Training Group semi- Revolution? nar (Freiburg, Germany 2018-07): Electronic structure and relaxation of solvated organic molecules studied by T. Elsaesser, Akademische Causerie, Berlin-Branden- time-resolved photoelectron burgische Akademie der Wissenschaften (Berlin, Ger- many, 2018-12): Wasser und Biomoleküle - schnelle E. T. J. Nibbering, Seminar (Max-Planck-Institut für Bewegungen und intensive Beziehungen Struktur und Dynamik der Materie, CFEL, Hamburg, Germany, 2018-10): Exploring and exploiting photoac- T. Elsaesser, Münchner Physik Kolloquium (Lud- ids to reveal ultrafast hydrogen bond and proton transfer wig-Maximilians-Universität München, Germany, 2018- dynamics in solution: how to move from the mid-IR to 12): Ions and biomolecules in water - ultrafast motions the soft-X-ray regime and electric interactions E. T. J. Nibbering, Seminar (École Normale Supérieure, B. P. Fingerhut, Kolloquium der Physikalischen Chemie Département de Chimie, Paris, France, 2018-11): Ex- (Ludwig-Maximilians-Universität München, Germany, ploring and exploiting photoacids to reveal ultrafast hy- 2018-11): Electron transfer pathways in drosophila cryp- drogen bond and proton transfer dynamics in solution: tochrome - the role of protein electrostatics how to move from the mid-IR to the soft-X-ray regime

116 V. Petrov, Seminar (Institute of Chemical Materials, C. von Korff Schmising; SCS Workshop European XFEL Chengdu, China 2018-10): Generation of ultrashort light „Digitale Agenda“ (DESY, Hamburg, Germany, 2018- pulses in the 2-micron spectral range by Tm and Ho bulk 02): User X-ray solid-state lasers C. von Korff Schmising, Seminar (Universität Duis- I. Radu, Seminar (Westfälische Wilhelms-Universität, burg-Essen, Germany, 2018-06): Probing ultrafast Physikalisches Institut, Münster, Germany, 2018-05): magnetization dynamics with element-specificity using When THz meets x-rays: an ultrafast view on magne- free-electron and high harmonic light sources tism C. von Korff Schmising; The International School on I. Radu, Seminar (PSI-Paul Scherrer Institute, Villingen XFEL - Science and Instrumentation (Gdansk, Poland, and ETH Zurich, Switzerland, 2018-11): When THz 2018-10): Imaging ultrafast magentization dynamics meets x-rays: an ultrafast view on magnetism M. Woerner, Seminar (Universität Erlangen, Germany, D. Rupp, ICTP Summer School on Synchrotron and 2018-02): Two-dimensional terahertz spectroscopy on Free-Electron-Laser Methods for Multidisciplinary Ap- crystalline solids plications (Trieste, Italy, 2018-05): Cluster imaging by coherent diffraction and novel instrumentation to do so

D. Rupp, MBI Technikerschulung (Erkner, Germany, Academic teaching 2018-10): Schnappschüsse von kurzlebigen Strukturen und ultraschnellen Dynamiken auf der Nanoskala A. A. Andreev, Vorlesung, 4 SWS (Universität Olden- burg/Emden, WS 2017/18 and SS 2018): Quantum op- D. Schick, Seminar (Jülich, Germany, 2018-10): Mag- tics & plasma physics; Laser-plasma physics and appli- netic and structural dynamics in antiferromagnetically cations coupled Fe/Cr superlattices A. A. Andreev, Vorlesung, 2 SWS (Universität Olden- S. Sharma, Tutorial (Freie Universität Berlin, Germany, burg, WS 2017/18): Laser Plasma Physics and Appli- 2018-10): ABC of DFT cations

O. Smirnova, Kolloquium (University of Rostock, Ger- A. A. Andreev, Vorlesung, 2 SWS (Universität Olden- many, 2018-05): On subtle difference between left and burg, WS 2017/18): Quantum Optics/Plasma Physics/ right: Inducing and probing ultrafast chiral dynamics Specialization Laser & Optics on request as Module Ad- vanced Physics II O. Smirnova, Student Invited Lecture (Princeton, NJ, USA, 2018-11): Locally chiral optical fields for controlling A. A. Andreev, together with H. J. Brückner, S. Koch, ultrafast chiral dynamics M. Schellenberg, B. Struve, U. Teubner, W. Neu, W. Garen, T. Schüning, S. Wild, J. Diekhoff, L. Jepsen, S. G. Steinmeyer, Antrittsvorlesung (Humboldt-Universität Tiedeken, V. Braun, and A. Hinrichs; Vorlesung, 2 SWS zu Berlin, Germany, 2018-01): Koheränz ultrakurzer (Universität Oldenburg/Emden, WS 2017/18): Laborato- Lichtpulse ry Project I

G. Steinmeyer, Laser Seminar (ETH Zurich, Switzerland, T. Bredtmann, together with M. Ivanov; Vorlesung, 2 2018-10): Carrier-envelope phase stabilization of mode- SWS (Humboldt-Universität zu Berlin, SS 2018): Nicht- locked lasers: towards zeptosecond timing control lineare Optik

G. Steinmeyer, Laser Seminar (Université Neuchâtel, T. Bredtmann, together with M. Ivanov; Übungen, 2 Switzerland, 2018-11): Carrier-envelope phase stabi- SWS (Humboldt-Universität zu Berlin, SS 2018): Nicht- lization of mode-locked lasers: towards zeptosecond lineare Optik timing control K. Busch and A. Perez-Leija, Vorlesung, 2 SWS (Hum- H. Stiel, Institutskolloquium (Institut für Optik und Quan- boldt-Universität zu Berlin, WS 2017/18): Diskrete tenelektronik FSU Jena, 2018-02): Soft X-ray absorp- Quantenoptik tion spectroscopy and imaging using laser based laboratory sources K. Busch together with A. Perez-Leija, D.-N. Huynh, and P. Varytis, Übungen, 2 SWS (Humboldt-Universität zu H. Stiel, Institutskolloquium (Warsaw, Poland, 2018-06): Berlin, WS 2017/18): Diskrete Quantenoptik NEXAFS spectroscopy in the lab K. Busch, Vorlesung, 2 SWS (Humboldt-Universität zu J. W. Tomm, Institute Colloquium (East China Normal Berlin, SS 2018): Computerorientierte Photonik University, Shanghai, China, 2018-10): GaN-based optoelectronics - from fundamentals to applications K. Busch together with D.-N. Huynh and T. Kiel; Übun- gen, 2 SWS (Humboldt-Universität zu Berlin, SS 2018): J. W. Tomm, Lecture (School of Information Science Computerorientierte Photonik Technology, East China Normal University, Shanghai, China, 2018-11): Introduction to semiconductor lasers

117 K. Busch together with A. Perez-Leija, Vorlesung, 2 SWS M. Ivanov, Vorlesung (Humboldt-Universität zu Berlin, (Humboldt-Universität zu Berlin, WS 2018/19): Diskrete WS 2018/19): Quantum dynamics in strong laser fields Quantenoptik M. Ivanov, Übungen (Humboldt-Universität zu Berlin, WS K. Busch together with A. Perez-Leija, and P. Varytis, 2018/19): Quantum dynamics in strong laser fields Übungen, 2 SWS (Humboldt-Universität zu Berlin, WS 2018/19): Diskrete Quantenoptik D. Rupp, Vorlesung, 2 SWS (Technische Universität Ber- K. Busch together with A. Perez-Leija, and P. Varytis, lin, SS 2018) Physik für Elektrotechnik Vorlesung, 2 SWS (Humboldt-Universität zu Berlin, WS 2018/19): Fundamentals of optical sciences O. Smirnova together with U. Woggon; Vorlesung und Übungen, 4 SWS (Technische Universität Berlin, WS K. Busch together with A. Perez-Leija, and P. Varytis, 2017/18): Höhere Optik I Übungen, 2 SWS (Humboldt-Universität zu Berlin, WS 2018/19): Fundamentals of optical sciences O. Smirnova together with U. Woggon; Vorlesung und Übungen, 4 SWS (Technische Universität Berlin, SS U. Eichmann together with O. Dopfer; Vorlesung und 2018): Höhere Optik II Übungen, 4 SWS (Technische Universität Berlin, WS 2017/18): Quantensysteme I G. Steinmeyer, Vorlesung, 4 SWS (Humboldt-Universität zu Berlin, WS 2018/19): Physik III Optik S. Eisebitt together with B. Kanngießer and T. Möller; Vorlesung und Übungen, 4 SWS (Technische Universität L. von Grafenstein, Übungen, 2 SWS (Humboldt-Univer- Berlin, WS 2017/18): Röntgenphysik I sität zu Berlin, WS 2018/19): Physik III Optik

S. Eisebitt together with M. Krikunova and B. Kanngießer, M. J. J. Vrakking, Vorlesung, 2 SWS (Freie Universität Vorlesung, 2 SWS (Technische Universität Berlin, WS Berlin, WS 2017/18): Ultrafast Laserphysics 2017/18): Optik und Photonik I M. J. J. Vrakking, Übungen, 2 SWS (Freie Universität S. Eisebitt together with B. Kanngießer and T. Möller; Berlin, WS 2017/18): Ultrafast Laserphysics Vorlesung und Übungen, 4 SWS (Technische Universität Berlin, SS 2018): Röntgenphysik II M. J. J. Vrakking, Vorlesung, 2 SWS (Freie Universität Berlin, WS 2018/19): Ultrafast Laserphysics S. Eisebitt, together with B. Kanngießer and T. Möller; Vorlesung und Übungen, 4 SWS (Technische Universität M. J. J. Vrakking, Übungen, 2 SWS (Freie Universität Berlin, WS 2018/19): Röntgenphysik I Berlin, WS 2018/19): Ultrafast Laserphysics

T. Elsaesser together with G. Steinmeyer, Vorlesung T. Witting, Übungen, 2 SWS (Humboldt-Universität zu und Übungen, 4 SWS (Humboldt-Universität zu Berlin, Berlin, WS 2018/19): Physik III Optik SS 2018): Physik ultraschneller Prozesse (Kurzzeitspek- troskopie) M. Woerner, Übungen, 2 SWS (Humboldt-Universität zu Berlin, WS 2018/19): Laserphysik T. Elsaesser together with K. Busch, Vorlesung, 4 SWS (Humboldt-Universität zu Berlin, WS 2018/19): Laserphysik

I. V. Hertel, Seminar, 2 SWS (Humboldt-Universität zu Berlin, WS 2017/18): Forschungspraktikum mit Seminar General talks (popular, science politics etc.) I. V. Hertel, Seminar, 2 SWS (Humboldt-Universität zu Berlin, WS 2018/19): Forschungspraktikum mit Seminar S. Eisebitt, Verleihung der Röntgen-Plakette der Stadt F. Intravaia, Vorlesung, 2 SWS (Humboldt-Universität zu Remscheid (Remscheid, Germany, 2018-04): Das Un- Berlin, SS 2018): Fluktuations-induzierte Phänomene sichtbare sichtbar machen, Laudatio auf den Preisträger Prof. Dr. Franz Pfeiffer F. Intravaia, Übungen, 2 SWS (Humboldt-Universität zu Berlin, SS 2018): Fluktuations-induzierte Phänomene L. von Grafenstein; Carl-Ramsauer-Preisverleihung (Berlin, Germany, 2018-11): Erzeugung ultrakurzer La- F. Intravaia, Übungen, 2 SWS (Humboldt-Universität serpulse mit hoher Energie im mittleren Infrarot zu Berlin, SS 2018): Theoretische Physik III: Quanten- mechanik M. Ivanov, Vorlesung (Humboldt-Universität zu Berlin, WS 2017/18): Quantum dynamics in strong laser fields

M. Ivanov, Übungen (Humboldt-Universität zu Berlin, WS 2017/18): Quantum dynamics in strong laser fields

118 Appendix 3 Ongoing Bachelor, Master, and PhD theses

Bachelor theses F. Branchi; Ultrafast structural dynamics in molecules by time-resolved photoelectron holography (Supervisor: M. D. Dahm; Herstellung und Charakterisierung von Dünn- J. J. Vrakking), Freie Universität Berlin schichtproben mittels Rotationsbeschichtung für zeit- aufgelöste Röntgenabsorptionsspektroskopie (Supervi- F. Brauße; Shape resonances as a probe of an evolving sor: B. Kanngießer and H. Stiel), Technische Universität nuclear and electronic structure in molecules (Supervi- Berlin sor: M. J. J. Vrakking and A. Rouzée), Freie Universität Berlin

Master theses M.-A. Codescu; Ultraschnelle Dynamik von photoin- duzierten Prozessen (Supervisor: T. Elsaesser), Hum- P. Engl; Time-resolved photoelectron spectroscopy boldt-Universität zu Berlin of solvated molecules (Supervisor: M. J. J. Vrakking), Freie Universität Berlin L. Drescher; Attosecond transient absorption spectroscopy (Supervisor: J. Mikosch and M. J. J. Vrakking), L. Glöggler; First pump-probe NEXAFS experiments us- Freie Universität Berlin ing a laser-based plasma source (Supervisor: B. Kan- ngießer and H. Stiel), Technische Universität Berlin E. Escoto; Regularization strategies for advanced laser pulse shape reconstruction (Supervisor: G. Steinmey- K. Kolatzki; Setup and characterization of a helium liquid er), Humboldt-Universität zu Berlin jet for diffraction experiments (Supervisor: D. Rupp and T. Möller), Technische Universität Berlin K. Gerlinger; X-ray imaging of optically induced spin textures (Supervisor: S. Eisebitt), Technische Universi- P. M. Stammer; Attosecond electron dynamics(Supervi- tät Berlin sor: O. Smirnova and F. Morales), Technische Universi- tät Berlin M. Hennecke; Ultraschnelle Spindynamik untersucht mit Femtosekunden-Röntgenpulsen (Supervisor: S. Eise- F. Steinbach; All-optical switching with structured illumi- bitt), Technische Universität Berlin nation (Supervisor: S. Eisebitt), Technische Universität Berlin A.-A. Hernandez Salvador; Femtosekunden-Röntgen- beugung an ionischen Materialien (Supervisor: T. El- F. Trigub; The role of dissipative processes in nonequi- saesser), Humboldt-Universität zu Berlin librium atom-surface interactions (Supervisor: K. Busch and F. Intravaia), Humboldt-Universität zu Berlin P. Hessing; Interferenzbasierte zeitaufgelöste Abbildung und Spektroskopie mit XUV-Strahlung (Supervisor: S. K. Tschernig; Pseudo-energy representation of multi- Eisebitt), Technische Universität Berlin photon processes in multiport systems (Supervisor: K. Busch and A. Perez-Leija), Humboldt-Universität zu E. Ikonnikov; Control of excited state dynamics of sol- Berlin vated molecules by ultrashort shaped laser pulses (Su- pervisor: M. J. J. Vrakking and K. Heyne), Freie Univer- M. Valent; 10 kHz single-cycle pulse compression and sität Berlin attosecond XUV laser source (Supervisor: M. J. J. Vrak- king and C. Frischkorn), Freie Universität Berlin A. Jonas; Zeitaufgelöste Röntgenabsorptionsspek- troskopie mittels einer Laserplasmaquelle an Pig- P. Weber; Generation of ultrashort soft X-ray pulses ment-Proteinkomplexen des Photosyntheseapparates by two-color high harmonic generation (Supervisor: A. (Supervisor: B. Kanngießer and H. Stiel), Technische Rouzée and M. J. J.Vrakking), Freie Universität Berlin Universität Berlin

P. Juergens; Plasma formation during ultrashort pulse laser micromachining of solid dielectrics (Supervisor: M. J. J. Vrakking and T. Baumert), Freie Universität Berlin PhD theses N. Khodakovskiy; Methods of ultrafast laser contrast U. Bengs; Generation of isolated attosecond pulses with diagnostics and optimization (Supervisor: M. J. J. Vrak- circular polarization (Supervisor: M. Ivanov and N. Zha- king and M. Kalashnikov), Freie Universität Berlin varonkov), Humboldt-Universität zu Berlin

119 J. Klei; Attosecond time-resolved molecular electron dy- M. Sauppe; Zeitaufgelöste Experimente an Clustern namics (Supervisor: M. J. J. Vrakking), Freie Universität mit intensiven XUV-Doppelpulsen (Supervisor: D. Rupp Berlin and T. Möller), Technische Universität Berlin

C. Kleine; Ultraschnelle Spektroskopie von Ladung- J. Schauss; Ultrakurzzeitdynamik der Wechselwirkung stransferprozessen untersucht mit weichen Röntgenim- zwischen Ionen und Biomolekülen (Supervisor: T. El- pulsen (Supervisor: T. Elsaesser), Humboldt-Universität saesser), Humboldt-Universität zu Berlin zu Berlin F. Schell; Coincident detection of correlated electron B. Langbehn; X-ray imaging of ultrafast dynamics in and nuclear dynamics induced by ultra short laser puls- single helium nanodroplets (Supervisor: D. Rupp and T. es (Supervisor: C. P. Schulz and M. J. J. Vrakking), Möller), Technische Universität Berlin Freie Universität Berlin

J. Lebendig-Kuhla; Role of delocalized states for the ex- B. Senfftleben; Time resolved diffractive imaging with cited state dynamics of nucleotide oligomers (Supervi- intense attosecond pulses (Supervisor: S. Eisebitt and sor: M. J. J. Vrakking, and A. Lübcke), Freie Universität D. Rupp), Technische Universität Berlin Berlin N. Singh; Development of advanced exchange cor- Q. Li; Ultra long range effects in ultra fast spin dynamics relation kernels with time-dependent density functional (Supervisor: P. Brouwer and S. Sharma) Freie Univer- theory (Supervisor: P. Brouwer and S. Sharma) Freie sität Berlin Universität Berlin

F. Mahler; Spektroskopische Untersuchungen an P. Varytis; Light-path engineering in disordered wave- III-V-Halbleiterstrukturen (Supervisor: T. Elsaesser), guiding systems (Supervisor: K. Busch), Humboldt-Uni- Humboldt-Universität zu Berlin versität zu Berlin

N. Mayer; Generation, characterization, and application D. Weder; Time-resolved investigation of ultrafast mag- of chiral attosecond pulses (Supervisor: M. Ivanov and netization dynamics (Supervisor: S. Eisebitt), Tech- O. Kornilov), Humboldt-Universität zu Berlin nische Universität Berlin

S. Meise; Korrelationen und molekulare Fragmentations- J. Weisshaupt; Ultrakurzzeit-Röntgenmethoden zur Un- dynamiken in starken IR- und FEL-Laserfeldern (Super- tersuchung struktureller Dynamik in Festkörpern (Su- visor: U. Eichmann), Technische Universität Berlin pervisor: T. Elsaesser), Humboldt-Universität zu Berlin

N. Monserud; Photo-induced dynamics in molecule F. Willems; The role of transport processes in ultrafast photo-induced dynamics on the sub-femtosecond to demagnetization dynamics (Supervisor: S. Eisebitt), few-femtosecond timescale (Supervisor: A. Rouzée and Technische Universität Berlin M. J. J. Vrakking), Freie Universität Berlin H. Zimmermann; Untersuchung angeregter neutraler M. Oelschläger; Theory of fluctuation-induced phenom- Fragmente nach frustrierter Tunnelionisation (Supervi- ena in nanophotonic systems (Supervisor: K. Busch and sor: U. Eichmann), Technische Universität Berlin F. Intravaia), Humboldt-Universität zu Berlin J. Zimmermann; Probing ultrafast electron dynamics in A. F. Ordonez; Ultrafast electronic dynamics in chiral helium nanodroplets with deep learning assisted diffrac- molecules (Supervisor: S. Smirnova), Technische Uni- tion imaging (Supervisor: T. Möller and D. Rupp), Tech- versität Berlin nische Universität Berlin

M. Osolodkov; Attosecond IR pump probe measurements of small molecules using 3D momentum spectroscopy (Supervisor: M. J. J. Vrakking and T. Witting), Freie Universität Berlin

M. Oßwald; Theoretical description and simulation of non-linear spectroscopic signals of the light induced primary processes in (6-4) photolyase (Supervisor: K. Bus- ch and B. P. Fingerhut), Humboldt-Universität zu Berlin

N. Raabe; CEP stabilization of kHz CPA lasers and their application (Supervisor: M. J. J. Vrakking and G. Stein- meyer), Freie Universität Berlin

D. Reiche; Role of material, geometrical and statistics properties in equilibrium and nonequilibrium fluctuation-induced interactions (Supervisor: K. Busch and F. Intravaia), Humboldt-Universität zu Berlin

120 Appendix 4 Guest Lectures at the MBI

K. Guesmi, Laboratoire Charles Fabry - UMR CNRS H. Merdji, LIDYL/Attophysics Laboratory, CEA Saclay, 8501, Groupe Lasers, France; Seminar B, 2018-01-22: France; Seminar A, 2018-04-18: High harmonic genera- Ultrafast laser dynamics and applications tion in 2D and 3D semiconductors

D. Brida, Universität Konstanz; Institutskolloquium, P. Gaal, Hamburg University; Seminar B, 2018-05-03: 2018-01-17: Sub-optical-cycle control of light and matter Magnetoacoustics in thin films and membranes

H. J. Wörner, ETH Zurich, Switzerland; Institutskolloqui- D. Turchinovich, Universität Duisburg-Essen; Seminar um, 2018-01-31: Attosecond science in the liquid phase C, 2018-05-03: Direct look at charge, lattice and spin dynamics in solids with ultrafast terahertz spectroscopy C. Hauri, Paul Scherrer Institut, Villingen, Switzerland; Institutskolloquium, 2018-02-14: Terahertz field-driven L. Bruder, Universität Freiburg; Seminar A, 2018-05-22: nonlinearities in optical media and light-sound conver- A promising approach for coherent multidimensional sion in 3D graphene sponge spectroscopy with XUV photons

A. Cavalleri, Max Planck Institute for the Structure and P. Wernet, Helmholtz-Zentrum Berlin für Materialien und Dynamics of Matter, Hamburg/Department of Physics, Energie GmbH – BESSY II, Berlin; Seminar C, 2018-05- University of Oxford, UK; Institutskolloquium, 2018-02- 31: Mapping chemical interactions and dynamics with 21: Advances in nonlinear phononics femtosecond X-ray pulses

L. Cattaneo, Ultrafast Laser Physics Laboratory, ETH M. Helm, Helmholtz-Zentrum Dresden-Rossendorf e.V.; Zurich, Switzerland; Seminar A, 2018-02-09: Nucle- Institutskolloquium, 2018-06-13: THz spectroscopy of ar-electronic coupled photoionization dynamics of H2 solids with a free-electron laser

C. Papadopoulou, University of Ioannina, Greece; Sem- A. Kheifets, Research School of Physics, Australian Na- inar B, 2018-02-23: Ultrafast dynamics of toluene and tional University, Canberra, Australia; Seminar A, 2018- derivatives in the vacuum-ultraviolet region 07-09: Interpreting RABBITT and AttoClock determination of timing of photoemission processes in atoms and A. S. Wyatt, Central Laser Facility STFC Rutherford molecules Appleton Laboratory, UK; Seminar A, 2018-03-02: De- velopments and upgrades on the Artemis Laser Facility C. Vozzi, Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche (CNR-IFN), Italy; Institutskol- C. Netzel, Ferdinand-Braun-Institut, Materialtechnolo- loquium, 2018-07-04: Novel approaches for high-order gie; Seminar C, 2018-03-01: Lokalisation in (Al,In)GaN harmonic spectroscopy of atoms and molecules - Auswirkungen auf die Lumineszenzeigenschaften M. Beye, DESY (FS-FLASH) Hamburg; Seminar B, C. Saraceno, Ruhr University Bochum; Seminar A, 2018-07-12: Towards nonlinear X-ray spectroscopy with 2018-03-12: Modelocked thin-disk lasers as compact FELs drivers for high-power XUV to THz sources B. Seifert, Pontificia Universidad Católica de Chile, San- T. Feigl, optiX fab GmbH; Seminar B, 2018-03-09: Re- tiago de Chile, Chile; Seminar C, 2018-07-04: Analytic search activities of optiX fab GmbH, Multilayer mirrors reconstruction of two different pulses from double spec- for the water window, and Soft x-ray optics with IR-su- trograms alone pression E. Pines, Ben Gurion University of the Negev, Beershe- A. G. Dijkstra, University of Leeds, UK; Seminar C, va, Israel; Seminar C, 2018-06-21: The CN stretch re- 2018-03-22: Shining light on large molecular complexes porting on the structure of the second and third solvation shell of the Zundel cation in acetonitrile A. Demircan, Institute of quantum Optics, Leibniz-Uni- versität; Seminar C, 2018-04-26: All-optical control with M. Aeschlimann, Technische Universität Kaiserslautern; group-velocity matching Institutskolloquium, 2018-07-11: Probing ultrafast electron and spin dynamics in momentum, space, and time M. Münzenberg, Institute of Physics, Greifswald Univer- sity; Institutskolloquium, 2018-05-16: Ultrafast magne- P. Kuswik, Institute of Molecular Physics Polish Acad- tism and THz spintronics emy of Sciences, Deptartment of Thin Films Poznań, Poland; Seminar B, 2018-09-24: Dzyaloshinskii-Moriya interaction in Co/NiO layer systems

121 P. Bunker, Steacie Laboratory, National Research Council of Canada, Canada; Seminar A, 2018-09-17: The Planck Constant: Its units, history and relation to the 2019 definition of the kilogram

Y. Mairesse, CELIA and University of Bordeaux, France; Seminar A, 2018-10-22: Ultrafast measurements of ultrafast dynamics of chiral molecules

A. Bandrauk, University of Sherbrooke, Quebec, Can- ada; Seminar A, 2018-10-26: Strong field dynamics in tailored laser fields

V. Yakovlev, MPQ Garching; Seminar A, 2018-10-25: Towards petahertz photonics

I. Babushkin, Leibniz Universität Hannover; Seminar A, 2018-11-01: Signatures of attosecond-scale ionization dynamics in low-order Brunel harmonics

W. Widdra, Martin-Luther-Universität, Halle-Wittenberg; Institutskolloquium, 2018-11-14: Photoemission and double photoemission with femtosecond high-harmonic generation sources

J. Czarske, TU Dresden, Seminar C, 2018-11-15: Wave- front shaping in biophotonics

122 Total Others (EFRE, contracts with research insti - tutes etc.) SAW DFG (incl. loan collection) Source of income Products & Service (Industry) EU Country Federal Total amounts spent in 2018: 3.762.773 Euro 0 500.000

4.500.000 3.500.000 3.000.000 2.500.000 2.000.000 1.500.000 1.000.000 Amount (Euro) Amount Appendix 5 Grants and Contracts

123 Appendix 6 Activities in Scientific Organizations

A. A. Andreev Member, Int. Advisory Committee, Int. Workshop on Na- noscale Spectroscopy and Nanotechnology Vice-chair, Editorial Board, Optical Journal Member, RACIRI Summer School Scientific Committee Vice-chair of the Program Committee, 18th Int. Con- ference on Laser Optics, ICLO 2018, (St. Petersburg, Russia) T. Elsaesser

Secretary of the Mathematics and Science Class, Berlin D. Ayuso Brandenburg Academy of Sciences

Member, Committee QUTIF-Young Researcher Meeting Member of the Board, Berlin Brandenburg Academy of (Quantum Dynamics in Tailored Intense Fields), (Berlin, Sciences Germany) Member, IRIS Adlershof, Humboldt-Universität zu Berlin

W. Becker Chair, Physics Group, Gesellschaft Deutscher Natur- forscher und Ärzte (GdNÄ) Member, Editorial Board, Appl. Sci. Associate Editor, Struct. Dyn., AIP Member, Editorial Board, Laser Phys. Lett. Member, Editorial Board, Chem. Phys. Lett. Member, Editorial Board, Science open Member, Science Policy Committee, SLAC, Menlo Park Member of the Advisory and Program Committee, 27th Int. Laser Physics Workshop - LPHYS’ 18 (Nottingham, Member, Proposal Review Panel for the LCLS X-ray UK) FEL facility

Co-chair Seminar 2, Strong Field & Attosecond Physics Member, Peer Review Panel FXE, European XFEL of the 27th Int. Laser Physics Workshop - LPHYS’ 18 (Nottingham, UK) Chair, Prize Committee Ellis R. Lippincott Award, OSA

Member, Advisory Board, Conference Series on Time K. Busch Resolved Vibrational Spectroscopy

MC Substitute member EU-COSTMP1403 Nanoscale Member, Advisory Board, Int. Conference on Coherent Quantum Optics Multidimensional Spectroscopy

Deputy Editor, J. Opt. Soc. B of America B F. J. Furch

S. Eisebitt Ambassador 2018, OSA, The Optical Society (Washing- ton DC, USA), from 2018-06 Member, BMBF Gutachterausschuss

Member, DESY Photon Science Committee U. Griebner

Chair, Scientific Advisory Committee (SAC) of the Eu- Member, Program Committee, EPS-QEOD Europhoton ropean XFEL Conference 2018 (Barcelona, Spain)

Member, Komitee für Forschung mit Synchrotronstrah- Member, Program Committee, Int. Conference on Laser lung (KFS) Optics 2018 (St. Petersburg, Russia)

Member, Extended Governing Board of the Ioffe-Rönt- gen-Institute (IRI)

124 R. Grunwald I. Radu

Member, Editorial Advisory Board, The Open Optics Member, National Advisory Committee, JEMS 2018 Journal, Bentham Open (Joint European Magnetic Symposia) Int. Conference (Mainz, Germany) Member, Editorial Board, Sci. Rep. Member, Peer Review Panel, Diamond Synchrotron Program Committee, Complex Light and Optical Forces, Light Source (Didcot, UK) Photonics West, SPIE

Member, Editorial Board, Appl. Sci. (MDPI) A. Rouzée

Editor, Advanced in Physics X M. Ivanov

Instructor, 2nd training school of new computational O. Smirnova methods for attosecond molecular processes (Zarago- za, Spain) Member, Scientific Advisory Board of the Conference Time and fundamentals of quantum mechanics in 2019, Weizmann Institute of Science, Rehovot, Israel M. P. Kalashnikov Member, Committee SILAP 2018, Super-Intense La- Member of the Advisory and Program Committee, 27th ser-Atom Physics Int. Workshop (Toronto, Canada) Int. Laser Physics Workshop - LPHYS’ 18 (Nottingham, UK) Member, Committee ATTO 2019, 7th Int. Conference on Attosecond Science and Technology (Szeged, Hungary) Co-chair Seminar 4, Physics of Lasers of the 27th An- nual Int. Laser Physics Workshop (LPHYS’18) (Notting- Member, General Committee ICPEAC 2019, Int. Con- ham, UK) ference on Photonic, Electronic and Atomic Collisions (Deauville, France)

T. Nagy G. Steinmeyer Senior member, OSA, The Optical Society of America (Washington DC, USA) General Chair, Program Committee, High-Intensity La- sers and High-Field Phenomena, HILAS 2018 Chair, HILAS 2018 Conference (Strasbourg, France) Voting member, Quantum Electronics and Optics Divi- sion (QEOD) of the European Physical Society (EPS) E. Nibbering Co-Chair, CLEO/Europe Focus Meeting, 44th European Member, Scientific Selection Panel, Helmholtz-Zentrum Conference on Optical Communication (Rome, Italy) Berlin - BESSY II Member, Editorial Board, Phys. Rev. A Member, Editorial Board, J. Photochem. Photobiol. A Session Convener, Special Session on advances in Member, Program Committee, TRVS Time Resolved Vi- ultrafast pulse characterization techniques, 2nd URSI brational Spectroscopy Atlantic Radio Science Conference (AT-RASC 2018) (Maspalomas, Spain) Member, Proposal Review Panel, Linac Coherent Light Source LCLS Committee Member, Symposium on Ultrafast and Non- linear Optics, CLEO Pacific Rim, Hongkong 2018

V. Petrov Associate Editor, Optica

Associate Editor, Opt. Lett. Guest Editor, J. Sel. Top. Quant. Electron.

Member, Int. Program Committee Advanced Laser Member, Editorial Board, Phys. Lett. A Technologies (ALT) and Co-Chair of Laser Section (Tar- ragona, Spain) Committee Member, 3rd EPS Prize for Research into the Science of Light

Member, Program Committee (Bol, Croatia), Ultrafast Optics 2019

Topical Editor, Opt. Lett.

125 H. Stiel Honors and awards

Member of the Advisory and Program Committee, In- L. von Grafenstein: Carl-Ramsauer-Preis, Humboldt-Uni- ternational Conference on X-ray lasers (Prague, Czech versität zu Berlin (Berlin, Germany) Republic) P. Jürgens: Alexander Glass Best Oral Presentation Award, together with T. Witting, A. Husakou, M. Ivanov, J. W. Tomm M. J. J. Vrakking, and A. Mermillod-Blondin, SPIE Laser Damage (Boulder, USA) Permanent Member, Int. Steering Committee, Int. Con- ference on Defects - Recognition, Imaging and Physics D. B. Milošević: Georg Forster-Forschungspreis der Al- of Semiconductors, DRIP (Berlin, Germany) exander von Humboldt-Stiftung (Berlin, Germany)

Member, Scientific Committee of the Semiconductor D. Rupp: Karl-Scheel-Preis, Physikalische Gesellschaft nanostructures towards electronic & opto-electronic de- zu Berlin PGzB (Berlin, Germany) vice applications VII, Conference of the E-MRS 2019 D. Rupp: Berliner Wissenschaftspreis des Regieren- Member, Editorial Board, J. Electron. Mater. den Bürgermeisters Michael Müller in der Kategorie Nachwuchspreis (Berlin, Germany) Member, Editorial Board, J. Commun. Phys.

Member, Program Committee, 29th European Sympo- sium on Reliability of Electron Devices, Failure Physics and Analysis (Aalborg, Denmark)

M. J. J. Vrakking

Permanent Member, CEA’s Visiting Committee advising the CEA high commissioner chairman of artemis access board

Chairman, SAC of the Advanced Research Centre for Nanolithography (Amsterdam, Netherlands)

Chairman, SAC of the EUCALL Integrated Infrastruc- tures Network

Chairman, Access Panel of the ARTEMIS user facility at RAL (Oxford, UK)

Member, Laserlab Europe III & IV, Management Board

Member, ERC Panel for Fundamental Constituents of Matter in the Advanced Grant 2018 evaluation (Brus- sels, Belgium)

Chair, DPG Fachverband Atomphysik (A), Sektion Atome, Moleküle, Quantenoptik und Plasmen

Editor-in-chief, J. Phys. B

Chairman, Physics faculty evaluation panel (Freiburg, Germany), University of Freiburg

President, SAB of CILEX-APOLLON (Palaiseau cedex, France), Ecole Polytechnique

Member, Proposal review panel of LCLS FEL

Member, Project review panel of FLASH FEL

Chairman, Applied physics faculty evaluation panel (Eindhoven, Netherlands), Eindhoven University of Technology

126 t Max-Born-Straße 2 A 12489 Berlin Prof. Dr. M. J. Vrakking Prof. Dr. S. Eisebit Prof. Dr. T. Elsaesser from there: Bus 162, 164 to Magnusstraße Tram: 61, 63 to Karl-Ziegler-Straße from there: Bus 162 to Magnusstraße Max-Born-Institut (MBI) für Nichtlineare Optik und Kurzzeitspektroskopie im Forschungsverbund Berlin e. V. Mail Address: Max-Born-Institut Germany Phone: Fax: [email protected] (++49 30) 6392 1505 www.mbi-berlin.de (++49 30) 6392 1519 The Divisions of the Max-Born-Institut Division A: Attosecond Physics Division B: Transient Electronic Structure and Nanoscience Division C: Nonlinear Processes in Condensed Matter City district: Berlin Treptow-Koepenick Subdistrict: Berlin-Adlershof Site: Street: S-Bahn: Berlin-Adlershof Max-Born-Straße 2 A Station: S45, S46, S85, S8, and S9 Berlin-Adlershof Subway: Station: U7 Rudow

127 163

Stand: 31.01.2017 Stand:

260 260 163

Am Studio

Flughafen Berlin-Schönefeld / BER ->

163

164

63 164

61 164 Dörpfeldstraße

Adlershof

Ernst-Augustin-Straße Ernst-Augustin-Straße Ernst-Augustin-Straße Ernst-Augustin-Straße Ernst-Augustin-Straße Ernst-Augustin-Straße Ernst-Augustin-Straße Ernst-Augustin-Straße Ernst-Augustin-Straße

Richard-Willstätter-Straße Richard-Willstätter-Straße Richard-Willstätter-Straße

Volmerstraße 63 platz Franz-Ehrlich-Straße W.-Schwabe-

Straße

Havestadt- 61

Straße Straße Straße Straße Straße Straße 260

260

M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler- M.-Seeler-

Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße Justus-von-Liebig-Straße

164 163

Am Studio

162

Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße Max-Planck-Straße

Straße W.-Nernst-

Wagner-Régeny-Straße

Merlitzstraße Merlitzstraße Merlitzstraße

Merlitzstraße G.-Kirchhoff-Straße

Straße

G.-Leibniz- Magnusstraße

Hans-Schmidt-Straße Hans-Schmidt-Straße Hans-Schmidt-Straße Hans-Schmidt-Straße Hans-Schmidt-Straße Hans-Schmidt-Straße Hans-Schmidt-Straße Hans-Schmidt-Straße

163 Chaussee

zeile zeile zeile zeile zeile zeile zeile zeile zeile zeile

Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler- Rumpler-

Rudower Albert-Einstein-Straße

Erich-Thilo-Straße Albert-Einstein-Straße

Pfarrer-Goosmann-Straße Pfarrer-Goosmann-Straße Pfarrer-Goosmann-Straße

Newtonstraße

Kekuléstraße Kekuléstraße

Zum Großen Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Windkanal Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Großen Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Zum Großen Windkanal Großen Zum straße

straße straße straße straße straße straße straße straße straße straße straße straße straße Rutherford-

Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker- Kronecker-

Georg-Schendel-Straße Georg-Schendel-Straße

Brook-Taylor-Straße

Boveristraße Boveristraße Boveristraße

164

Max-Born-Straße 162

Zum Trudelturm Trudelturm Trudelturm Trudelturm Zum Zum Zum Zum

Groß-Berliner Damm Trudelturm Zum

Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße Abram-Joffe-Straße

Newtonstraße Wegedornstraße 160 162 164

Katharina-Boll-Dornberger-Straße 163 63

61 Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße Wilhelm-Hoff-Straße

Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße Konrad-Zuse-Straße

Max-Born-Institut

160

Carl-Scheele-Straße Carl-Scheele-Straße Carl-Scheele-Straße

Ludwig-Boltzmann-Straße Ludwig-Boltzmann-Straße Ludwig-Boltzmann-Straße Ludwig-Boltzmann-Straße Ludwig-Boltzmann-Straße Ludwig-Boltzmann-Straße

Bendemannstraße Bendemannstraße Bendemannstraße

straße Schwarzschild- Alexander-von-Humboldt-Weg Ernst-Ruska-Ufer

Karl-Ziegler-Straße

Straße

Rudower Chaussee Rudower

Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler- Friedrich-Wöhler-

Johann-Hittorf-Straße Johann-Hittorf-Straße Johann-Hittorf-Straße Johann-Hittorf-Straße Johann-Hittorf-Straße North-Willys-Straße

<- Innenstadt James-Franck-Straße

Betriebsbahnhof Schöneweide Betriebsbahnhof

Barbara-McClintock-Straße Ernst-Lau-Straße Hermann-Dorner-Allee

Groß-Berliner Damm 128 Schöneweide

160

Eisenhutweg

Flughafen Berlin-Schönefeld / BER -> usfahrt Adlershof usfahrt A

<- Innenstadt

Eisenhutweg

160 Stubenrauchstraße usfahrt Stubenrauchstraße A