IAMPI2006 International Conference on the Interaction of Atoms, Molecules and Plasmas with Intense Ultrashort Laser Pulses 1 - 5 October, 2006 - Szeged, Hungary

HU1100086

Organized by:

COST - European Cooperation in the Field of Scientific and Technical Research XTRA - Marie-Curie Research Training Network of the European Community Hungarian Academy of Sciences University of Szeged Book of Abstracts with the program of the conference Main sponsor of the conference: FEMTO LASERS FEMTOLASERS Produktions GmbH

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Sponsors:

Hungarian Academy of Sciences • http://www.mta.hu/index.php?id=english

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©Spectra-Physics NewporExperience I Solutiont s A Dftrtsíön ol Newport Corporation Spectra-Physics a Division of Newport Corporation nttp://www.spectraphysics.com

Organizers of the conference highly appreciate the generous support of the exhibitors and sponsors IAMPI2006

International Conference on the Interaction of Atoms, Molecules and Plasmas with Intense Ultrashort Laser Pulses 1-5 October, 2006 - Szeged, Hungary

Organized by:

On behalf of the Local Organizing Committee it is a great pleasure to welcome you to Szeged, on the occasion of IAMP12006, the International Conference on the Interaction of Atoms, Molecules and Plasmas with Intense Ultrashort Laser Pulses.

We hope that you will enjoy the meeting and that your interaction with your colleagues from many different countries will stimulate a creative exchange of ideas and will be personally rewarding.

Feel yourself at home in Szeged, Hungary.

István Földes Chairman

Scope of the Conference

Ultrashort laser pulses reaching extra high intensities open new windows to obtain information about molecular and atomic processes. These pulses are even able to penetrate into atomic scalelengths not only by generating particles of ultrahigh energy but also inside the spatial and temporal atomic scalelengths. New regimes of laser-matter interaction were opened in the last decade with an increasing number of laboratories and researchers in these fields. The interactions with visible light in this parameter range also result in new radiation sources, such as soft and hard X-rays, gamma rays, moreover energetic particles (electrons, protons, heavy ions, and neutrons) are also generated. Even nuclear reactions such as fusion and fission can be effectively driven by strong laser pulses. Most of these intrinsically nonlinear interactions are occurring in plasmas, therefore it is no surprise that high-intensity physics have been strongly motivated since the beginning by the controlled thermonuclear fusion researches. On the other hand attosecond pulses even allow control and real-time observation of electron dynamics at sub-atomic dimensions.

This Conference which joins the ULTRA COST activity ("Laser-matter interactions with ültra-short pulses, high-frequency pulses and ultra-intense pulses. From attophysics to petawatt physics") and the XTRA ("Ultrashort XUV Pulses for Time-Resolved and Non- Linear Applications") Marie-Curie Research Training Network, intends to offer a possibility to the members of both of these activities to exchange ideas on recent theoretical and experimental results on the interaction of ultrashort laser pulses with matter giving a broad view from theoretical models to practical and technical applications. General information

International Scientific Programme Commitee

C.J. Joachain (Université Libre de Bruxeltes, Bruxelles, Belgium) (Co-Chairman) F. Krausz (Max-Planck-Institute of Quantum Optics, Garching, Germany) (Co-Chairman) M. Vrakking (FOM Institute, AMOLF, Amsterdam, The Netherlands) (Co-Chairman) S. Atzeni (Universita' "La Sapienza" di Roma, Roma, Italy) D. Batani (Universita' Milano-Bicocca, Milano, Italy) D. Charalambidis (University of Crete, IESL-FORTH, Heraklion, Greece) Gy. Farkas (Research Institute for Solid State Physics and Optics, Budapest, Hungary) N. Kroó (Research Institute for Solid State Physics and Optics, Budapest, Hungary) A. Maquet (Universite Pierre et Marie Curie, Paris, France) J. Meyer-ter-Vehn (Max-PIanck-Institute of Quantum Optics, Garching, Germany) P. Monot (CEA- Saclay, France) P. Salieres (Centre d'Etudes de Saclay, France) S. Szatmári (University of Szeged, Hungary) G. Szabó (University of Szeged, Hungary) K. Taylor (Queen's University Belfast, Northern Ireland, UK) J. Ullrich (Max-Planck-Institut fiir Kernphysik, Heidelberg, Germany) C.-G. Wahlström (Lund Institute of Technology, Lund, Sweden) Kaoru Yamanouchi (The University of Tokyo, Japan)

Invited lecturers

Jan Badziak (Poland) Eric Mével (France) Philippe Balcou (France) Peter Mulser (Germany) Dimitri Batani (Italy) Mauro Nisoli (Italy) Eckhart Förster (Germany) Bedrich Rus (Czech Republic) Antonio Giulietti (Italy) Csaba Tóth (USA) Hugo van der Hart (UK) George Tsakiris (Germany) Christof H. Keitel (Germany) Paris Tzallas (Greece) Mathias Kling (The Netherlands) Edmond Turcu (UK) Victor Malka (France) Thorsten Uphues (Germany) Alfred Maquet (France) Sándor Varró (Hungary) Jon Marangos (UK) David Villeneuve (Canada) Johan Mauritsson (Sweden) Kaoru Yamanouchi (Japan) Jose Tito Mendon?a (Portugal) Matthew Zepf (UK) Jiirgen Meyer-ter-Vehn (Germany) Vladimir Zvorykin (Russia) General information

Local Organizing Committee

István Földes (chairman) KFKI-Research Institute for Particle and Nuclear Physics Department of Plasma Physics, Budapest, Hungary e-mail: [email protected] fax: +36-1-395-9151

Péter Dombi Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, Budapest, Hungary e-mail: [email protected] fax: +36-1-392-2215

Katalin Varjú Department of Optics and Quantum Electronics University of Szeged, Szeged, Hungary e-mail: [email protected]

Rita Dajka / Organizing Secretary Department of Experimental Physics, University of Szeged, Szeged, Hungary e-mail: [email protected] fax: +36-62-420-154

Conference Secretariat/Organizing Office (registration, accommodation, abstracts, payment)

CONGRESS & HOBBY SERVICE Postal address: P.O.Box 1022, H-6701 Szeged, Hungary Phone: +36-62-484-531 Fax: +36-62-450-014 e-mail: [email protected] General information

Venue Hotel Forrás*** Address: Szent-Györgyi Albert utca 16-24. H-6726 Szeged, Hungary Phone: + 36-62-566-466; Fax: + 36-62-566-468

Dates 1 October (Sunday) - 5 October (Thursday), 2006

Language The official language of the IAMPI2006 is English.

Registration/Information desk You should collect your conference documentation (congress kit, final program & abstract booklet, badge, entry tickets) at the registration desk upon your arrival. The files of the oral presentations will be collected and uploaded to our computer at the registration desk. The staff at the registration desk will be pleased to assist you with all your inquiries. The registration desk will be open in the lobby of Hotel Forrás (Conference Venue) as follows:

30 September, 2006 (Saturday) 14:00 - 20:00 hours 1-4 October 08:00 - 18:00 hours 5 October, 2006 (Thursday) 08:00 - 16:00 hours

Phone (mobile) +36-30-985-4191 (between 30 September - 5 October, 2006 only)

Registration fees (in Euro) before 15 July, 2006 after 15 July, 2006 regular € 250 € 280 accompanying persons €100 €100

The registration fee of the participants includes: •S admission to the scientific sessions S program & abstract booklet' •S conference bag, name badge S conference dinner (4 October) •S welcome cocktail (1 October) S coffee breaks •f excursion (3 October)

The registration fee of the accompanying persons includes: name badge S conference dinner (4 October) welcome cocktail (1 October) S coffee breaks •S excursion (3 October)

Payment on-site Your final invoice/bill will be completed upon registration. Payments in advance (bank transfer, cheque) will be accepted on your final invoice / bill. Those who did not pay in advance the total sum can pay the difference at the registration by cash. The following currencies will be accepted for payment on site: Euro, US $, and Hungarian Forints (HUF). The exchange rates are as follows (in Sept. 2006): 1 Euro =270 HUF and 1 USD ~ 212 HUF. General information

Badge

Participants are requested to wear their badge at all times during the conference.

Oral presentation All speakers are requested to come to the "Speakers desk" located in the registration area and hand in their presentations to the technicians upon arrival. It is expected that the speakers bring their presentations in PowerPoint (MS Office XP or earlier) in pdf or in postscript format. Please bring your presentation on DVD/CD-ROM, USB memory sticks or floppy disc and check it with the preview technical staff. Use embedded pictures and animations only; picture and animation links to the Internet or to other files will not be accessible. If you have any special requirements, please notify the organizers about it well before the conference. An overhead projector will be at your disposal, too. Poster presentation The poster exhibition will be held in the lobby of Hotel Forrás throughout the entire conference. A board, labelled with the abstract number will be available to those who present posters. Presenters are requested to display the poster on the designated board upon arrival. Size of the poster board is 100 cm wide x 120 cm high (portrait orientation).

Poster session: 2 October, 2006 (Monday) 18:10 - 20:00 hours We request the presenters to be at their posters during this time.

Messages

A message board is located in the lobby opposite the registration desk.

Internet access Internet access with e-mail facility is freely available in room "Vaszy Viktor" on the 2nd floor. Prepayed cards for WiFi can also be bought at the hotel reception. Coach transfer The organisers will provide coach transfer from the Budapest Ferihegy Airport to Szeged on 30 September, 2006 (Saturday) and back to Budapest on 5 and 6 October, 2006 (Thursday/Friday). In case of sufficient number of participants, the Conference Office can provide coach transfer in special cases, too. A meeting point will be available at the Airport in the main lobby of Ferihegy 2B terminal (Arrivals). Transport tickets cost EUR 25 / one way. Transfers from Szeged to Budapest will start upon the request of the participants. Please check your seat at the registration desk during the conference.

Accommodation The hotel confirmation was sent to all participants with their accommodation booking. General information

Coffee

Coffee, tea and soft drinks will be available during the breaks in the lobby of the hotel.

Lunches Lunches are not included in the registration fee. Lunches ordered in advance will be served in the restaurant of Hotel Forrás. There is a possibility to order extra lunches at the registration or a la carte dishes in the Hotel restaurant or in another nearby restaurant.. Welcome cocktail (included in the registration fees) 1 October, 2006 (Sunday) evening Venue: Study and Information Centre (TIK) of the University of Szeged (Address: Szeged, Ady tér 10.) Welcome drinks, warm and cold light buffet dinner will be served in the Aula of the TIK. Bus transfer will be provided from Hotel Forrás and back.

Excursion to Opusztaszer (included in the registration fees) 3 October, 2006 (Tuesday) afternoon English guided tour by coach to National Historical Memorial Park (30 kms from Szeged) visiting an open-air ethnografic museum, Feszty Panorama Painting and including a dinner in a Hungarian „Csárda". Buses leave from Hotel Forrás at 14.30.

Conference dinner (included in the registration fees) 4 October, 2006 (Wednesday) evening All participants are invited to attend the Conference dinner in the Restaurant of Hotel Forrás.

Insurance The fees (registration, accommodation, transfer, excursion) do not include any kind of insurance. The Organizing Committee and the Conference Secretariat can not accept liability for personal accidents, losses or damage. Health, baggage or accident insurance is recommend- ed and must be taken out in your own country.

Cancellation Cancellations for the conference must be notified in writing before 15 August, 2006 for a full refund, less bank charges. After 15 August, 2006 a cancellation fee of EUR 50 will be charged. All refunds will be made after the conference. No refunds are available after 15 September, 2006. Conference program - 1 October, 2006 (Wednesday)

There are coordinated and chaired (traditional) sessions. The coordinators invited most of the speakers of their sessions, and they are to lead it, thus giving space for interesting, living dis- cussions on a field of current interest.

9.00 Opening ceremony

Morning: Fundamental atomic and molecular processes in intense laser fields Coordinator: Charles Joachain 9.20 Sul A. Maquet: Atoms in Strong Fields: Multiphoton IR-XIJV Ionization 9.55 Su2 K. Yamanouchi: Ultrafast hydrogen migration in hydrocarbon molecules in intense laser fields and formation of hydrogen molecular ions

10.30 . Coffee break

10.50 Su3 H. van der Hart: Recent progress in the application of R-matrix Floquet theory 11.25 Su4 C.H. Keitel: QED, nuclear and high-energy processes in extremely strong laser pulses 12.00 Su5 Th. Uphues: Attosecond time resolved ionisation spectroscopy: Sampling of inner-shell processes in rare gases 12.35 Su6 K-.Z. Hatsagortsyan: Relativistic recollisions with tailored laser pulses

12.55 Lunch break

Afternoon: Laser plasmas Chair: Ferenc Krausz 14.30 5V7, i P. Mulser: Collisionless absorption. Physical mechanisms and related strengths 15.05 SitS , T. Mendonfa: Photon acceleration in the sub-cycle optical domain 15.40 ' Su9 ' A. Sagisaka: Characterization of thin-foil preformed plasmas for high-intensity laser plasma interactions

16.00 Coffee break

16.20 SulO A. Giulietti: Search for stable propagation of intense laser pulses in gas 16.55 Suli J. Limpouch: K-a emission from medium and high-Z materials irradiated by < femtosecond laser pulses 17.15 Sul2 E. Förster: Advanced X-ray Spectroscopy for Investigation of Hot Dense . .. . i Plasmas 17.55 ; Sul3 C. Deiss: X-ray generation by laser-cluster interaction 18.15 SuI 4 A Andreev: Interaction of ultra-high intensity laser pulse with a mass limited targets

Evening: Welcome cocktail in the new Study and Information Centre (TIK) of the University of Szeged. Bus transfer provided from Hotel Forrás and back. Conference program - 2 October, 2006 (Wednesday)

Morning: Fast particle generation by ultrashort laser pulses : Coordinator: Jtirgen Meyer-ter-Vehn 9.00 Mol J. Badziak: Production of collimated high-current ion beams by short-pulse lasers 9.35 Mo2 M. Geissler: Bubble regime of wake field acceleration with few cycle laser pulse 10.10 Mo3 A.S. Pirozhkov: Super-high frequency upshifting in the nonlinear interaction of laser pulse with breaking wake wave

10.30 Coffee break

10.50 Mo4 Cs. Tóth: GeV electron beams from table-top laser-plasma accelerator using capillary waveguides 11.25 Mo5 V. Malka: Laser plasma accelerators 12.00 Mo6 D. Batani: Direct evidence of electric fields and fast electron slowing down , during propagation in high-intensity laser matter interaction 12.35 Mo7 O. Klimo: Propagation of high-current fast electron beam in a dielectric target

12.55 Lunch break

Afternoon: New laser sources Chair: Matthew Zepf 14.30 Mo8 J. Meyer-ter-Vehn: Plasma physics with intense VUV radiation 15.05 Mo9 B. Ziaja: Statistical model of radiation damage within an atomic cluster irradiated by VUV photons from FEL 15.25 MolO E.Turcu: Astra-TA1 facility for ultrafast time-resolved science

16.00 Coffee break

16.20 i-Moll • B. Rus: Applications of multi-millijoule soft X-ray lasers in dense plasma physics 16.55 Mol 2 R. Lopez-Martens: High-energy few-cycle pulse compression through 1 self- channeling in gases 17.15 Mol3, V. Zvorykin: Hybrid Ti:Sapphire / KrF laser facility GARPUN for combined < . subpicosecond/ nanosecond laser-matter interaction studies 17.50 Mol4 K. Osvay: A bandwidth independent linear method for detection of carrier : envelope phase drift

18.10-20.00 Poster Session Conference program - 3 October, 2006 (Wednesday)

Morning: Harmonics on solids Chair: Joseph S. Bakos 9.00 Tul S. Varró: Linear and non-linear carrier-envelope phase difference effects in interactions of ultra-short laser pulses with a metal nano-layer 9.35 Tu2 T. Ozaki: Intense harmonic generation from various ablation media 9.55 Tu3 M. Zepf: KeV harmonics in the relativistic limit

10.30 Coffee break

10.50 Tu4 T. Baeva: Relativistic plasma control 11.10 Tu5 G.D. Tsakiris: Intense attosecond pulse source for pump-probe experiments 11.45 Tu6 V.S. Yakovlev: Using shortwave infrared few-cycle pulses for generation of keV harmonics and attosecond pulses 12.05 TtiT" Th. Mercouris: Attosecond time-resolved spectroscopy of electron correlation in excited states 12.25 Tu8 C. Thaury: High-order harmonics generation from overdense plasmas 12.45 Ti<9 T. Desai: Laboratory approach to natural craters, can we?

13.05 Lunch break

Afternoon: Excursion: Opusztaszer, National Historical Memorial Park. Dinner in a Hungarian „Csárda". Conference program - 4 October, 2006 (Wednesday)

Morning: Attosecond physics Chair: Győző Farkas 9.00 We I s E. Mével: Broadband isolated attosecond XUV pulses isolated by CEP- stabilized polarization gating 9.35 ; We2 P. Tzallas: On the characterization of attosecond pulses 10.10 We3 M. De Grazia: Time-resolved luminescence spectroscopy of dielectric crystals under the condition of high excitation density

10.30 Coffee break

10.50 We4 M. Nisoli: Few-cycle isolated attosecond pulses 11.25 • We5 : M. Kling: Carrier-envelope phase control of electron dynamics in atomic and molecular systems 12.00 i We6 A. Kornev: Above-threshold ionization of excited H-states by an ultrashort laser pulse: energy spectra of photoelectrons 12.20 ; We? -. Ph. Antoine: Electron correlation effects in two-photon double ionization of helium 12.40 i We8 C. Ruiz-Mendez: Double ionization in Helium. Ab initio calculations beyond the one dimensional approximation

13.00 Lunch break

Afternoon: High-harmonic generation with molecules Coordinator: Manfred Lein 14.30 i We9 D. Villeneuve: Determining the electronic structure of molecules using high harmonic emission 15.05 We 10 L. Miaja-avila: Molecular and Materials Dynamics Probed by Coherent Electrons from High Harmonic Generation 15.40 .Well- C. Valentin: Optimization of high harmonic generation by genetic algorithm

16.00 Coffee break

16.20 We 12 P. Balcou: Attosecond time-frequency analysis of high-harmonics generation by few cycle laser pulses 16.55 We 13 J. P. Marangos: Imaging molecular structure and dynamics using laser driven recollisions 17.30 We.14 W. Boutu: Measurement of the attosecond emission from aligned molecules 18.05 í We.l 5 Y. Tang: A high average power few-cycle OPCPA drive laser for attosecond pulse production

Evening: ^ Conference dinner Conference program - 5 October, 2006 (Wednesday)

Morning: Time-resolved applications in the subfemtosecond range Chair: Marc Vrakking 9.00 Th 1 J. Mauritsson: Attosecond Pulse Trains Generated using Two Color Laser Fields 9.35 Th2 P. Johnsson: Attosecond Ionization Dynamics 9.55 Th3 : A. Pirri: Direct interferometric measurement of the atomic dipole phase in high-order harmonic generation 10.15 Th4 P. Villoresi: Realization of a time-compensated monochromator exploiting conical diffraction for few-femtosecond XUV pulses

10.35 Coffee break

10.55 Th5 Zs. Major: Short-pulse optical parametric chirped-pulse amplification for the generation of high-power few-cycle pulses 11.15 Th6 X. Xie: Effects of molecular orientation in the laser ionization of molecules 11.35 Th7 C. Vozzi: Generation of high energy self-phase-stabilized near-lR pulses by difference frequency generation and optical parametric amplification 11.55 Th8 J. Fülöp: Shaping of picosecond pulses for pumping optical parametric amplification 12.15 Th9 C. Hauri: Intense carrier-envelope phase stable few-cycle pulses at 2 jim from a filament for high-order harmonic generation 12.35 ThlO J. S. Robinson: Half cycle cut-offs in harmonic spectra and robust carrier- envelope phase retrieval

12.55 Lunch break

14.00-15.00 XTRA Marie Curie Business Meeting

15.00- Visiting the laser laboratories of the University of Szeged Poster session - 2 October, 2006 (Monday)

Pl. A. Aliverdiev, D. Batani, V. Malka, T.Vinci, M. Koenig, A. Benuzzi-Mounaix, R. Dezulian: About an expansion of a high-power-laser produced plasma in vacuum

P2. M. Cerchez, J. Osterholz and O. Willi: Study of close to solid density plasmas generated by ultra-short laser pulses

P3. L. Veisz, K. Schmid, S. Benavides, U. Schramm, S. Becker, J. Fülöp, Zs. Major, J. Osterhoff, S. Karsch, D. Habs, F. Krausz: Laser based quasi-monochromatic electron acceleration

P4. F.F. Körmendi: New nonlinear quantum electrodynamical processes accelerating the . free charged particle in interaction with intense laser radiation

P5. N. Mirnes and A. H. Belbachir: The temperature evolution in a laser heated plasma

P6. B. Gakovic, M. Trtica, P. Panjan, M. Cekada, M. Panjan: Surface modification of multilayered titanium-aluminium nitride coating with high intensity IR laser beam

P7. M. Trtica, B. Gakovic, D. Batani, T. Desai, I. Pongrác: Surface modifications of silicon using the high intensity Nd:YAG laser

P8. M. Lenner, A.Kaplan, Ch. Huchon, R.E. Palmer: Ultrafast laser ablation of graphite

P9. R. Gayet, S. Jequier, V. Rodriguez, H. Bachau G. Duchateau, A. Dyan, H. Mathis : Simulation of primary processes for laser-induced plasma by short laser pubes in KDP crystal

PI 0. l.F. Bama: Two-Photon Ionization of He Atoms through a Superposition of Higher Harmonics

Pl I. M. Boca, V. Florescu and M. Gavrila: A relativistic generelaization of the Kramers- Henneberger transformation

PI2. A. Kornev, B. Zon: Theory of Landau-Dvkhne anddipoleforbidden transitions

PI 3. E. Mese and R. M. Potvliege: The Floquet quasienergy spectrum of rare gases

P14. G. Buica, T. Nakajima: Origin of the side peaks appearing in the above-threshold ionization spectra oj'Mg

P15. V. Stancalie, V. Pais, M. Totolici, A. Mihailescu: Forbidden transitions in excitation by proton impact in Al Li-like ions

PI 6. R. Veilande, I. Bersons: Revival structure of ionization probability for Rydberg atoms

PI7. A.M. Kiselev, A.N. Stepanov, B.A. Tikhomirov, A.B. Tikhomirov: Nonlinear absorption of intense femtosecond laser radiation in molecular gases Poster session - 2 October, 2006 (Monday)

P18. O.F. Kostenko, N.E. Andreev: Heating and ionization ofmetal cluster by intense femtosecond laser field

PI9. Á. Börzsönyi, K. Osvay, A. P. Kovács, M. P. Kalashnikov: Dispersion offemtosecond pulses in vacuum beam lines from ambient pressure down to 0.01 mbar

P20. K. Kosma, S.A. Trushin, W. Fuss, W.E. Schmid: Widely tunable ultraviolet sub-30 fs pulses from supercontinuum for transient spectroscopy

P21. P. Dombi, S. E. Irvine, Gy. Farkas, and A. Y. Elezzabi: Surface-plasmon-ponderomotive electron acceleration as a potential carrier-envelope phase measurement tool

P22. K. Mecseki, M. Erdélyi, A. P. Kovács, and G. Szabó: Cubic Phase Control of Ultrashort Laser Pulses

P23. T. Wittmann, M.G.Schatzel, F. Lindner, G.G.Paulus, A Baltuska, M. Lezius, A. Marcinvevicius, F. Tavela, F. Krausz: Carrier-envelope phase measurement of multiterawatt laser pulses

P24. R. Rakowski, T. Suta, I.B. Földes, S. Szatmári, J. Bohus, A. Bartnik, H. Fiedorowicz, J. Mikolajczyk: Optimization of resonant frequency tripling of KrF laser radiation by gas targets of different lengths

P25. C.P. Hauri, K. Varjú, T.Ruchon, E. Gustafsson, A. L'Huillier, R. López-Martens: Attosecond pulse trains from long laser-gas interaction targets

P26. E. V. Moiseenko, P. Martin, G. Farkas: Generation of very high frequency attosecond pulses with precursors

P27. K. Schiessl, E. Persson, A. Scrinzi, and J. Burgdörfer: Two-Color Driving In High Harmonic Generation: Single-Atom And Pulse Propagation Analysis

P28. E. Persson, K. Schiessl, A. Scrinzi, and J. Burgdörfer: On the generation of attosecond unidirectional half-cycle pulses: inclusion of propagation effects

P29. T. Remetter, T. Ruchon, P. Johnsson, K. Varjú, E. Gustafsson, R. López-Martens, M. Kling, Y. Ni, F. Lépine, J. I. Kahn, M. J. J. Vrakking, J. Mauritsson, K. J. Schafer and A. L'Huillier: Attosecond Electron Wave Packet Interferometry

P30. N. Fedorov, A. Belsky, P. Martin: Application of VUV harmonics light source for investigation of energy transfer mechanisms in the wide band gap solids Abstracts Oral presentations dür>

Atoms in Strong Fields: Multiphoton IR-XUV Ionization Richard Tai'eb and Alfred Maquet Laboratoire de Chimie Physique-Matiére et Rayonnement, (UMR 7614 du CNRS) Université Pierre et Marie Curie, 11, Rue Pierre et Marie Curie, 75 231 Paris Cedex 05, France.

The advent of new sources, either from harmonic generation or from XFEL and x-ray lasers, delivering ultra-short pulses of coherent XUV (or soft-x-ray) radiation with unprecedented high intensities, opens for the first time the exciting possibility to observe non-linear (multiphoton) processes in these frequency domains. In this progress report, we shall discuss several topics related to the physics of this class of phenomena, including the question of the conditions required for observing multiphoton ionization and Above Threshold Ionization (ATI) of atoms with the currently developed sources, in this context, we shall report on recent experiments performed on "multicolor" ionization processes involving both higher harmonics and the radiation of the pump IR laser. We shall also present some recent results regarding two-color ionization processes involving the absorption of XUV photons from the XFEL source at DESY in the presence of a strong IR laser field.

HU1100087 dÜD

Ultrafast hydrogen migration in hydrocarbon molecules in intense laser fields and formation of hydrogen molecular ions Kaoru Yamanouchi Department of Chemistry, School of Science, The University of Tokyo 7-3-1 Hongo, Bimkyo-ku, Tokyo 113-0033, Japan kaoru@chem. s. u-tokyo. ac.jp

It has been shown in a series of our studies on molecules in intense laser fields that geometrical structure of molecules can largely be deformed through a strong coupling between molecules and ultrashort intense laser fields. In our recent investigations on small hydrocarbon molecules, we learned that hydrogen atoms move very rapidly within hydrocarbon molecules, and hydrogen molecular ions, H3"1" and H2+, are efficiently formed when they are exposed to an intense laser field [1], By referring to our recent studies on small hydrocarbon molecules in intense laser fields using the mass-resolved momentum imaging method and the coincidence momentum imaging method [2], we will show how the hydrogen atom migration proceeds [3] and how the ejection of hydrogen molecular ions is induced [4] within the duration of ultrashort intense laser pulses.

[1] Y. Furukawa, K. Hoshina, K. Yamanouchi, H. Nakano, Chem. Phys. Lett. 414, 117 (2005). [2] H. Hasegawa, A. Hishikawa, K. Yamanouchi, Chem. Phys. Lett. 349, 57 (2001). [3] T. Okino, Y. Furukawa, P. Liu, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, and H. Nakano, Chem. Phys. Lett. 423, 220 (2006). [4] T. Okino, Y. Furukawa, P. Liu, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, and H. Nakano, Chem. Phys. Lett. 419, 223 (2006).

HU1100088 HU1100089

Recent progress in the application of R-matrix Floquet theory H.W. van der Hart Department of Applied Mathematics and Theoretical Physics, Queen's University Belfast, Belfast BT7 INN, United Kingdom

R-matrix Floquet theory was developed 15 years ago [1,2] to describe the behaviour of real atomic systems in intense laser fields. The theory combines standard R-matrix theory to describe the atomic structure in detail and the Fourier-Floquet Ansatz to account for interactions due to the laser field. The theory can be employed for laser pulses with duration longer than 5 cycles, and has been applied with great success to a wide range of atoms [3],

Recent developments in the application of R-matrix Floquet theory have focused on three different strands: noble-gas atoms subjected to laser light with near-optical wavelengths, double ionization, and multiphoton emission of inner-shell electrons. The interest in the first strand follows from the experimental and theoretical interest in the behaviour of He subjected to intense 390 nm laser light [4]. We have recently established that the R-matrix Floquet approach can be used to determine He ionization rates at this wavelength for intensities up to 2.5 X 1014 W/cm2, even though ionization requires absorption of at least 9 photons. The accuracy of the approach is excellent: a comparison with time-dependent calculations shows agreement well within 10% [5]. Following this success, we extended the study to other noble-gas atoms of experimental interest, Ne and Ar. For these atoms, ionization requires absorption of at least 8 and 6 photons, respectively.

The two other strands follow the experimental interest in the development of VUV and X-ray lasers, which will open up new avenues for investigation. Only outer electrons respond to a visible-light laser field, whereas all electrons cloud -respond to an X-ray laser field. One example of such a multi-electron response is direct double ionisation of He, subjected to a laser field with photon energy of 45 eV. This process requires absorption of only two photons, one photon fewer than required for sequential double ionisation. This is due to the electron- electron repulsion reducing the He binding energy. Investigations of He at this photon energy thus give new fundamental insight into the nature of electron-electron repulsion.

The description of the collective response of atomic electrons becomes increasingly more difficult with increasing number of atomic electrons. However, R-matrix theory was designed to cope with these difficulties. For example, inner-shell processes involving the absorption of a single photon have been studied extensively using R-matrix theory (eg. [6]). We demonstrate that this capability carries over to R-matrix Floquet theory by investigating the multiphoton emission of an inner-shell Is electron from Li" was chosen, since only a relatively small number of Li target states are necessary to describe the triply excited states of Li" in the calculations.

[1] P.G. Burke, P. Francken, C.J. Joachain, Europhys. Lett. 13, 617 (1990) [2] P.G Burke, P. Francken and C.J. Joachain, J. Phys. B 24, 761 (1991). [3] C.J. Joachain, M. Dörr, and N J Kylstra, Adv. At. Mol. Opt. Phys. 42, 225 (2000) [4] J.S. Parker et al, Phys. Rev. Lett. 96, 133001 (2006). [5] H.W. van der Hart, B.J.S. Doherty, J.S. Parker and K.T. Taylor, J. Phys. B 38, L207 (2005). [6] N. Berrah et al, Phys. Rev. Lett. 87, 253002 (2001). H.W. van der Hart [email protected] QED, nuclear and high-energy processes in extremely strong laser pulses C. H. Keitel, K. Z. Hatsagortsyan, A. Di Piazza and C. Miiller Theory Division Max Planck Institute for Nuclear Physics, Heidelberg, Germany

Relativistic quantum dynamics of atoms and ions is briefly introduced in ultra-intense laser pulses [1], The feasibility of nuclear excitation dynamics is then shown to be realistic with future XFEL light [2]. Quantum electrodynamical processes are then investigated in extremely strong laser pulses [3], Electron-positron pairs may be created in crossed laser fields and the quantum dynamics of positronium displays numerous exciting phenomena, including coherent gamma-ray emission. Finally, emphasis is placed on high-energy processes such as muon pair production from laser-driven positronium [4],

[1] Y. 1. Salamin et al„ Phys. Rep. 427, 41 (2006) [2] T. J. Bürvenich, J. Evers and C. H. Keitel, Phys. Rev. Lett. 96, 142501 (2006) [3] A. Di Piazza, K. Z. Hatsagortsyan, C. H. Keitel, arXiv.org: hep-ph/0602039 [4] C. Müller, K. Z. Hatsagortsyan, C. H. Keitel, arXiv.org: physics/0602106

Christoph H Keitel Theory Division Max Planck Institute for Nuclear Physics PO Box 10 39 80 69029 Heidelberg phone:+49 6221 516-150 fax: +49 6221 516-152 [email protected]

HU1100090 HU1100091

Attosecond Time Resolved Ionisation Spectroscopy: Sampling of Inner-Shell Processes in rare gases Th. Uphues1, M. Uiberacker2, M. Schultze3, A.-J. Verhoef3, V. Yakovlev2, N. M. Kabachnik1-4, H. Schroder3, M. Drescher1-5, U. Kleineberg1, U. Heinzmann1 and F. Krausz2-3 'Fakultát fiir Physik, Universitát Bielefeld, Universitatsstrasse 25, D-33615 Bielefeld, Germany 2Department für Physik, LMU München, Am Coulombwall 1, D-85748 Garching, Germany 3Max-Planck-/nstitut fiir Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany 4 Institute of Nuclear Physics, Moscow State University, Moscow 119992, Russia 5Institutfiir Experimentalphysik, Universitát Hamburg, Luruper Chaussee 149, D-22761 Hamburg, Germany

Relaxation dynamics of core-excited ions was traced by ion-population transfer in the case of XUV excited xenon. Here we demonstrate, that a laser based sampling system, consisting of a few-cycle femtosecond laser pulse and a synchronised sub-femtosecond soft X-ray pulse allows us to sample these dynamics with attosecond resolution. We demonstrate the tracing of inner atomic rearrangement of xenon excited by a 250 as

XUV pulse carried at hcoxuv =93,5 eV with a bandwidth FWHM (full-width at intensity half- maximum (FWHM): tl ~ 5 fs, carrier wavelength: AL = 750 nm, 3kHz repetition rate) of

~9 eV well above the xenon 4d -> 6p resonance. The ionised atoms are probed by a ha>L ~ 1,6 eV laser pulse and detected by an reflectron type time-of-flight ion spectrometer. For weak laser pulses we trace the inner-shell processes by probing the shift in the binding energy of the outer electrons excited by the XUV. In the case of xenon a ha>xuv =93,5 eV photon produces a 4d~' hole, which will decay through different Auger channels and create higher ionic charges [1,2]. Due to Auger-induced shake-up processes or direct excitation the delay dependent ionisation of the excited electron with the IR laser pulse'laser pulse reveals dynamics in the population of the different ionic states, which are related to the decay times of the single and double Auger channels [3,4],

[1] U. Becker, D. Szostak, H. G. Kerkhoff, M. Kupsch, B. Langer, R. Wehlitz, A. Yagishita, T. Hayaishi; Subshell photoionization of Xe between 40 and 1000 eV, Phys. Rev. A 39, 3902-3911 (1989) [2] D M P Holland, K Codling, G V Marr and J B West, Multiple photoionisation in the rare gases from threshold to 280 eV, J. Phys. B: At. Mol. Phys. 12 2465-2484 [3] P. Lablanquie, S. Sheinerman, F. Penent, R. I. Hall, M. Ahmad, T. Aoto, Y. Hikosaka and K. Ito, Photoemission of threshold electrons in the vicinity of the xenon 4d hole: dynamics of Auger decay, J. Phys. B: At. Mol. Opt. Phys. 35 3265-3295 (2002) [4] F. Penent, J. Palaudoux, P. Lablanquie, L. Andric, R. Feifel and J. H. D. Eland, Multielectron Spectroscopy: The Xenon 4d Hole Double Auger Decay, Phys. Rev. Lett. 95, 083002 (2005)

Thorsten Uphues University Bielefeld, Molecular and Surface Physics UniversitatsstarBe 25, D-33615 Bielefeld, GERMANY e-mail: [email protected] dür>

Relativistic recollisions with tailored laser pulses Michael Klaiber, Karen Z. Hatsagortsyan, and Christoph H. Keitel Max-Planck Institut filer Kernphysik, Saupfercheckweg 1 D-69117 Heidelberg, Germany

A new approache to increase the recollision efficiency in the relativistic regime is considered. We employ specially tailored relativistically strong laser pulses in the form of attosecond pulse trains to interact with an atomic system. Due to a special tailoring of the laser pulse, the suppression of the relativistic drift of the ionized electron and a dramatic enhancement of the rescattering probability is shown to be achievable. As an indicator of the strong field recollision phenomena we consider the high harmonic generation process in the tailored pulse. The high harmonic generation rate in the tailored pulse in the relativistic regime is calculated using gauge-invariant version of the strong-field approximation [1], The rate is shown to be increased by several orders of magnitude compared with the case of conventional laser pulses. The energies of the revisiting electron at the atomic core can approach the MeV domain which may open a way for hard x-ray harmonics.

[1] M. Klaiber, K. Z. Hatsagortsyan, and C. H. Keitel, Phys. Rev. A, v.73, No.5 (2006), to be published.

Corresponding author: K. Z. Hatsagortsyan e-mail: [email protected]

HU1100092 Collisionless absorption Physical Mechanisms and Related Strengths P. Mulser1 and D. Bauer2 ' Theoretical Quantum Electronics (TQE), Tech. Univ. Darmstadt, Hochschulstr. 7, D-64289 Darmstadt, Germany 2 Max-Planck-lnstut für Kernphysik, P.O.Box 103980, D-69029 Heidelberg, Germany

At laser intensities beyond 1017 W/cm2 dense matter, i.e. dense gases, liquids, solids, clusters, acquires the major fraction of its energy from the laser in the so-called collisionless regime where collisional electron-ion interaction becomes inefficient owing to drastic shortening of the mutual interaction time. Excellent absorption in this regime is well documented by experiments and a whole variety of particle-in-cell, Vlasov and molecular dynamics simulations. Significant enhancement of laser-matter coupling occurs in extended cluster media. Good absorption, typically 50%, is measured and calculated in solids for sub-ps pulses during the irradiation before substantial rarefaction of the dense matter has set in by the thermal pressure. However, neither the numerous experiments nor the many numerical simulations do tell what the physical mechanisms are by which the necessary phase shift for absorption is induced between current density j and laser electric field E in Poynting's theorem. Linear resonace cannot be invoked because of the missing matching between the plasma and laser frequencies. At least ten different collisonless absorption mechanisms have been proposed, as for example skin layer absorption, sheath inverse bremsstrahlung, stochastic heating, relativistic ponderomotive heating, longitudinal and transverse, linear and nonlinear Landau damping, excitation of surface plasmons,y x B and vacuum heating. A discussion and ordering of the strengt of the individual processes, however, is still missing. In addition, to the authors' view the most efficient absorption mechanism has not been proposed yet. In the presentation we show that at high laser intensities the most significant contribution to collisionless absorption is to be attributed to nonlinear resonance between the laser field and the collective field of the plasma layers. The efficiency of the mechanism is evaluated as a function of laser intensity and it is compared with the efficiency of the above mentioned mechanisms found in the literature.

HU1100093 dü*D>

Photon acceleration in the sub-cycle opical domain J. T. Mendonca CFP, lnstituto Superior Tecnico, 1049-001 Lisboa, Portugal

Photon acceleration processes have been studied in recent years in a variety of physical situations that include, laser wakefield in dense plasmas, phase modulation in optical fibers, polariton wakefields in crystals, and the nonlinear quantum vacuum. Here we focus on plasma physics configurations that will eventually lead to the generation of sub-cycle optical pulses in the near infrared or in the visible. Two different plasma physics configurations will be discussed in detail. First, the spectral broadening of optical pulses, resulting from the formation with relativistic plasma wakefields. Second, the frequency up-shift of tera-hetz radiation, produced by relativistic ionization fronts. Theory based on the photon acceleration approach, simulations using wave kinetic codes, and preliminary experimental results in these two areas are presented. Conditions for the formation of sub-cycle optical pulses are established.

HU1100094 HU1100095 CsüiD

Characterization of thin-foil preformed plasmas for high-intensity laser plasma interactions Akito Sagisaka1, Hiroyuki Daido', Alexander S. Pirozhkov1-2, Koichi Ogura1, Satoshi Oriino1, Michiaki Mori1, Mamiko Nishiuchi1, Akifumi Yogo1, Masataka Kado1, Shu Nakamura'-i|Yoshihisa Iwashita3, Toshiyuki Shirai3, and Akira Noda3 'Advanced Photon Research Center, Japan Atomic Energy Agency: 8-1 Umemidai, Kizu, Kyoto 619-0215, Japan 2Division of Optics, P. N. Lehedev Physical Institute of the Russian Academy of Sciences: 53 Leninskiy prospekt, 119991 Moscow, Russia 3 Institute for Chemical Research, Kyoto University: Gokasho, Uji, Kyoto 611-0011, Japan

High-intensity laser and thin foil interactions produce collimated particles, hard x ray and high-order harmonics. In these cases, the preformed plasma plays an important role for interaction with the high-density thin-foil plasma. Therefore, it is necessary to characterize the preformed plasmas for generating the high-energy particles and x-ray radiations. In this experiment, we characterize the preformed plasmas produced by a high-intensity Ti:sapphire laser with a metal foil target and optimize the proton signals by changing the size of preformed plasma. We use a Tksapphire laser (JLITE-X) at the pulse duration of 250 fs. A p-polarized laser beam is transported into a target chamber. The incident beam is divided into pump and probe beams by a beam splitter. The pump beam is focused by an off-axis parabolic mirror with an F number of 13. The estimated peak intensity is up to ~2xl017 W/cm2 with an energy of 220 mj. The probe beam is frequency-doubled in a KDP crystal. The second harmonic probe beam passed through the target surface. A preformed plasma of 3 urn thick Ti foil target is observed by an interferometer [1], We simultaneously observe the proton signal with time of flight (TOF) proton measurement. The protons with the maximum energy of ~900 keV is produced by controlling the size of preformed plasma. The characterization of preformed plasmas will significantly contribute to describe the relativistic-intensity laser thin-foil interactions for generation of high-energy particles as well as high-order harmonics [2, 3],

[1] A. Sagisaka et al., Appl. Phys. B 78, 919 (2004). [2] A. S. Pirozhkov et al., Phys. Lett. A 349, 256 (2006). [3] A. S. Pirozhkov et al., Phys. Plasmas 13, 013107 (2006).

Akito Sagisaka, sagisaka.akitojaea.go.jp HU1100096 Csüi

Search for stable propagation of intense laser pulses in gas Antonio Giulietti Intense Laser Irradiation Laboratory, IPCF/CNR - http://ilil.ipcf.cnr.it/ Via Moruzzi, I 1-56124 Pisa, Italy

The achievement of conditions for stable and reproducible propagation of powerful pulses focused in gases and plasmas is a key issue for many applications including ICF [1] and particle acceleration by plasma electron waves [2], Particularly in this latter case, though very promising results have been obtained in the last few years in electron acceleration, there is still a poor shot-to-shot reproducibility of the energy and energy spread of the produced electron bunches, as well as a considerable variation in the direction of emission and angular distribution of them. Most of the propagation instabilities, including filamentation and hosing [3, 4], are expected and proved to increase their detrimental effect by increasing the intensity of the focused laser pulse. It seems then reasonable, for the transition from acceleration experiments to practical and reliable "table top" accelerators, to consider the case of laser pulses of not extreme intensity propagating through long accelerating paths, possibly in a guided mode [5,6]. The ultrashort pulses used in experiment of this kind are generated by the CPA (Chirped Pulse Amplification) technique. The CPA pulse is however accompanied by a nanosecond "pedestal" due to the amplified spontaneous emission (ASE), and a picosecond pedestal due to the unavoidable limit in the compression of the chirped pulse. In this presentation we report and discuss experimental results of the propagation of CPA pulses of moderately relativistic intensity in gas: they evidence the effects of the precursor pedestals of the main pulse. Details of great interest were observed for the first time with high quality femtosecond 90-degree interferometry. The interferometric data are also correlated with imaging and spectroscopy data of the laser pulse transmitted through the gas. The most relevant physical features are confirmed by a numerical code which simulates the laser pulse propagation self-consistently with the ionization of the gas.

[1] E. L. Dewald et al., Plasma Phys. Contr. Fusion 47, B405 (2005) [2] T. Hosokai, et al, Phys.Rev. E 73, 036407 (2006) [3] Z. Najmudin et al., CLF Annual Report 1998/99, RAL-TR-1999-062, 18 (1999) [4] B. J. Duda et al., Phys. Rev. Lett. 83, 1978 (1999) [5] H. Sheng et al., Phys. Rev. E 72, 036411 (2005) [6] A. Gamucci et al., in press in Applied Physics B (June 2006)

Co-authors: M. Galimberti, A. Gamucci, D. Giulietti, L. A. Gizzi, P. Koester, L. Labate, P. Tomassini, M. Vaselli ILIL-IPCF/CNR, University of Pisa and Istituto Nazionale di Fisica Nncleare, Italy T. Ceccotti, P. D'Oliveira, T.Auguste, P. Monot, P. Martin CEA-DSM/DRECAM/SPAM, Gifsur Yvette Cedex, France dün>

K-a emission form medium and high-Z materials irradiated by femtosecond laser pulses J. Limpouch1, O. Klimo1, N. Zhavoronkov2, A.A. Andreev3 'Czech Technical University in Prague, FNSPE, Brehova 7, 115 19 Praha 1, Czechia 2Max-Born-Institute, Max-Born-Str. 2 A, 12489 Berlin, Germany 3Institute for Laser Physics, Birzhevaya line 12, 193232 St Petersburg, Russia

Fast electrons are created at the target surface during the interaction of high intensity ultra short laser pulses with solids. Fast electrons penetrate deep into the target where they generate K-a and Bremsstrahlung radiation. Generated high brightness K-a pulses offer the prospect of creating a cheap and compact X-ray source, posing a promising alternative to synchrotron radiation, e.g. in medical application and in material science.. With an increase in laser intensity, efficient X-ray emission in the multi-keV range with pulse duration shorter than few picoseconds is expected. This short incoherent but monochromatic X-ray emission synchronized with laser pulses may be used for time-resolved measurements. Acceleration of fast electrons, their transport and K-a photon generation and emission from the target surface in both forward and backward directions are studied here numerically. The results are compared to recent experiments studying K-a emission from the front and rear surface of copper foil targets of various thicknesses and for various parameters of the laser plasma interaction. One-dimensional PIC simulations coupled with 3D time-resolved Monte Carlo simulations show that account of ionization processes and of density profile formed by laser ASE emission is essential for reliable explanation of experimental data. While sub-relativistic intensities are optimum for laser energy transformation into K-a emission for medium-Z targets, relativistic laser intensities have to be used for hard X-ray generation in high-Z materials. The cross-section for K-a shell ionization of high-Z elements by electrons increases or remains approximately constant within a factor of two at relativistic electron energies up to electron energies in the 100-MeV range. Moreover, the splitting ratio of K-a photon emission to Auger electron emission is favorable for high-Z materials, and thus efficient K-a emission is possible. In our simulations and analytical estimates, laser energy conversion to hard K-a emission greater that 10-4 has been found for laser intensities above 1019 W/cm2. Possible ways to the conversion efficiency enhancement via laser and target optimization are depicted. This work was partly funded by the Czech Ministry of Education, Youth and Sports project LC528. The support by the Czech Science Foundation under project No. 202/06/0801 is gratefully acknowledged.

Presenting author. Prof. Jiri _ Limpouch, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Brehova 7, 11.5 19 Praha 1, Czech Republic, [email protected]

HU1100097 CfuTT) HU1100098

Advanced X-ray Spectroscopy for Investigation of Hot Dense Plasmas Eckhart Förster Friedrich-SchUler University Jena Institute of Optics and Quantum Electronics 1, Max-Wien-Platz D-07743 Jena, Germany

The analysis of the K-shell emission spectra is one of the most efficient tools for the investigation of the creation and evolution of plasmas produced by intense ultrashort laser pulses. Relatively simple x-ray spectrographs consist of energy-dispersive CCD's [1] and wavelength-dispersive flat crystal elements. But, they are at a disadvantage in spectral resolution and luminosity, respectively. Only, space integrated plasma parameters, such as electron temperature and electron density, are usually obtained in connection with relatively simple atomic models. In recent years, several sophisticated instruments and methods have been developed to perform a more precise K-shell plasma diagnostics. By use of concavely bent crystals of ade- quate shape a good compromise of spectral resolution and luminosity of the spectrograph is obtained: Cylindrical crystals are used either in the von Hamos or in the vertical-dispersion Johann scheme [2]. Conical crystals have some advantages in combination with streak cam- eras. Toroidal crystals [3] refocus the emitted x-rays even in two dimensions and may thus lead to a reduction of exposure time. Ellipsoidal highly-oriented pyrolithic graphite crystals [4] provide a very high luminosity and may be used if small spectral ranges are of interest. In comparison of these instruments, features of selected x-ray spectra and1 information about plasma processes, are discussed.

[1] F. Zamponi et al., Rev. Sci. Instrum., 76, 116101 (2005) [2] O. Renner et al., Laser Part. Beams, 22, 25 (2004) [3] T. Missalla et al., Rev. Sci. Instrum., 68, 1288 (1999) [4] I. Uschmann et al., Appl. Opt., 44, 5069 (2005)

Authors name: E. Förster, Institute of Optics and Quantum Electronics, Max-Wien-Platz 1, D-07743 Jena, Germany. E-mail: [email protected] HU1100099

X-ray generation by laser-cluster interaction C. Deiss1, E. Lamour2, C. Prigent2, J.P. Rozet2, D. Vernhet2 and J. Burgdörfer1 'Institute for Theoretical Physics, Vienna University of Technology, Vienna, Austria, EU 2INSP, Universités P. et M. Curie et D. Diderot, Paris, France, EU

The interaction of short and ultra-short intense laser pulses with clusters has become an important area of laser-matter research bridging the gap between gas-phase and solid-state processes. The observation of characteristic x-ray emission from laser-irradiated clusters suggests its potential as an x-ray source through a highly non-linear conversion of 1R radiation that combines advantages of both solid and gaseous targets. Recent experiments [1,2] found an unexpectedly low laser intensity threshold for characteristic x-ray production of 15 2 5 lth ~ 2,2xl0 Wcnr when irradiating argon clusters with a mean size ofN=2.8xl0 atoms with laser pulses of duration r=60 fs at A =800 nm. Since at those intensities direct laser field induced production of inner-shell vacancies can be ruled out, the origin of these vacancies is electron-impact ionization. Characteristic x-ray production can thus be viewed as a thermometer for hot electrons inside the cluster, as it tests the high energy tail of the electron energy distribution. For these laser intensities the ponderomotive energy associated with the quiver motion of a free electron in the field would be of the order of Up =130 eV, more than one order of magnitude below the energy threshold for K-shell electron-impact ionization of argon at approximately 3 keV. This observation raises questions as to the efficient heating mechanism for electrons in large clusters at such moderate intensities of short pulses. We propose elastic electron scattering at the core potential of cluster ions in the presence of the laser field as a highly efficient and very fast electron heating mechanism. Elastic backscattering at the atomic potential of the ions can flip the velocity vector of an electron, allowing it, with non-negligible probability, to remain synchronized with the alternating laser field vector. The electron will thus efficiently accumulate, rather than lose, momentum during subsequent laser half-cycles, thereby rapidly gaining kinetic energy well beyond the ponderomotive limit. In order to test the efficiency of this heating mechanism, we developed a Classical Trajectory Monte Carlo simulation to describe the dynamics of the electrons in the cluster [3,4], Our model takes into account the interaction of the electrons with the laser field, the build-up of an overall charge of the cluster due to electrons leaving the cluster (outer ionization), the resulting cluster expansion, polarization of the cluster due to collective electron motion, electron-impact ionization, and elastic scattering of the electrons by the ions inside the cluster. Our model results in a high-energy tail of the electron distribution being sufficient to produce K-shell vacancies. At moderate intensities, close to the x-ray production threshold, large-angle electron-ion scattering contributes efficiently to the heating of the electrons. We then find good quantitative agreement with the experimentally measured effective x-ray yields. Work supported by FWF (Austria).

[1] E. Lamour et al., Nucl. Instr. and Meth. B 235, 408 (2005). [2] C. Prigent, Ph.D. thesis, Paris, (2004) http://tel.ccsd.cnrs.fr/ [3] C. Deiss, N. Rohringer and J. Burgdörfer, Nucl. Instr. and Meth. B 235, 210 (2005). [4] C. Deiss et al., Phys. Rev. Lett. 96, 013203 (2006).

Cornelia Deiss, e-mail: [email protected] Cs^D HU1100100

Interaction of ultra-high intensity laser pulse with a mass limited targets A.A. Andreev1, J. Limpouch2, J. Psikal2, K.YulPlatonov1, S. Kawata3 1 Institute for Laser Physics, VSOI, Birzhevaya line 12, 193232 St Petersburg, Russia 2Czech Technical University in Prague, FNSPE, Brehova 7, 115 19 Praha 1, Czechia Department of Electrical and Electronic Engineering, Utsunomiya University, Japan

Ultra-high intensity laser pulses may be produced now via CPA scheme by using very short laser pulses of a relatively low energy. Interaction of such pulses with massive target is not very efficient as the energy delivered to charged particles spreads out quickly over large distances and it is redistributed between many secondary particles. One possibility to limit this undesirable energy spread is to use mass limited targets (MLT), for example droplets, big clusters or small foil sections. This is an intermediate regime in target dimensions between bulk solid and nanometer-size atomic cluster targets. A few experimental and theoretical studies have been carried out on laser absorption, fast particle generation and induced nuclear fusion reactions in the interaction of ultrashort laser pulses with MLT plasma. We investigate here laser interactions with MLT via 2D3V relativistic electromagnetic PIC simulations. We assume spherical droplet as a typical MLT. However, the sphere is represented in 2D simulations by an infinite cylinder irradiated uniformly along its length. We assume that MLT is fully ionized before main pulse interaction either due to insufficient laser contrast or due to a prepulse. For simplicity, we assume homogeneous plasma of high initial temperature. We analyze the interaction of relativistic laser pulses of various polarizations with targets of different shapes, such as a foil, quadrant and sphere. The mechanisms of laser absorption, electron and ion acceleration are clarified for different laser and target parameters. When laser interacts with the target front side, kinetic energy of electrons rises rapidly with fast oscillations in the kinetic and field energy, caused by electron oscillations in the laser field. Small energy oscillations, observed later, are caused by the electron motion back and forth through the droplet. Approximately 40% of laser energy is transferred to the kinetic energy of electrons and ions. When MLT is irradiated by ultra-high power laser pulse, the resulting plasma is strongly accelerated forward by the laser-induced ponderomotive force and its front side significantly compressed into a high density shock layer. The electrons in the shock layer are heated, and the plasma bunch then expands as a rocket. Thus, the forward acceleration of the high density region continues even after the laser pulse. The ion kinetic energy in this region can exceed tens of MeV at approximately solid density. For laser intensities above Coulomb threshold the efficiency of laser energy conversion into ion energy increases and the regime of direct plasma acceleration by light pressure may be reached. Since the plasma bunch is moving forward during the reflection, red-shift of the reflected light is observed. Twice higher maximum fast ion energy was found for droplet target compared to the standard thin foil target. In simulations of MLT including two different ion sorts, the observed maximum in the light ion distribution is caused by their additional acceleration in the electrostatic field of heavy ions. Parameters of this pike are determined by laser intensity and by the ion concentration ratio.

Presenting author'. Prof. Alexander Andreev, Institute for Laser Physics Vavilov State Optical Institute, Birzhevaya line 12 199034 St.Petersburg, Russia, [email protected] CmöT>

Production of collimated high-current ion beams by short-pulse lasers J. Badziak, S. Jablonski, S. Giowacz, P. Parys, and J. Wolowski Institute of Plasma Physics and Laser Microfusion, EURATOM Association, Warsaw, Poland

Ion beams driven by a short-pulse laser have potential to be applied in numerous fields of research as well as in medicine and technology. Some of the applications (e.g. accelerator technology, cancer therapy, particle physics) require high ion energies (tens of MeV or higher) and, possibly, a narrow energy spectrum of produced ions, while ion densities and currents of the beams can be moderate. On the other hand, in such applications as high energy-density physics (HEDP), fast ignition (FI) of inertial fusion, ion implantation or radioisotope production for PET, the ion energies up to several MeV are sufficient, but ion densities and currents (or current densities) should be very high. A recognized method of production of collimated, high-ion-energy beams is Target Normal Sheath Acceleration (TNSA) [1, 2], However, for the production of dense high-ion-current beams, Skin-Layer Ponderomotive Acceleration (SLPA) [3, 4] seems to be more promising method. In this lecture, basic properties of generation of high-ion-current beams by SLPA induced by a short (

[1 ] S. P. Hatchett et al., Phys. Plasmas 7,2076 (2000); S.C. Wilks et al., Phys. Plasma 8, 542 (2001). [2] M. Hegelich et al., Phys. Rev. Lett. 89, 085002 (2002); T.E. Cowan et al., Phys. Rev. Lett. 92, 204801 (2004). [3] J. Badziak, et al., Appl. Phys. Lett. 85, 3041 (2004); J. Badziak et al., Plasma Phys. Control. Fusion 46, B541 (2004). [4] J. Badziak, et at., Laser Part. Beams 23, 401 (2005).

HU1100101 CMol2>

Bubble regime of wake field acceleration with few cycle laser pulses Michael Geissler1, Jörg Schreiber1, Sergey Rykovanov1 ánd Jürgen Meyer-ter-Vehn1 1 Max-Planck Institut für Quantenoptik, Garching, Germany

Particle accelerators are one of the most important tools not only for basic science but also for many applications in medicine and technology. Over two decades particle acceleration with lasers was studied but beside the theoretical advantages over classic accelerators with comparable little success. Nevertheless the continuous improvements in laser technology resulted in a break though in laser driven accelerators in the last years. Based on theoretical predictions a new parameter regime for laser-electron acceleration was found, which is called bubble or blowout regime. Here a low emittance, highly charged, ultra-short electron pulse with a well-defined energy is generated during the interaction of a high power laser pulse in a gas. In this talk I will introduce this bubble regime and its characteristic features, the necessary laser parameter, and the possible tuning of the electron pulse properties. I will focus on few cycle laser pulses and descuss their advantages and disadvantages compared to longer pulses. Recent experiments done with 30-100fs pulses in this regime will also be analyzed revealing the strong nonlinear reshaping of the laserpuls which is the main reason for the observed shot- to-shot-fluctuation of the measured electron spectra. The presentation is based on animations from 3D-Simulations to illustrate the complicated highly non-linear processes.

Corresponding Author: Michael Geissler, [email protected]

HU1100102 HU1100103

Super-high frequency upshifting in the nonlinear interaction of laser pulse with breaking wake wave Alexander S. Pirozhkov*, Sergei V. Bulanov, Timur Zh. Esirkepov, Hiroyuki Daido, and Toshiki Tajima Advanced Photon Research Center, Kansai Photon Science Institute, Japan Atomic Energy Agency, 8-1 Umemidai, Kizu-cho, Soraku-gun, Kyoto 619-0215, Japan

The generation of coherent high-frequency radiation is the topic of great interest since the invention of lasers. Among the proposed schemes are the x-ray laser, free-electron laser, high-order harmonic generation in gases, relativistic harmonics from the solid targets, and so on. Recently, the relativistic frequency upshifting accompanied by the light intensification and pulse shortening was proposed using the Flying Mirror technique [1], According to the rela- tivity theory, the frequency of light pulse reflected at the relativistic mirror moving toward it, is upshifted by the factor —4}?. Here we describe new method of super-high frequency generation, using simultaneously the relativistic upshifting and harmonic generation, resulting in the net factor of where N is the harmonic number. When a relativistic-irradiance laser pulse ("driver", subscript "0") propagates in the underdense plasma, it creates a wake wave with the phase velocity equal to the group velocity of the driver pulse, which is close to the velocity of light c for a small plasma density n0. 2 U2 The gamma-factor \sy~(UQlajpe » 1, where

1. S. V. Bulanov, T. Zh. Esirkepov, and T. Tajima, Phys. Rev. Lett. 91, 085001 (2003). 2. V. A. Vshivkov, N. M. Naumova, F. Pegoraro, and S. V. Bulanov, Phys. Plasmas 5,2727 (1998). 3. A. S. Pirozhkov, S. V. Bulanov, T. Zh. Esirkepov, M. Mori, A. Sagisaka, and H. Daido, Phys. Lett. A 349, 256 - 263 (2006). 4. A. S. Pirozhkov, S. V. Bulanov, T. Zh. Esirkepov, M. Mori, A. Sagisaka, and H. Daido, Phys. Plasmas 13, 013107 (2006).

*pirozhkov.alexander@jaea. go.jp HU1100104

GeV electron beams from table-top laser-plasma accelerator using capillary waveguides Cs. Tóth1, B. Nagler1, K. Nakamura1, A.J. Gonsalves2, S.M/Hooker2, C.G.R. Geddes', C.B. Schroeder1, E. Esarey1, and W.P. Leemans1 1LOASIS Program, Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA, USA -Department of Physics, University of Oxford, Clarendon Laboratory, Oxford, UK

Conventional particle accelerators for radiation sources, high-energy physics, and other applications are typically limited to accelerating gradients -50 MV/m to avoid material breakdown, resulting in bulky, expensive machines. A new technology for generating intense energetic electron beams and synchronized femtosecond radiation sources is plasma acceleration using high-peak power, ultrashort-pulse, high energy lasers [1].

\ The physics, research status, and challenges of laser-plasma accelerators and future radiation sources based on these advanced particle accelerators will be discussed. The radiation pressure of an intense laser pulse drives a space charge wave in fully ionized plasma, producing acceleration gradients on the order of 100 GV/m and micron-wavelength accelerating structures for femtosecond beams. To drive such structures, short pulse lasers are used (40 fs, 40 TW, 1=1018-1019 W/cm2), so that the ponderomotive force resonantly drives the plasma wave 18 -3 (L|aSCT~ c/ft/p) in cold, low-density plasmas (Te ~ 10 eV, nc ~10 cm ). Structured plasmas (channels) are used to guide this drive pulse, maintaining the accelerating field beyond the laser diffraction range.

Electron beams of narrow energy spread and good emittance have been produced at several facilities [2-4] by extending the acceleration distance to match the dephasing length over which the particles outrun the wave. Recently, the acceleration distance has been extended again to cm-scale at LBNL, using channels in a capillary discharge, developed at University of Oxford [5], and resulting in energies up to 1 GeV. Challenges of applications of laser accelerators include control and reproducibility of the electron beam, scaling to higher energies, and detailed modeling to understand what optimizations are available. In particular, injection of particles into the wave must be accurately controlled, and shot to shot variation must be reduced.

References

[1] T. Tajima and J. M. Dawson, "Laser electron accelerator," Physical Review Letters, 43, 267, 1979. [2] C. G. R. Geddes, C. Toth, J. van Tilborg, E. Esarey, C. B. Schroeder, D. Bruhwiler, C." Nieter, J. Cary, and W. P. Leemans, "High-quality electron beams from a laser wake- field accelerator using plasma-channel guiding," Nature, 431, 538, 2004. [3] S. P. D. Mangles, C. D. Murphy, Z. Najmudin, A. G. R. Thomas, J. L. Collier, A. E. Dangor, E. J. Divall, P. S. Foster, J. G. Gallacher, C. J. Hooker, D. A. Jaroszynski, A. J. Langley, W. B. Mori, P. A. Norreys, F. S. Tsung, R. Viskup, B. R. Walton, and K. Kjushelnick, "Monoenergetic beams of relativistic electrons from intense laser-plasma interactions," Nature, 431, 535, 2004. [4] J. Faure, Y. Glinec, A. Pukhov, S. Kiselev, S. Gordienko, E. Lefebvre, J. P. Rousseau, F. Burgy, and V. Malka, "A laser-plasma accelerator producing monoenergetic electron beams," Nature, 431,541 2004. [5] A. Butler, D. J. Spence, and S. M. Hooker, "Guiding of High-Intensity Laser Pulses with a Hydrogen-Filled Capillary Discharge Waveguide," Phys. Rev. Lett. 89, 185003, 2002.

Corresponding author: Csaba Tóth, [email protected] Laser-plasma accelerators Victor Malka, A. Lifschitz, J. Faure, Y. Glinec LOA, ENSTA, X, CNRS, UMR 7639, 91761 Palaiseau, France.

The concepts of laser-plasma based accelerator and injector are discussed here. A two stage laser plasma accelerator design study for the production of a high-quality 3 GeV electron beam with low energy spread (1%) is proposed. New results demonstrating colliding laser pulses scheme will be also presented. These laser-produced particle beams have a number of interesting properties and could lend themselves to applications in many fields, including medicine (radiotherapy), chemistry (radiolysis), accelerator physics, and as a source for the production of y rays beams for non-destructive material inspection by radiography, or for future compact XFEL machines.

* Corresponding Author: Malka Victor, E-mail: [email protected]

HU1100105 Cmö

Direct evidence of electric fields and fast electron slowing down during propagation in high-intensity laser matter interaction D.Batani1,*, S.D.Baton2, M.Manclossi1,*, M.Koenig2, A. Benuzzi-Mounaix2, H. Popescu2, F.Amiranoff2, C.Rousseaux3, M.Borghesi4, C.Cecchetti4 1 Dipartimento di Fisica "G.Occhicilini", Universitr di Milano-Bicocca, Italy 2LUL1, Ecole Polytechnique, CNRS, Palaiseau, France 3Commissariat f l'Energie Atomique, Bruyéres-le-Chátel, France 4Queen s University Belfast, UK 5Universitr di Roma "La Sapienza ", Rome, Italy

Abstract We present the results of recent experiments performed at the LUL1 laboratory, using the 100 TW laser facility, on the study of the propagation of fast electrons in gas targets. Novel diagnostics have been implemented including chirped shadowgraphy and proton imaging. Proton images showed the presence of very strong fields in the gas, likely produced by charge separation. In turn, these imply a strong inhibition of propagation, and a slowing down of the fast electron cloud as it penetrates in the gas. Indeed chirped shadowgraphy images show a reduction in time of the velocity of the electron cloud from the initial value, of the order of a fraction of c, over a time scale of a few ps.

HU1100106 HU1100107

Propagation of high-current fast electron beam in a dielectric target O. Klimo1, A. Debayle2, V. T. Tikhonchuk2 'Czech Technical University in Prague, FNSPE, Brehova 7, 115 19 Praha 1, Czechia -Centre Lasers Intenses et Applications, CNRS-CEA-Universite Bordeaux 1, 33405 Talence Cedex, France

A relativistic electron beam with very high current density may be produced during the interaction of a short high intensity laser pulse with a solid target. In Fast Ignition approach to Inertial Confinement Fusion, such beam is supposed to heat a part of the precompressed DT fuel pellet to the conditions of an efficient ignition. For successful implementation of Fast Ignition understanding the propagation and energy deposition of the beam is crucial. A number of processes, mostly associated with the return current, are dissipating the energy of the beam or inhibiting its collimated transport, namely the filamentation, Weibel, two-stream or the recently proposed ionization instability. Ionization instability may develop in a solid dielectric target due to the dependence of the propagation velocity of the beam on the beam density. To study the propagation of high current electron beam in dielectric target, we use a one- dimensional relativistic electrostatic simulation code based on the Particle in Cell method. The code includes ionization processes in dielectric material and collisions of newly generated cold electrons. The current density of the relativistic electron beam used in this work is in the range 3-300 GA/cm2, while its length roughly corresponds to the beam, produced by a 40 fs laser pulse. Propagation of the beam in the polyethylene target is studied. The code is complemented by an analytical model, which is applicable to a wider range of beam parameters that are currently beyond our computational possibilities. When the head of the beam enters the plastic target, electric field grows rapidly in consequence of the charge separation and it starts to ionize atoms. In the maximum of the field, which is less than 10% of the atomic field, the density of new free electrons is two orders of magnitude higher than the beam density, which is enough for the current neutralization. Cold electrons are accelerated by the field, until they acquire enough energy for efficient collisional ionization. Then, the avalanche ionization starts and the further increase of cold electron density reduces plasma resistivity. The current of the rest of the electron beam is neutralized relatively easily. The electric field inside the beam is order of magnitude lower than in the ionization front and it drops to zero behind the beam. The evolution of the beam distribution along its propagation and the plasma produced inside the plastic target are studied. The propagation velocity of the ionization front is faster for higher beam densities in agreement with analytical model. The energy loss of the beam due to Ohmic heating influences its propagation significantly on the distance of order of tens of em. The losses are stronger for lower density beams and the average energy lost per beam electron is significantly higher than the collisional losses. For the higher beam density, the two-stream instability may develop behind the ionization front.

This work was partly funded by the Czech Ministry of Education, Youth and Sports project LC528. The support by the COST Office under project COST-STSM-P14-01494 is gratefully acknowledged. Presenting author: Ondrej KJimo, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Brehova 7, 115 19 Praha 1, Czech Republic, [email protected] HU1100108 Cjv^D

Plasma Physics with Intense VUV Radiation J. Meyer-ter-Vehn and A. Tronnier Max-Planck-Institute for Quantum Optics, D-85748 Garching, Germany

New intense VUV-FEL beams, presently becoming operational, as well as existing intense high harmonics sources make it possible to heat solid foils with photons of 10 - 100 eV energy and to study specifics of the interaction with hot dense matter. First transmission experiments with 38 eV photons performed in autumn 2005 at the VUV-FEL facility "FLASH" at DESY/Hamburg [1] have reached beam intensities up to 1014 W/cm2 heating metal foils to temperatures of 1 - 2 eV. Depending on focusing, intensities up to 1018 W/cm2 may become possible generating solid-density plasmas with temperatures up to 1 keV and multi-Gbar pressures [2, 3]. This would open unprecedented possibilities for high-precision dense-plasma studies and would be of great importance for the physics of inertial fusion [4], The major problem presently to achieve this ambitious goal is an experimental one: improved focusing techniques. Here we are concerned with theoretical modelling of VUV absorption in hot dense matter. In contrast to visible laser light, VUV radiation with frequencies beyond the plasma frequency u7p can propagate in the metal foils, though increasing ionization may abruptly block the propagation mode [5], At higher energies (> 100 eV), energy deposition in metals is dominated by bound-free photo-ionization processes. In the regime 10 - 100 eV, however, considered here, collisional absorption mediated by inverse bremsstrahlung of conduction electrons still plays a major role. It turns out that VUV collisional absorption is quite different from the well-known optical laser absorption [6], mainly because the photon energy exceeds the Fermi energy of metals, and target electrons are to be considered as "slow" in the relevant Coulomb collisions. The corresponding regime of "slow" electrons in radiative Coulomb collisions has been considered recently by Krainov [7, 8]. Here we use his results to model the VUV absorption coefficients. Results are compared with the recent DESY experiments.

References:

[1] http://www-hasylab.desy.de/ [2] A. Krenz, Transport und Absorption von intensiven XUV-Strahlen in dichten Plasma- Schichten, Diplomarbeit, TU München, 2003. [3] J. Meyer-ter-Vehn, Dense Plasma Physics Studied With FELs, Proceedigs IFSA'2003, Monterey, Sept. 7-12, 2003, Am. Nucl. Society, La Grange, 111. USA, 2004; pp.912-16. [4] S. Atzeni and J. Meyer-ter-Vehn, The Physics of Inertial Fusion: Beam Plasma Interaction, Hydrodynamics, Hot Dense Matter (Clarendon Press, Oxford, 2004). [5] A. Krenz and J. Meyer-ter-Vehn, Dense VUV-heating of plasma layers and their use as ultrafast switches, Eur. Phys. J. D, 36, 199-202 (2005). [6] K. Eidmann, J. Meyer-ter-Vehn, Th. Schlegel, S. Hueller, Hydrodynamics simulation of subpicosecond laser interaction with solid-density matter. Phys. Review E62, 1202 (2000). [7] V.P. Krainov, Inverse stimulated bremsstrahlung of slow electrons under Coulomb scattering, J. Phys. B: Mol. Opt. Phys., 33 (2000). [8] V.P. Krainov, Absorption of Electromagnetic Energy by Slow Electrons under Scatterinmg from Coulomb Centers. JETP 92, 1109 (2001). Statistical model of radiation damage within an atomic cluster irradiated by VUV photons from FEL Beata Ziaja'.2, A. R. B. de Castro1-3, E. Weckert1 and T. Moeller4 'HASYLAB, DESY Hamburg, Germany; '/NP, Krakow, Poland; 3LNLS, Sao Paulo, Brasil; 4TU, Berlin, Germany

Boltzmann equations are applied for modelling the radiation damage in samples irradiated by photons emitted from free electron laser (FEL).

This statistical approach is used to model the evolution of a spherically symmetric xenon cluster consisting of ~ 1000 atoms irradiated with FEL photons at VUV energies. Simulation parameters follow those set in the first cluster experiments performed at FLASH at DESY HAMBURG. Predictions obtained with this theoretical model are then compared to the experimental data.

The results obtained demonstrate the potential of the Boltzmann method for describing the complex and non-equilibrium dynamics of samples exposed to FEL radiation. In particular, this approach work also well for large samples, for which the standard simulation methods become inefficient.

HU1100109 CmoTO)

Astra-TAI Facility for Ultrafast Time-Resolved Science IC Edmond Turcu Central Laser Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX 11 OQX, UK E-mail address: [email protected]

Abstract A new, ten femtosecond pulsed laser system has been developed for ultrafast time-resolved science experiments at the Astra laser facility. The 1 Ofs pulses are generated by a hollow-fibre bandwidth-expander followed by a chirped mirror compressor. The Astra Target Area One (TA1) Facility now provides two laser beam configurations: 1kHz repetition rate with lOfs, 0.3mJ pulses, or 10 Hz repetition rate with lOfs, 0.5mJ probe pulses and 35fs, 15mJ synchronized pump pulses. We will start shortly to further upgrade Astra TA1 to a sub-ten femtosecond time-resolved science facility which is planned to provide three ultrafast, synchronized laser beam-lines with independently adjustable delay between them: (Beam-1) 7fs, 'few cycle' 1R laser pulse with carrier envelope phase (CEP) control; (Beam-2) 7fs, XUV pulse containing high harmonics of Beam-1, with photon energies from lOeV - 300 eV. The XUV radiation will be spectrally filtered in a pulse-duration-preserving monochromator; (Beain-3) 30fs - lOOfs, laser pulse, tuneable from UV (190nm) to mid 1R (20,000nm). We also plan to provide interaction stations for ultrafast time-resolved: material science, surface science and atomic and molecular science, as well as state-of the-art diagnostics for the above stations.

Figure 1. Image of the ten-femtosecond hollow-fibre pulse compressor in the Astra TA1 facility. The lOfs pulse can be split, in an interferometer, into two synchronized pulses, with variable delay between them, to conduct ultrafast pump-and-probe experiments. An interaction station can be seen to the right of the compressor table.

HU1100110 Applications of multi-millijoule soft X-ray lasers in dense plasma physics B. Rus et al. Department of X-ray Lasers, Institute of Physics/ PALS Centre, Prague 8, Czech Republic

We will present a review of the program of development and applications of soft X-ray lasers, carried out at the PALS Centre. These applications benefit from currently the most energetic plasma-based laboratory X-ray laser, based on double-pass amplification in Ne-like zinc amplifier and emitting up to 10-mJ pulses at the wavelength of 21.2 nm. We will shortly describe the pumping techniques used to produce this laser, and will outline prospect for further boosting its output. Most of the presentation will be devoted to the application experiments recently undertaken at PALS in numerous international collaborations. These applications include probing of plasmas produced by 1R laser pulses and high-energy-density-in-matter (HEDM) experiments. We will present results of precise measurements of ablation rates of thin foils driven by intensities of about 2x 1014 Wcnr2, and of probing of columns of plasmas suitable as advanced X-ray amplifiers. We will further show recent results of measurements of transmission of focused soft X-ray radiation at intensities up to 1013 Went"2 in thin foils, and will discuss prospects for probing high density plasmas by X-ray laser Thomson scattering.

HU1100111 HU1100112 CMol2>

High-energy few-cycle pulse compression through self-channeling in gases C. Hauri', M. Merano', A. Trisorio', F. Canova1, L. Canova', R. Lopez-Martens' T. Ruchon2, A. Engquist2, K. Varjú2. E. Gustafsson2, A. L'Huillier2, E. Power3 'Laboratoire d'Optique AppHquée, ENSTA-Ecole Polytechnique, F-9I76I Palaiseau Cedex, France 2 Department of Physics, Lund Institute of Technology, P.O. Box 118, SE-22100 Lund, Sweden 3Centerfor Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Blvd, Ann Arbor, Ml 48109, USA

Nonlinear spectral broadening of femtosecond optical pulses by intense propagation in a Kerr medium followed by temporal compression constitutes the Holy Grail for ultrafast science since it allows the generation of intense few-cycle optical transients from longer pulses provided by now commercially available femtosecond lasers. Tremendous progress in high-field and attosecond physics achieved in recent years has triggered the need for efficient pulse compression schemes producing few-cycle pulses beyond the mJ level. We studied a novel pulse compression scheme based on self-channeling in gases1'2, which promises to overcome the energy constraints of hollow-core fiber compression techniques3. Fundamentally, self-channeling at high laser powers in gases occurs when the self-focusing effect in the gas is balanced through the dispersion induced by the inhomogeneous refractive index resulting from optically-induced ionization. The high nonlinearity of the ionization process poses great technical challenges when trying to scale this pulse compression scheme to higher energies input energies. Light channels are known to be unstable under small fluctuations of the trapped field that can lead to temporal and spatial beam breakup, usually resulting in the generation of spectrally broad but uncompressible pulses. Here we present experimental results on high-energy pulse compression of self-channeled 40-fs pulses in pressure-gas cells. In the first experiment, performed at the Lund Laser Center in Sweden, we identified a particular self-channeling regime at lower pulse energies (0.8 mJ), in which the ultrashort pulses are generated with negative group delay dispersion (GDD) such that they can be readily compressed down to near 10-fs through simple material dispersion. Pulse compression is efficient (70%) and exhibits exceptional spatial and temporal beam stability. In a second experiment, performed at the LOA-Palaiseau in France, we successfully scaled this pulse compression regime to the multi-mJ level. In this case, temporally clean 10-fs pulses with energies up to 1.8 mJ could be generated through self-channeling of 3.5 mJ, 40-fs pulses. Again, the spectrally broadened pulses are seen to carry large negative chirps and the shortest measured pulse duration of 9.5-fs was achieved by inserting more than 1 cm of glass in order to compensate for the negative GDD. Single-shot measurements show the exceptional shot- to-shot stability of this pulse compression scheme. In conclusion, we demonstrate a stable nonlinear pulse compression technique based on self- channeling of intense 40-fs pulses in gases, in which ultrashort pulses are efficiently generated with unexpected large negative chirp. The strongly pre-compensated spectral phase characteristics of such few-cycle pulses makes them a practical driving source for further high-field applications since the shortest pulse durations can be achieved on target by simple propagation through bulk material (e.g. vacuum window). Simulations involving the solution to the nonlinear propagation equation are underway in order to understand this unexpected pulse compression regime and to find optimal conditions for further scaling in energy. 1. Hauri, C.P., et al., Generation of intense, carrier-envelope phase-locked few-cycle laser pulses through filamentation. Appl. Phys. B 79, 673 (2004). 2. Nisoli, M., et al., A novel high-energy pulse compression system: generation of multigi- gawatt sub-5-fs pulses. Appl. Phys. B 65, 189 (1997). 3. G. Stibenz, N.Zhavoronkov, G. Steinmeyer, Self-compression of millijoule pulses to 7.8 fs duration in a white-light filament. Opt. Lett. 31, 274 (2006). CmölD HU1100113

Hybrid Ti:Sapphire / KrF laser facility GARPUN for combined subpicosecond/ nanosecond laser-matter interaction studies V.D. Zvorykinl '*, N. V. Didenko2, A.A. Ionin1, A.V. Konyashchenko1, A.O. Levchenko1, O.N. Krokhin1, G.A. Mesyats1, A.O. Mavritskii2, A.G. Molchanov1, M.A. Rorulev1, L.V. Seleznev1, D.V. Sinitsyn1, S.Y. Tenyakov2, N.N. Ustinovskii1 'P.N. Lebedev Physical Institute of Russian Academy of Sciences, Leninsky pi: 53, 119991 Moscow, Russia 2Avesta Project Ltd., Solnechnaya st. 12, 142190 Troitsk, Moscow region, Russia

Hybrid laser facility consisting of Ti: Sapphire front end, 3a> converter, and e-beam- pumped large-aperture KrF amplifiers is under construction to generate combined subpicosecond/ nanosecond pulses in UV spectral range at 248-nm wavelength. This is a part of the Petawatt excimer laser project started at P.N. Lebedev Physical Institute [1], In comparison with commonly used solid-state chirped-pulse amplifiers (CPA), KrF amplifiers have following advantages: (i) low-density gaseous matter with three orders of magnitude lower non-linear refraction index has a small value of B-integral and negligible pulse distortion; (ii) short radiation lifetime rt. =6 ns of the upper laser level of KrF(B-X) transition (with accounting for collisions rc ~2 ns), that means the population inversion is recovered each 2 ns during the pumping time, which is typically rp >100 ns for technical reasons. Thus, it might be possible eliminating of very costly large-aperture compressor gratings and to amplify both short ts/i « tc and long T/ang> rc pulses in the same amplifiers, as a short pulse does not affect the gain during the most of pumping. This gives a unique opportunity for realization of fast-ignition scheme in Inertial Confinement Fusion using large-scale KrF drivers [2], The Ti:Sapphire front end "Start 248M" currently operates with the following parameters: rep rate 10 Hz, pulse energy and duration at fundamental wavelength (744 nm) > 8 mJ and < 60 fs, at 3a> (248 nm) > 0.5 mJ and < 65 fs, energy reproducibility (rms) < 3 % (744 nm) and < 4 % (248 nm). It consists of Kerr lens mode-locked master oscillator (<30 fs, 80 MHz, 150 mW, wavelength centered at 740 nm) pumped by leu diode-pumped CW Finesse 4W Nd:YAG laser (3.5 W, 532 nm), all reflective-optics stretcher, which stretches pulses up to 200 ps, successive regenerative amplifier (10 Hz, > 0.4 mJ, 740 nm) and multi-pass amplifier (10 Hz, > 15 mJ, 740 nm), both pumped by 2m pulsed Lotis LS-2134 Nd:YAG laser (10 Hz, 10 ns, 532 nm) with distributed energies of 5 and 70 mJ, two-gratings compressor, and 3u converter with two BBO crystals and total efficiency 8%. EMG 150MSC Lambda Physik KrF laser is used afterwards to generate ns pulses and to amplify fs pulses in its two separate discharge chambers. Two e-beam-pumped KrF amplifiers Berdysh and GARPUN with active volumes 10x10x100 and 16x18x100 cm3 are intend- ed for amplification of both fs and ns pulses, as well as their combination. Preliminary numerical simulations predict 1.5 J, subpicosecond pulses combined with up to 100 J, nanosecond pulses.

1. V.D. Zvorykin, A.A. Ionin, V.F. Losev et al., Paper was presented at 3 Int. Cortf. "Superstrong Fields in Plasmas ", Varenna, Italy, September 19-24, 2005. 2. V.D. Zvorykin, I.G. Lebo, V.B. Rozanov, Bull, of Lebedev Phys. Inst., No. 9-10, 20-23 (1997)

*Vladimir D. Zvorykin, e-mail: [email protected] HU1100114 CMÖÍ4>

A bandwidth independent linear method for detection of carrier envelope phase drift M. Görbe1, K. Osvay1'2 department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary 2Max-Born-lnstitut für Nichtlineare Optik und Kurzzeitspektroskopie, Berlin, Germany

Most of the femtosecond-scale physical phenomena can be experimentally investigated by using carrier-envelope phase (CEP) stabilized laser pulses only [1-2]. The usual method of CEP stabilization [3-4] requires laser pulses with a bandwidth of one octave broad at least. If the spectrum of the fundamental pulse itself is not sufficiently broad, then its bandwidth has to be broadened by use of any nonlinear method [5], Spectrally and spatially resolved interferometry (SSRI) has been proven to be a powerful technique for dispersion measurement of various materials and optical elements [6-7]. It typically consists of a two-beam interferometer equipped with an imaging spectrograph. The interference pattern is imaged onto the input slit of the spectrograph, so that spatially (along the slit) and spectrally resolved interference fringes are formed on the 2D detector (CCD camera) inserted at the output plane of the spectrograph. In this paper we show that the visibility of the spectrally and spatially resolved interference fringes depends strongly on the CEP drift of subsequent pulses from a pulse train. When the pulses are CEP stabilized then the visibility has a definite extremum. To introduce the operation principle, let's assume a black box in the sample arm of the interferometer illuminated by train of CEP-stabilized laser pulses. This imaginary black box would change only the CEP of the subsequent pulses by txp but leaves their dispersion relative to the reference pulse, i.e. the pulse propagating in the other arm of the interferometer, unchanged. The spatial position of the interference fringes depends on /Sip. If the subsequent fringes are formed by pulses with different CEP, the spatial position of each interference fringe changes. The detector, i.e. the CCD chip of the imaging spectrograph is slow, so that it actually captures many subsequent interference patterns, on top of each other. As a result, the visibility of the resulted and captured interference fringes is substantially degraded. If one uses unstabilized femtosecond pulses from an oscillator, then the above described situation, when certain number of pulses with different CEP interferes with a given pulse, can be experimentally implemented by inserting a ring resonator inside the sample arm of the interferometer. So the reference pulse interferes with the remnants of all the previous (sample) pulses of the pulse train circulating in the ring resonator, each having the inherited CEP drift from the oscillator. Our extended simulations show, that the visibility of the interference fringes depends on the measure of CEP drift as well as on the number of interfering pulses determined by the finesse of the ring resonator. This feature can be used not only for an easy detection of CEP fluctuation but also for CEP stabilization of the pulse train itself. Moreover, please note that this method is inherently independent on the bandwidth of the pulses to be CEP stabilized. This work was supported by OTKA under grant T047078 and NKFP 1/00007/2005.

1. Hentschel, et. al., Nature 414, 509 (2001) 2. R. K. Shelton et al., Science 293, 1286 (2001) 3. G.G. Paulus et. al., Nature 414, 182 (2001) 4. A. Baltuska et al., Nature 421, 611 (2003) 5. F.X.Kártner (ed.), Few-cycle laser pulse generation and its applications, Springer, 2004 6. A. P. Kovács, K. Osvay, Z. Bor, R. Szipőcs, Opt. Lett. 20, 788 (1995) 7. K. Osvay, P. Dombi, A. P. Kovács, Z. Bor, Appl. Phys. B 75, 649 (2002)

Corresponding author: Karoly Osvay, [email protected] HU1100115 CjuD

Linear and Non-Linear Carrier-Envelope Phase Difference Effects in Interactions of Ultra-Short Laser Pulses with a Metal Nano-Layer Sándor Varró Research Institute for Solid State Physics and Optics Letters: H-1525 Budapest, POBox 49, Hungary Phone: +36-1-392-2635, Fax: +36-1-392-2215 E-mail: [email protected]

On the, basis of classical electrodynamics the reflection and transmission of an ultra-short laser pulse impinging on a metal nano-layer have been analysed. The thickness of the layer was assumed to be of the order of 2-10 nm, and the metallic electrons were represented by a surface current density at the plane boundary of a dielectric substrate. It has been shown that in the scattered fields a non-oscillatory wake-field appears following the main pulse with an exponential decay and with a definite sign of the electric and magnetic fields. The characteristic time of these wake-fields is inversely proportional to the square of the plasma frequency and to the thickness of the metal nano-layer, and can be of order or larger then the original pulse duration. The magnitude of these wake-fields is proportional with the incoming field strength - so this is a linear effect - and the definite sign of them is governed by the cosine of the carrier-envelope phase difference of the incoming ultrashort laser pulse. As a consequence, when we let such a wake-field excite the electrons of a secondary target - say a plasma, a metal surface or a gas - we obtain 100 percent modulation depth in the electron signal in a given direction. This scheeme can perhaps serve as a basis for the construction of a robust linear carrier-envelope phase difference meter. At relativistic laser intensities the target becomes a plasma layer generated, e. g. by the ris- ing part of the incoming laser pulse. An approximate analytic solution has been given for the system of the coupled Maxwell-Lorentz equations describing the dynamics of the surface current (representing the plasma electrons) and the composite radiation field. With the help of these solutions the Fourier components of the reflected and transmitted radiation have been calculated. The nonlinearities stemming from the relativistic kinematics lead to the appearance of higher-order harmonics in the scattered spectra. In general, the harmonic peaks are down-shifted due to the presence of the intensity-dependent factors of order of 15-65 per cent in case of an incoming field of intensity 2* 10l9W/cm2. This phenomenon is analogous to the famous intensity-dependent frequency shift appearing in the high-intensity Compton scattering on a single electron. In our analysis particular attention has been paid to the role of the carrier-envelope phase difference of the incoming few-cycle laser pulse. For instance the 4th harmonic peak strongly depends on the carrier-envelope phase difference with a modulation being more than 20 percent. It is also shown that the spectrum has a long tail where the heights of the peaks vary practically within one order of magnitude in the frequency range considered. By Fourier synthesising the components from this "plateau" region of the higher-harmonic spectrum, attosecond pulses have been obtained. HU1100116

Intense harmonic generation from various ablation media T. Ozaki and L. Elouga Bom1' M. Suzuki and H. Kuroda2> R. A. Ganeev3 1INRS-EMT, Université du Québec, 1650 Lione- Boulet, Varennes, Québec J3X 1S2 Canada ozaki@inrs-emt. uquebec. ca 2ISSP, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 Japan 3NPO Akadempribor, Academy of Sciences of Uzbekistan, Akademgorodok, Tashkent 700125 Uzbekistan

Abstract: Systematic investigation of ablation harmonics are performed for various targets, using the 40 mj, 25 fs output from the Advanced Laser Light Source. Optimum pre-pulse and main pulse conditions for ablation harmonics are studied.

High-order harmonic generation (HHG) is a unique source of coherent extreme ultraviolet (XUV) radiation, which can produce soft x-rays within the spectral "water-window" (between 2.3 and 4.4 nm) [I], and ultimately short pulses with attosecond duration [2], However, the intensity of present-day harmonics is still low, and serious applications will need an increase of the conversion efficiency. Instead of using gas media, one can also use ablation material, produced on solid targets using a low-intensity prepulse [3], as the nonlinear medium to generate high-order harmonics. Recently, we have successfully demonstrated the generation of up to the 63rd harmonic (i=12.6 nm) of a Ti:sapphire laser radiation using boron ablation [4], and a strong enhancement in the intensity of the 13lh harmonic from indium ablation [5], These harmonics were generated with a modest laser (10 mJ, 150 fs) and with the pre-pulse to main pulse energy ratio constant. In this paper, we perform systematic investigations of ablation harmonics, using the 200 mj, 30 fs Ti:sapphire beam line of the Canadian Advanced Laser Light Source (ALLS) facility. ALLS allows studying ablation harmonics over wider experimental parameters, and with independent control over the pre-pulse and main pulse energies. The 10 Hz, 200 mJ Ti:sapphire beam line of ALLS is divided into two beams. Each beam has its own energy control system, which allows independent control over the energy of each beam. One of the beams is used as a pre-pulse for creating ablation, which is focused onto the solid target without pulse compression, with pulse duration of 200 ps. The second beam is used as the main pulse for harmonic generation. The main pulse is delayed in time relative to the pre-pulse by propagating through an optical delay line, and then sent through a pulse compressor. The compressed pulse duration have typical pulse duration of 30 fs FWHM, which is then focused onto the ablation medium using MgF2 lens (f = 680 mm). The high-order harmonics were spectrally resolved using a flat-field grazing-incidence XUV spectrometer with a Hitachi 1200-grooves/mm grating. The XUV spectrum was detected by a microchannel plate with phosphor screen and recorded by a CCD camera. Ablation harmonic experiments were performed with silver and indium targets. We selected silver because of its high conversion efficiency, and indium for its peculiar intensity enhancement effects of the 131,1 harmonics [6], Due to the high intensities of the ablation harmonics, all harmonic spectra were obtained in a single shot. Experiments reveal that the pre-pulse condition for maximum harmonic generation is distinctly different for the two targets. Hydrodynamic simulations using the HYADES code [6] show that the high density of the ablation medium results in strong absorption of the generated harmonics. Therefore, the trade-off between high harmonic efficiency and high absorption is especially important in the present scheme, which can change significantly with the pre-plasma condition. Results with indium targets also reveal a distinct change in the ratio between the 13th and 15th harmonic intensity when varying the main pump intensity. This phenomenon is attributed to the change in the resonance conditions of the 13lh harmonic with a strong radiative transition of the In+ ion, due to the AC-Stark effect. We will also present new results on ablation harmonics using tin targets.

References [1] C. Speilmann eta/., Science 278, 661 (1997). [2] M. Hentschel et al., Nature 414, 509 (2001). [3] Y. Akiyama et al., Phys. Rev. Lett. 69, 2176 (1992). [4] R. A. Ganeev et al., Opt. Lett. 30, 768 (2005). [5] R. A. Ganeev et al., to be published in Opt. Lett. (2006). [6] J. T. Larsen and S. M. Lane, J. Quant. Spectrosc. Radiat. Transfer, 51, 179 (1994). CtuD

KeV Harmonics in the Relativistic Limit Matt Zepf1*, B.Dromey1, A.Gopal2, K.Lancaster2,M.S.Wei2, K.Krushelnick2, M. Tatarakis3, S.Moustaizis4, R.Kodama5, M.Tampo5, C.Stoeckl6, R.Clarke7, H.Habara7, D. Neely7, S. Karsch7, R Norreys7 'Department of Physics and Astronomy, Queen's University Belfast BT7 INN, UK 2Blackett Laboratory, Imperial College, London SW7 2BZ, UK 3 Department of Electronics, Technological Ed. Institute o]Crete, 73133, Chania, Greece 4 Technical University of Crete, Institute of Matter Struct. & Laser Phys. Chania, Greece 5ILE University of Osaka, Osaka, Japan 6Laboratory for Laser Energetics, University of Rochester, Rochester, New York, USA 7 Central Laser Facility, Rutherford Appleton Laboratoty, Chilton, Didcot OX 11 OQX, UK

High harmonic emission from Laser - solid target experiments have been studied using the Vulcan PW laser(2). Using high contrast (> 1011:1) laserpulses with a peak intensity of 5 1020 Wcnr2 on target harmonics up the to 3.2 keV photon energy have been observed to be emitted into a specular cone. The conversion efficiency of the harmonics up to -2.5 keV has been found to follow the power-law scaling as ?;n=n"P with p~2.5±2. This is in good agreement with the relativistic scaling predicted by PIC simulations (3) and analytical theory. For the first time the limits of the power-law scaling have been investigated and an intensity dependent exponential roll-over is observed in the at photon energies >3 keV.

[1] P. Norreys et al, PRL, 76, 1832, 1996 [2] To be published, Nature Physics, July 2006 [3] S. Gordienko et al, PRL 93, 115002, 2004

* Corresponding Author: M. Zepf, [email protected]

HU1100117 Relativistic plasma control T. Baeva1, S. Gordienko2, A. Pukhov1 'Institut fiir Theoretische Physik I, Heinrich-Heine-Universitat Düsseldorf D-40225 Germany 2L. D. Landau Institute for Theoretical Physics, 1Moscow; Russia

To describe the high harmonic generation at plasma surfaces in the relativistic regime, the concept of apparent reflection point (ARP) is introduced. The relativistic dynamics of the ARP completely defines the generation of high harmonics and attosecond pulses. Managing the laser polarization, one can efficiently control the ARP dynamics, e.g. to gate a single (sub) attosecond pulse out of the short pulse train generated by a multi-cycle driver. This relativistic control is demonstrated numerically by PIC simulations.

""Corresponding Author: Teodora Baeva, [email protected]

HU1100118 Intense attosecond pulse source for pump-probe experiments G. D. Tsakiris, R. Hörlein, Y. Nomura, M. Geissler, K. Eidmann, J. Meyer-ter-Vehn, F. Krausz Max-Planck-lnslitut fiir Quantenoptik, Hans-Kopfermcmn-Str. /, D-85748 Garching, Germany

The advent of attosecond pulse generation has had a tremendous impact on the temporal measurement technology. It has provided the means of temporally resolving dynamic processes evolving at atomic time scales. The technique for the attosecond pulse generation relies on the production of phase-locked harmonics in a non-linear medium using short laser pulses. A number of attosecond spectroscopic measurements have been performed using attosecond sources based on high-harmonic generation in atomic gases. The scope of experiments that can be performed with this source is rather limited though because of the low number of photons available. Since the first observation of harmonic generation from solid targets using a tabletop laser system it became apparent that the interaction of an intense laser pulse with an overdense plasma constitutes an alternative route for the efficient production of phase- locked harmonics. Given the rapid technological advancements in laser technology, tabletop lasers based on the Optical Parametric Chirp Pulse Amplification (OPCPA) technique delivering several tens of TW power with kHz repetition rate appear to be within our reach. Motivated by these prospects, we have performed a series of simulations using the 1-D particle-in-cell (PIC) code LPIC. The results indicate that it is quite feasible that surface harmonics generated at laser intensities of I020 W/cm2 can produce a train of or even single attosecond pulses in the 20 - 70 eV spectral range with duration of ~80 as and efficiency of a few percent. More elaborate simulations using a 3D-PIC code not only corroborate these findings but also show that the XUV light reflected from the few-cycle-driven relativistic surface possess an excellent spatial coherence. The prospects of developing a source of intense attosecond XUV pulses using this method will be discussed on the basis of simulation and experimental results. The availability of such a source would allow the extension of the pump-probe femtosecond techniques to the extreme ultra-violet (XUV) and soft x-ray (SXR) regime, thus opening the way to real-time observation of a wide range of fast evolving phenomena in atomic, molecular and plasma physics.

HU1100119 HU1100120

Using shortwave infrared few-cycle pulses for generation of keV harmonics and attosecond pulses Vladislav S. Yakovlev,' Valer Tosa,2 and Ferenc Krausz' 'Department of Physics, Ludwig-Maximihans-Universitát München, Am Coulombwall I, D-85748 Garching, Germany. - National Institute for Research and Development of Isotopic and Molecular Technologies, P.O.Box 700, 3400 Cluj-Napoca, Rumania

Generation of kiloelectronvolt coherent high-harmonic radiation in a table-top system has been demonstrated in recent experiments [1], which exploited intense few-cycle light pulses with the central wavelength A0 = 0.8 /um. However, the low conversion efficiency of such sources limits their applicability. We show that the conversion efficiency can be increased by orders of magni-tude, if high harmonics are generated by few-cycle pulses with a longer wavelength, which are available from modern optical parametric chirped-pulse amplification (OPCPA) systems [2], The efficiency of HHG is determined by two factors: the strength of the single-atom dipole response and the phase-matching conditions. The former factor is limited [3] by the depletion of the atomic ground state, which leads to an exponential decrease in the single- atom dipole response with respect to the photon energy. A proper analysis of the role of phase-matching is only possi-ble by numerical solution of propagation equations, which we perform using a non-adiabatic 3D model [4, 5], We compare harmonics generated by conventional A() = 0.8 pm pulses with har-monics generated by A0 = 2.1 pm pulses under conditions that will be achievable in near-future experiments. We prove that even if the single- atom dipole response is significantly weaker in the former case, significantly higher intensities of propagated harmonic field can be achieved due to an increased coherence length. We also demonstrate that shorter attosecond pulses can be generated by filtering out the same spectral region from the harmonic plateau, if the harmonics are generated by a laser field with a longer wavelength.

[1] J. Seres, et. al. Nature, v. 433, 596 (2005) [2] T. Fuji et. al. Optics Letters, v. 31, 1103 (2006). [3] A. Gordon, F. X. Kartner, Optics Express, v. 13, 2941 (2005). [4] V. Tosa, et. al. Phys. Rev. A, v. 71, 063807 (2005). [5] N. Milosevic, A. Scrinzi, T. Brabec. Phys. Rev. Lett., v. 88, 093905 (2002).

""Electronic address: [email protected] Attosecond time-resolved spectroscopy of electron correlation in excited states Th. Mercouris1, Y. Komninos' and C. A. Nicolaides1'2 1 Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vasileos Constantinou Avenue, Athens, 11635 Greece 2Physics Department, National Technical University, Athens, Greece

By solving, from first principles, the time-dependent Schrödinger equation, we have examined quantitatively two general scenarios of pump-probe attosecond time-resolved spectroscopy of electron correlation in excited states. Specifically, the following schemes were investigated. 1) Two laser femtosecond pulses excite strongly correlated doubly excited configurations (DECs) of He, Be-like N+3 and of Al1'2 [and unpublished results]. The time-dependent coefficients of these DECs provide a "real-time picture", with quantitative validity, of the "motion" of electrons, as their oscillatory and dissipative (into the continuous spectrum) mixing takes place. Due to the large strength of electron correlation, the duration of this mixing is in the attosecond scale. For one of the states involved in the excitation-correlation scheme, the [Ne]3p3 2P° resonance state of Al, computed here for the first time, its width is calculated from a previously published energy-dependent golden rule-type formula and it is used as the imaginary part of a complex energy. The basic wavefunction characteristics of these doubly excited target states, as revealed by the time-dependent configurational mixing resulting from electron correlation, can in principle be observed in (de)excitation to other states using hypershort pulses as probes. We shall give a theoretical treatment and simple analytical for- mulas that could be used in a future experiment. 2) Along the lines of the recently discussed problem of "time resolved Fano resonances"^, we will show how the challenging phenomenological results3 can be obtained ab initio both numerically and analytically for the simple and rather "clean" spectrum of the doubly excited states (DES) of He. In addition, we shall provide numerical results, from first principles, for the more intriguing problem of simultaneous creation and decay of an inner hole state. Specifically, using attosecond pulses of high frequencies, we have produced results for the creation of a 2s-hole state in the Al atom and for its simultaneous very rapid decay, (life time ~ 6 fs), into several continua, according to the following excitation/decay scheme:

' (Is 2s"2p 3sJ fcd) P yp and i i, z I.- .. autoionization dccav , ; > : u > (Is 2s2p 3s 3p) P f.p =—>CIs 2s 2p 3s s;d) P sp

1 C. A. Nicolaides, Th. Mercouris and Y. Komninos, J. Phys. B 35, L271 (2002). 2 Th. Mercouris, Y. Komninos and C. A. Nicolaides, Phys. Rev. A 69, 032502 (2004). 3 M. Wickenhauser, J. Burgdörfer, F. Kraucz and M. Drescher, Phys. Rev. Lett. 94, 023002 (2005).

HU1100121 HU1100122 CjüD

High-order harmonics generation from overdense plasmas F.Quere', C.Thaury1, P.Monot1, Ph. Martin', J-P.Geindre2, P.Audebert2, R.Marjoribanks' 'Service des Photons, A tomes et Molecules (DSM/DRECA M), CEA 2Laboratoire pour L 'Utilisation des Lasers Intenses, CEA/CNRS/Ecole polytechnique 3Physics Department, University of Toronto, Canada

When an intense laser beam reflects on an overdense plasma generated on a solid target, high-order harmonics of the incident laser frequency are observed in the reflected beam (see [1] and ref. therein). This process provides a way to produce XUV femtosecond and attosecond pulses in the range from ultrafast ultraintense lasers. Studying the mechanisms responsible for this harmonic emission is also of strong fundamental interest: just as HHG in gases has been instrumental in providing a comprehensive understanding of basic intense laser-atom interactions, HHG from solid-density plasmas is likely to become a unique tool to investigate many key features of laser-plasma interactions at high intensities.

We will present both experimental (see figure) and theoretical evidence that two mechanisms contribute to this harmonic emission : - Coherent Wake Emission [2] : in this process, harmonics are emitted by plasma oscillations in the overdense plasma, triggered in the wake of jets of Brunei electrons [3] generated by the laser field. - The relativistic oscillating mirror [4] : in this process, the intense laser field drives a relativistic oscillation of the plasma surface, which in turn gives rise to a periodic phase modulation of the reflected beam, and hence to the generation of harmonics of the incident frequency.

L _ j CWE ROM A 1=100 uni i; 'ill. 1 Ui A z=200 Mm | H15 12 14 16 1 8 20 22 24 I larmonic order

Left graph : experimental harmonic spectrum from a polypropylene target, obtained with 60 fs laser pulses at 1019 W/cm2, with a very high temporal contrast (1010). The plasma frequency of this target corresponds to harmonics 15-16, thus excluding the CWE mechanism for the generation of harmonics of higher orders. Images on the right : harmonic spectra from orders 13 et 18, for different distances z between the target and the best focus. At the highest intensity (z=0), harmonics emitted by the ROM mechanism are observed above the 15th order. These harmonics have a much smaller spectral width then those due to CWE (below the 15th order). These ROM harmonies vanish as soon as the intensity is slightly decreased (z=100 pm), while the CWE harmonic persists even at lower intensities (z=200 pm).

[1] P.Monot et al, Opt. Lett. 29 (2004), 893 [2] F. Quéré et al, Phys. Rev. Lett. 96 (2006), 125004 [3] F. Brunei, Phys. Rev. Lett. 59 (1987), 52 [4] R. Lichters et al, Phys. Plasmas 3 (1996), 3425 cjüD HU1100123

Laboratory approach to natural craters, can we? Tara Desai', Dimitri Batani1, Marco Bussoli1, Annamaria Villa2 and Biljana Gakovic3 1Dipartimento di Fisicu "G.Occhialini", Universitá degli studi Mikmo-Bicocca, Piazza delkt Scienza i, 20126-Milano, Italy 2Dipartimento di Biotecnologie e Bioscienze, Universitá di Milano Bicocca, Piazza della Scienza, 20126-Milano, Italy 3Vinca Institute of Nuclear Sciences, Department of Atomic Physics, 11001 Belgrade, Serbia

In the present work we report an experimental study on the crater development using Nd:YAG laser system of 40 ps at 1.06 and 0.532 pm laser wavelength with optical energy ~100 and 50 mJ respectively. A flat aluminum (20x10x2 mm) of density 2.7 g/cc was used as a target. Experiments were performed in a plasma chamber under vacuum exceeding 10~4 torr. We have measured the diameter and depth of the craters with different techniques. Crater diameter was measured using optical microscope and images were recorded using CCD camera. Optical Confocal Microscope and profilometry were used to measure crater diameter, depth and crater lips. Our preliminary results show that the initial diameter (

an important role in estimating the final diameter as <Í>F= |+E0 where E is the incident energy and /3 ~0.30 under our experimental conditions using 0.532 pm laser. A similar scaling for the meteor-craters yield /3=0.20-0.25 for simple craters according to meteor study. Although energy variation is several orders of magnitudes (with few joules laser energy in the lab to megatons of meteor energy), physics of crater formation in both cases draws close resemblance. Aim of our work is to understand the physics of laser produced laboratory craters to recognize some aspects of the natural carters. Recently, Petawatt lasers have been proposed to study meteorite impact physics (Rubenchik LLNL report, 1999)

24 KM diameter natural crater, Australia. Laboratory crater on aluminum target

Several megatons meteors approaching the earth with velocity ~20-100 Km/sec is a rare event, approximately, once in million years but accompanying effects persist in time. Remnants of the craters (including simple or complex craters) provide information with substantial margin error about the cralering processes on the terrestrial surfaces (including earth, moon, Jupiter etc.) and, mass and velocity during impact of the dead meteor. Several efforts are being made to scale such events in the laboratory to understand the natural craters. Some of the experimental study by varying laser parameters and target materials may respond to the natural inquest of understanding some aspects of natural craters. Details of the work with merit and demerit will be presented. HU1100124 CWeT)

Broadband attosecond XUV pulses isolated by CEP-stabilized polarization gating E. Mével1, I. J. Sola1, L. Elouga1, E. Constant', V. Strelkov2,L. Poletto3, P. Villoresi\ G. Sansone4, E. Benedetti4, J-P. Caumes4, S. Stagira4, C. Vozzi4, M. Nisoli4 lCELIA, Université Bordeaux I, Talence, France 2 General Physics Institute of Russian Academy of Sciences, Moscow, Russia 3INFM - D.E.I. - Université cli Padova, Padova, Italy 4INFM - Dipartimento di Fisica, Politecnico, Milano, Italy

Generation of attosecond pulse trains is now currently achieved by proper control of the process of high-order harmonic generation (HHG) in noble gases, as theoretically suggested in 1992 [1]. Emission of an isolated 250 attosecond pulse has been demonstrated as well by selecting cut-off harmonics generated by few-cycle driving pulses with stable carrier-envelope phase (CEP). Nevertheless, such a pulse is only generated at photon energies around 100 eV with a typical bandwidth of 10 eV leading to 0.25 fs pulses [2, 3]. Here, as a alternative method, we use the polarization gating technique [4] applied to few-cycle driving pulses [5] with stabilized CEP [6] (with a residual fluctuation of 0.1 rad rms). Indeed, the harmonic emission over a broad spectrum can be temporally confined in the polarization gate, i.e., around the time where the polarization is close to linear. Experimentally, a pulse with a time dependent ellipticity is generated using two birefringent plates [7] producing two pulses with opposite hellicity and separated by a delay ő. For a delay and a laser pulse duration of 5-6 fs, a gate width shorter than half an optical cycle is created hence suitable for isolating a single attosecond pulse. However, the emission time inside the gate is linked to the CE phase of the laser field. Depending on the CE phase, the emission of one or two attosecond pulses is allowed within the gate [8, 9]. This should be detectable in the frequency domain as a variation of the modulation of the harmonic spectra upon changing the CEP value. In this work we report on measured extreme ultraviolet (XUV) spectra that clearly evidence a transition in the temporal evolution of the generated XUV radiation upon changing the CEP of the driving pulses: In argon (Fig. 1), the periodic change with a n CEP period from a clearly modulated spectrum to a broad continuum is the signature that a single or two attosecond pulses can be generated depending on the pulse CEP. Simulations shows that the 15 eV continuum (25 - 40 eV) supports an isolated 260 as chirped pulse (160 as after chirp compensation) with a high temporal contrast (less than 1% of the total energy in a satellite pulse).

Fig. 1. Lett : XUV spectra measured in argon for 51 different CEPs varied over 3 Jt for a gate width of 0,8 fs. Right corresponding experimental (a) and calculated (b) XUV spectra generated in argon for two CEP differing by n/2. (e) XUV intensity temporal profiles. XUV spectra generated in neon using the same gate parameters as for the figure 1 show the same n periodicity upon CEP but with a much stronger sensitivity to the CEP. Here, a single broadband XUV burst is emitted in another spectral range (35 - 70 eV). The simulations are also in good agreement with the results obtained in Neon and show that chirped isolated pulses of 205 as (85 as after chirp compensation) can be produced over a broad range of CEP in these experimental conditions. By setting slightly larger gate, the generation efficiency increases and the CEP evolution of the XUV spectrum becomes very similar to that displayed in figure 1 for Argon. More importantly, the cut off can then be extended beyond 100 eV hence the bandwidth of a single attosecond pulses can be further increased as shown in figure 2.

Fig. 2. XUV spectra measured in neon for 2 different CEPs differing by nt2 for a gate width of 0,8 fs.

It is essential to point out that the CEP stabilization is crucial to confine the generation process to a single XUV burst in a stable way. Indeed, when the XUV spectra are generated in neon for a gate width of about 1 fs, harmonics are resolved for every CEP indicating that more than one XUV pulse is emitted. Nevertheless, CEP dependent harmonic shift can lead to an apparent continuous spectrum when the CEP is not fixed. This is only when the CEP is stabilized that the observation of a continuous spectrum is an unambiguous signature of an isolated attosecond pulse.

In conclusion, we have achieved the confinement of the XUV generation to a single emission process using the technique of polarization gating with phase-stabilized few-optical-cycle driving pulses [10]. The signature of a single attosecond pulse emission has been observed in two gases, argon and neon, for three different spectral ranges, 25-40 eV in argon and 35-70 eV or 50-100 eV in neon. Sub-100 as pulses seems now achievable. The bandwidth of isolated pulses can be potentially extended to a several 100 eV and a duration of few attosecond could then be obtained after chirp compensation. Isolated attosecond pulses are becoming accessible in new spectral and temporal ranges and will benefit to new attosecond science from time resolved tomographic imaging of electron wave packet motion [11, 12] to electron-electron interaction dynamics at the atomic unit time scale.

References

1. G. Farkas and C. Toth, "Proposal for attosecond light pulse generation using laser induced multiple-harmonic conversion processes in rare gases," Phys. Lett. A Í68, 447-450 (1992). 2.1.P. Christov, M.M. Murnane, H. Kapteyn, "High-Harmonic Generation of Attosecond Pulses in the "Single-Cycle" Regime," Phys. Rev. Lett. 78, 1251-1254 (1997). 3. R. Kienberger, E. Goulielmakis, M. Uiberacker, A. Baltuska, V. Yakovlev, R Bammer, A. Scrinzi, Th. Westerwalbesloh, U. Kleineberg, U. Heinzmann, M. Drescher, and F. Krausz, "Atomic transient recorder," Nature 427, 817 (2004). 4. R B. Corkum, N. H. Burnett, and M. Y. Ivanov, "Subfemtosecond pulses," Opt. Lett. 19, 1870(1994). 5. Nisoli, M. et al., Generation of high energy 10 fs pulses by a new pulse compression technique. Appl. Phys. Lett. 68, 2793-2795 (1996).A. 6. Baltuska, Th. Udem, M. Uiberacker, M. Hentschel, E. Goulielmakis, Ch. Gohle, R. Holzwarth, V.S. Yakovlev, A. Scrinzi, T.W. Hansch, and F. Krausz, "Attosecond control of electronic processes by intense light fields," Nature 421, 611 (2003). 7. O. Tcherbakoff, E. Mevel, D. Descamps, J. Plumridge, and E. Constant, "Time-gated high- order harmonic generation," Phys. Rev. A 68, 043804 (2003). 8. V. Strelkov, A. Záir, O. Tcherbakoff, R. Lopez-Martens, E. Cormier, E. Mevel, and E. Constant, "Generation of attosecond pulses with ellipticity-modulated fundamental," Appl. Phys. B 78, 879 (2004). 9. Z. Chang Phys. Rev. A 70, "Single attosecond pulse and XUV supercontinuum in the high- order harmonic plateau," 043802 (2004). 10. I. Sola, E. Mével, L. Elouga, E. Constant, V. Strelkov, L. Poletto, P. Villoresi, E. Benedetti, J.-P. Caumes, S. Stagira, C. Vozzi, G. Sansone and M. Nisoli, « Controlling attosecond electron dynamics by phase-stabilized polarization gating », Nature Physics, 2, 319 (2006) 11. J. Itatani, J. Levesque, D. Zeidler, H. Niikura, H. Pépin, J. C. Kieffer, P. B. Corkum and D. M. Villeneuve, "Tomographic imaging of molecular orbitals", Nature 432, 867 (2004) 12. Nikura, H., Villeneuve, D. M., and Corkum, P. B., Mapping attosecond electron wave packet motion. Phys. Rev. Lett. 94, 083003-1-4 (2005)

Corresponding author E. Mével, e-mail: [email protected] CWe2^>

On the characterization of attosecond pulses P. Tzallas1, E. P. Benis1, M. Kovacev1, L. A. A. Nikolopoulos2, E. Papalazarou1, C. Kalpouzos1, G. D. Tsakiris3, and D. Charalambidis1'4 ' Foundation for Research and Technology-Hellas, Institute of Electronic Structure & Laser, PO Box 1527, GR-711 10 Heraklion (Crete), Greece. 2Department of Telecommunication Sciences and Technology, University of Peloponnisos, GR22100 Tripoli, Greece. 2Max-Planck-Institute fiir Quantenoptik, D-85748 Garching, Germany. 4 University of Crete, Heraklion (Crete), Greece.

We discuss metrology approaches targeting the rigorous temporal characterization of XUV attosecond pulse trains. These include 2nd order autocorrelation (AC), as well as IR-XUV cross correlation based techniques. A detailed analysis of our 2nd order AC measurement is presented [1], The analysis includes ion yield considerations, the spectral and temporal response of He two-XUV-photon ionization detector used, as well as spatiotemporal driving intensity effects on the measured attosecond pulse duration [2]. Towards the determination of the complete temporal distribution of the attosecond pulses, utilizing a frequency resolved two-XUV-photon ionization based 2nd order AC, the feasibility of recording two-XUV-photon induced energy resolved photoelectron spectra has been demonstrated [3], The spectra are produced through non-resonant two photon ionization of He by a superposition of the 9th to the 15th harmonics. Limitations of this approach originat- ing from the energy resolution requirements and the available electron yield will be discussed. Recently, an alternative 1R-VUV cross-correlation approach based on what is known as phase sensitive coherent control has been proposed [4] in order for the cross-correlation method to account for both the chirp between harmonics and chirp within the bandwidth of each harmonic. The applicability of the method has been demonstrated by the retrieval of the full spectral phase/amplitude distribution of the third harmonic (TH) of a 50fs Ti:Sapph laser pulse [5], From the retrieved distributions for an unstreched and a chirped TH pulse, their pulse duration has been found in agreement with the value estimated from lowest order perturbation theory.

1. P. Tzallas et. al, Nature, (London), 426, 267, (2003) 2. L. A. A. Nikolopoulos et. al, Phys. Rev. Lett., 94, 113905, (2005) 3. E. P. Benis et. al, New J. Phys., (in press) 4. E. Hertz et. at, Phys. Rev. A, 64, 051801, (2001) 5. E. Papalazarou, et. al, Phys. Rev. Lett., 96, 163901, (2006)

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Time-resolved luminescence spectroscopy of dielectric crystals under the condition of high excitation density M. De Grazia1, S. Guizard2, H. Merdji1, A. Belsky3, N. Federov3, M. Kirm4, E. Feldbach4, V. Nagirnyi4, S. Vielhauer4, and B. Carré1 'Service des photons, A tomes et Molécules, CEA-Saclay, France 2Laboratoire des Solidcs Irradiés, Ecole Polytechnique, CNRS, CEA, France 3CELIA, CEA-CNRS, Université de Bordeaux I, 33405 Talence, Bordeaux, France 4Institute of Physics, University of Tartu, 142 Riia Str., 51014 Tartu, Estonia

Dielectric crystals serve to a wide range of applications as radiation converters of the extreme UV (XUV) and X-rays in different areas of technology: medical scintillators for radiography, fast scintillators for high-energy physics, X-ray imaging, XUV beams monitoring, etc. The knowledge about the luminescence properties and the relaxation of electronic excitations in crystals exposed to the XUV radiation is crucial for these applications. So far the majority of the studies has been carried out using the low-intensity synchrotron radiation in the linear regime of excitation. The regime of intense irradiation, provided either by light (high-power lasers, X- and y-rays, etc.) or by particles (a-particles) causes different relaxation and luminescence processes in the crystals, which so far are generally not well understood. The recent development of intense XUV sources of ultra-short duration opens new perspectives for the studies of luminescence in solids [1, 2], In particular, the XUV femtosecond pulsed light source is an ideal tool for studying the effects of high excitation density on the relaxation processes. Short-wavelength radiation excites the electrons from the valence band and inner shells to the conduction band; the ultra-short pulse duration then facilitates the study of the charge carrier recombination dynamics in real time. The present study is aimed at understanding the non-radiative and radiative relaxation processes responsible for luminescence quenching mechanisms, energy transport to luminescence centres and interaction of elementary excitations such as excitons, electron-hole pairs. We report the experimental studies of the luminescence in dielectric crystals, using high-order laser harmonics (HOH) generated in rare gas as an intense ultra-short XUV source. The experiment took place at SLIC laser facility of CEA-Saclay, France, on the PLFA laser (Ti:Sapphire laser at 800 nm, 13 mJ, 1 kHz). The HOH beam is separated from the 1R beam

(Si02 plates), spectrally selected in the 60-40 nm range (metallic filters), and focussed onto the sample to a ~ 10,Hm focal spot size (off-axis parabola). We vary the XUV excitation density either by moving the sample out of the focal plane or modulating the pulse energy.

Preliminary results for CdW04 and BaF2 crystals show significant changes in the luminescence spectra or decay kinetics, when varying the excitation density. We propose a model of effects observed based on the interaction of excitons. A second series of experiments in Saclay is in progress for investigating other samples: CaW04, PbW04, YAG:Ce. The free electron laser (FEL) facility FLASH of HASYLAB at DESY in Hamburg, Germany, offers another possibility of ultra-short, very intense radiation in the XUV range. During the recent run the FLASH operated at 25.6 nm and 13.8 nm, providing 30 fs pulses of 25 and 10 [ti energy, respectively. A number of pure and doped crystals were investigated. The results obtained using the HOH and FEL sources will be compared.

References: [1] M. Kirm, A. Andrejczuk, J. Krzywinski, R. Sobierajski, Phys. Stat. Sol. (c) 2 (2005) 649. [2] P. Martin, A.N. Belsky, E. Constant, E. Mével, and F. Salin, IEEE Trans. Nucl. Sci. 48 (2001) 1137. CWe4^> HU1100127

Few-cycle isolated attosecond pulses G. Sansone1, E. Benedetti1, F. Calegari1, L. Poletto2,'P. Villoresi2, S. Stagira1, C. Vozzi1, S. De Silvestri1, M. Nisoli1 'CNR-JNFM - Dipartimento di Fisica, Politecnico, Piazza L. da Vinci 32, 20133 Milano, Italy 2CNR- INFM- D.E.I. - University di Padova, Padova, Italy

In the last few years the field of attosecond science has shown impressive and rapid progress, mainly due to the introduction of novel experimental methods for the characterization of extreme ultraviolet (XUV) pulses and attosecond electron wave packets. This development has been also triggered by significant improvements in the control of the electric field of the driving infrared pulses. Particularly interesting for the applications is the generation of isolated attosecond XUV pulses using few-cycle driving pulses [1]. In this case significant progresses have been achieved thanks to the stabilization of the carrier-envelope phase (CEP) of amplified light pulses [2], In this work we demonstrate that the polarization gating (PG) method [3,4] with few-cycle phase-stabilized driving pulses allpws one to generate few-cycle isolated attosecond pulses tunable on a very broad spectral region. The PG method is based on temporal modulation of the ellipticity of a light pulse, which confines the XUV emission in the temporal gate where the polarization is close to linear. The time-dependent polarization of phase-stabilized sub-6- fs pulses, generated by the hollow fiber technique, has been obtained using two birefringent plates. It is possible to create a linear polarization gate, whose position is imposed by the intensity profile of the pulse whilst the emission time is linked to the CEP of the electric field. The pulses have been focused onto a gas cell (Argon or Neon). The generated XUV radiation has been analyzed by using a flat-field spectrometer. Continuous XUV spectra, corresponding to the production of isolated attosecond pulses, have been generated for particular CEP values [5], Upon changing the rotation of the first plate it was possible to tune the XUV emission in a broad spectral range. We have then achieved a complete temporal characterization of the generated isolated attosecond pulses using frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG CRAB) [6]. The measured parabolic phase indicates the presence of a predominant second order dispersion (positive chirp), which is intrinsic to the XUV generation process. As recently demonstrated in the case of trains of attosecond pulses [7], the positive chirp of the radiation produced by high-order harmonic generation can be compensated for by the negative group delay dispersion of thin aluminum foils. Upon increasing the thickness of an aluminum plate we have obtained XUV pulses with duration shorter than 300 as (at 37 eV), thus corresponding to few cycles of the electric field.

References 1. R. Kienberger, E. Goulielmakis, M. Uiberacker, A. Baltuska, V. Yakovlev, F. Bammer, A. Scrinzi, Th. Westerwalbesloh, U. Kleineberg, U. Heinzmann, M. Drescher, and F. Krausz, Nature 427, 817 (2004). 2. A. Baltuska et al., Nature 421, 611 (2003). 3. P. B. Corkum, N. H. Burnett, and M. Y. Ivanov, Opt. Lett. 19, 1870 (1994). 4. O. Tcherbakoff, E. Mevel, D. Descamps, J. Plumridge, and E. Constant, Phys. Rev. A 68, 043804 (2003). 5. I. J. Sola et al., Nature Physics 2, 319 (2006). 6. Y. Mairesse and F. Quéré, Phys. Rev. A 71, 011401(R) (2005). 7. López-Martens et al., Phys. Rev. Lett. 94, 033001 (2005).

Corresponding author: Mauro Nisoli, e-mail: [email protected]; phone: +39 0223996167 HU1100128 CWe5>

Carrier-Envelope Phase Control of Electron Dynamics in Atomic and Molecular Systems Matthias Kling FOM Instituut voor Atoom en Molecuul Fysiea (AMOLF), Amsterdam, The Netherlands

The availability of laser pulses with a duration down to about hundred attoseconds (=10~16 seconds) has raised the prospect of studying the motion of electrons on the timescales where this motion occurs in nature and to study how electron motion drives structural dynamics in molecular systems. The type and amount of information that can be extracted from the electrons or ions that leave an atom, molecule or cluster upon irradiation with intense laser light is crucial for an understanding of the processes that led to their release and determined their final properties. Velocity-map imaging (VM1) has shown great promise for sub-femtosecond studies on complex systems, as the full 3D-momentum distribution can be extracted that contains not only spectral but also angular information. In a recent study using VM1 it was shown that a suitable interference of attosecond electron wave packets generated in the continuum by ionization may yield information on the wavefunction of the system.1 Laser light with a controlled evolution of the electric field E(t) = a(t)"cos(a»/ +

References [1] Remetter, T., et al., Nature Physics 2006, 2, 323. [2] Baltuska, A., et al., Nature 2003, 421, 611. [3] Kienberger, R., et al., Nature 2004, 427, 817. [4] Macklin, J. J., et al., Phys. Rev. Lett. 1993, 70, 766; L'Huillier, A., Balcou, P., Phys. Rev. Lett. 1993, 70, 774. [5] Lindner, F., et al., Phys. Rev. Lett. 2005, 95, 040401; Paulus, G. G, et al., Phys. Rev. Lett. 2003,91,253004. [6] Goulielmakis, E., et al., Science 2004, 305, 1267. [7] Rabitz, H., Science 2003, 299, 525. [8] Kling, M., et al., Science 2006, 312, 246. HU1100129

Above-threshold ionization of excited H-states by an ultrashort laser pulse: energy spectra of photoelectrons Alexey Kornev, Boris Zon Voronezh State University, Voronezh, Russia

An adiabatic solution to the time-dependent Schrödinger equation that describes the infinite motion of an electron in a Coulomb potential in the presence of a strong linearly polarized laser field, was obtained in Ref. [I]. It was shown that adiabatic approximation has had a good accuracy on condition that (in the atomic units) F/co »VE. Here F is amplitude of the laser field strength, cu is the laser frequency, E is typical value of the electron energy. Above-threshold ionization (ATI) of an H-atom by a light pulse was considered as the result of a bound-free quantum transition. The initial states were chosen unperturbed. The final states were modeled by adiabatic wave functions. The laser parameters, quantum numbers of the initial states and the energy of emitted electron are the input parameters of calculation algorithm. The energy- differentiated and angle-integrated probability of ionization are the output quantity. We have considered ATI of excited (2s, 2p, 3s, 3p, 3d) H-states by the pulse with the peak intensity of 3.45x1014 W/cm2 (barrier-suppression regime), the central wavelength of 800 nm and the FWHM of 2.5 fs for two cases which differ in the initial phase of the pulse ( 0=0 is the cosine form; Q=n!2 is the sine form).

We have compared our results with those obtained in analytical models (see Ref. [2-4]) for the case of monochromatic light field. To adapt them to the pulse and compare with our results, we have developed an appropriate kinetic model. 1 2 Results are presented below. Here £/p =E / (4&> ) is the ponderomotive energy.

[1] B.A. Zon and A.S. Kornev, JETP 96, 870 (2003); 101, 1009 (2005). [2] G.F. Gribakin and M.Yu. Kuchiev, Phys. Rev. A 55, 3670 (1997). [3] V.P. Kra.nov, J. Opt. Soc, Am. B 14, 425 (1997). [4] S.P. Goreslavskii, S.V. Popruzhenko, N.I. Shvetsov-Shilovski., and O.V. Shcherbachev, JETP 100, 22 (2005).

Alexey Kornev, e-mail: [email protected] Cwp

Electron correlation effects in two-photon double ionization of helium Philippe Antoine, Emmanuel Foumouo and Bernard Piraux Laboratoire de Physique Atomique, Moléculaire el Optique (unite PAMO) Université catholique de Louvain, 2 chemin du cyclotron, B1348 Louvain-la-Neuve, Belgium

We present an ab initio computational treatment of multiphoton single ionization (with or without excitation) as well as double ionization of two-electron atoms exposed to short wavelength electric fields. This treatment is time-dependent and based 011 a spectral method of configuration interaction type combined with Jacobi-matrix [1] calculations. It involves a complete treatment of electron-electron correlations in the initial state, during the time propagation and, more important, in the final state. This approach reproduces accurately the results obtained by state-of-the-art methods in the case of one-photon single and double ionization of He and H". In this contribution, we concentrate on the two-photon double ionization of helium. Such process may be either direct or sequential depending on the photon energy. For photon energies below 2 a.u. (that is the minimum energy required to ionize He+(ls)), the process is essentially direct. Our results for the double ionization cross section differ significantly from those obtained by neglecting electron correlation in the final state. The origin of this effect will be discussed in detail. Moreover our results suggest that the frequency dependence of the double ionization cross section is a signature of the electron-electron correlations in the final state. Finally, these results shed some light on the outcome of a recent and unique experiment performed by Hasegawa et al [2], The main issue in that case, is to analyze the relative importance, within the experimental conditions, of the various channels that lead to the electron double ejection in order to decide whether or not it is the direct process that has actually been observed. For photon energies above 2.a.u., the process is sequential and dominated by transition channels that require no interaction between the electrons.

[1] E. J. Heller and H. A. Yamani, Phys. Rev. A 9, 1201 (1974). [2] H. Hasegawa, E. Takahashi, Y. Nabekawa, K.. L. Ishikawa, K.. Midorikawa, Phys. Rev. A 71, 023407 (2005).

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Double ionization in Helium Ab initio calculations beyond the one dimensional approximation Camilo Ruiz, Luis Plaja, Luis Roso and Andreas Becker. Max Planck-Institut für Physik komplexet" Systeme Nöthnitzer Strafie 38 01187 Dresden, Germany

We present ab-initio computations of the ionization of two-electron atoms by short pulses of coherent radiation beyond the one-dimensional approximation. In the model the electron correlation is included in its full dimensionality, while the center-of-mass motion is restricted along the polarization axis. We show some result for Non Sequential Double Ionization (NSDI) as well as for SDI for high intensity low IR frequency. Some recent applications for this correlated system is also presented.

Camilo Ruiz Mendez [email protected]

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Determining the Electronic Structure of Molecules Using High Harmonic Emission David Villeneuve National Research Council of Canada, Ottawa, Canada

High harmonic emission is known to depend on the spatial shape of the electronic orbital that has been ionized. By rotating the molecule and recording high harmonic spectra, it is possible to build up a two-dimensional map of the transition dipole matrix elements. In some cases this information can be inverted to give an image of the orbital. Like everything in physics, the interpretation of the measurement requires a model through which we view the results. A number of assumptions are built into present models of high harmonic generation. For example, we assume the single active electron approximation. I will discuss multi-electron effects within the Hartree-Fock picture, including transitions between orbitals as the electron recombines. We assume that the ionized electron can be described as a chirped plane wave when it returns. I will discuss situations in which the plane wave approximation breaks down, in particular for the case where a nodal plane in the ground state wave function exists. I will also discuss gauge dependence in the model. The next step is to study changes to the electronic configuration in molecular systems in pump-probe geometries. It should be possible to observe changes to electronic symmetry caused, for example, by curve crossings.

Other authors: Paul Corkum, Jerome Levesque, Jiro Itatani, Dirk Zeidler, Yann Mairesse, Nirit Dudovitch, Daniil Kartashov

David Villeneuve National Research Council of Canada 100 Sussex Drive, Ottawa ON K.4A 3E7, Canada [email protected]

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Molecular and Materials Dynamics Probed by Coherent Electrons from High Harmonic Generation Luis Miaja-avila, Guido Saathoff, Nick Wagner, Andrea Wüest, Martin Aeschlimann, Ivan Christov, Henry Kapteyn, and Margaret Murnane JILA, University of Colorado Boulder, CO 80309-0440, USA

In this presentation, we will discuss the observation of the laser-assisted photoelectric effect on surfaces for the first time. This represents a high-field laser-dressing of the original manifestation of the photo-effect i.e. photoemission form a surface. To date, such a laser-assisted photoelectric effect (LAPE) has only been observed in isolated atoms, where it is used to measure femtosecond and attosecond duration x-ray pulses, as well for the study of ultrafast dynamics in atoms. In our work, a clean Pt(l 11) single crystal was used as the solid surface, since it exhibits a large density of states at the Fermi edge, with a characteristic peak-like structure in the photoelectron spectrum. In the presence of an intense laser field, sidebands appear in the Pt(l 11) photoemission spectrum. The modification of the photoelectron-spectrum by LAPE can be distinguished from simple heating of the electrons by the pump beam by varying the laser polarization, by measuring the mean energy of the photo-ejected electrons and showing that it does not change, and by successfully fitting the photoelectron spectrum to theory. This effect promises to be useful to extend EUV pulse duration measurements to higher photon energies, as well as opening up femtosecond-to-attosecond time scale electron dynamics in solid and surface-adsorbate systems.

We will also discuss the observation of intramolecular vibration dynamics using electrons rescattered during the process of high-order harmonic generation. We excite coherent vibrations in SF6 using impulsive Raman scattering (ISRS) with a short laser pulse. A second, more-intense laser pulse generates high-order harmonics of the fundamental laser, at wavelengths of ~20-50 nm. The high-order harmonic yield is observed to oscillate, at frequencies corresponding to all the Raman-active modes of SFg, with an asymmetric breathing mode most visible. This is in contrast to conventional ISRS where only the symmetric breathing mode of the molecule is observed. Our results indicate that high harmonic generation is a more sensitive probe of vibrational dynamics and may yield more information simultaneously than conventional ultrafast spectroscopic techniques. Since the de Broglie wavelength of the recolliding electron is on the order of interatomic distances, i.e. ~ 1.5 A, small changes in the shape of the molecule lead to large changes in the high harmonic yield. This work therefore demonstrates a new spectroscopic technique for probing ultrafast internal dynamics in molecules, and in particular on the chemically- important ground staté potential surface that is difficult to probe using other techniques. High harmonic generation from excited molecules may also be sensitive to Raman-active as well as infrared-active vibrational modes.

References 1. L. Miaja et al., "Observation of the Laser-Assisted Photoelectric Effect on Pt(l 11)", to be published in Physical Review Letters (September 2006). 2. N. Wagner et al., "Monitoring Molecular Dynamics using Coherent Electrons from High- Harmonic Generation", Proceedings of the National Academy of Sciences 103, 13279 (2006). CWeTT>

Optimization of high harmonic generation by genetic algorithm Constance Valentin, Olga Boyko, Gilles Rey, Brigitte Mercier, Evaggelos Papalazarou, Laura, Antonucci, and Philippe Balcou ' Laboratoire d'Optique Appliquée, CNRS - Ecole Polytechnique - ENSTA, UMR 7639, Chemin de la Huniére, F91 761 Pataiseau Cedex, France

High Harmonic Generation (HHG) is very sensitive to pulse shape of the fundamental laser. We have first used an Acousto-Optic Programmable Dispersive Filter (AOPDF) in order to modify the spectral phase and second, a deformable mirror in order to modify the wavefront. We have optimized harmonic signal using a genetic algorithm coupled with both setups. We show the influence of macroscopic parameters for optimization process.

Genetic algorithms have been already used to modify pulse shapes of the fundamental laser in order to optimize high harmonic signals [1,2], in order to change the emission wavelength of one harmonic [3] or to modify the fundamental wavefront to optimize harmonic signals [4,5]. For the first time, we present a systematic study of the optimization of harmonic signals using the AOPDF.

Signal optimizations by a factor 2 to 10 have been measured depending of parameters of generation. For instance, one of the interesting result concerns the effect of macroscopic parameters as position of the entrance of the cell with respect to the focus of the 1R laser when we change the pulse shapes. For instance, the optimization is higher when the cell entrance is above the focus where the intensity gradients are higher. Although the spectral phase of the IR laser is important for the response of one atom, the optimization depends also of phase- matching and especially of the effect of intensity gradients.

Other systematic studies have been performed as well as measurements of temporal profiles and wavefronts of the 1R beam. These studies allow bringing out the behaviour of high harmonic generation with respect to the optimization process.

[1] R. Bartels et al., Nature 406, 164 (2000) [2] Randy A. Bartels et al., Phys. Rev. A 70, 043404 (2004) [3] David H. Reitze et al., Opt. Lett. 29, 86 (2004) [4] P. Villoresi et al., Opt. Lett. 29, 207 (2004) [5] D. Yoshitomi et al., Appl. Phys. B 78, 275 (2004)

Constance Valentin [email protected]

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Attosecond Time-Frequency analysis of high harmonic generation by few cycle laser pulses Ph. Balcou, V. Pascal, Ch. Coquelet, O. Boyko, C. Valentin Laboratoire d'Optique Appliquée, ENSTA —Ecole Polvtechnique—CNRS F-91 761 Palaiseau, France

We will present the results of a time —frequency study of the process of high harmonic generation by a single atom on an attosecond time scale, based on numerical solution of the Time-Dependent Schrödinger equation. In addition to providing an illuminating illustration of the Carrier Phase dependence of HHG by short pulses, this approach also unravels new features, such as the gradual loss of coherence of the high harmonic emission in the course of the pulse, in particular in the decreasing edge. The consequences of active shaping of the temporal profde of the laser pulse will also be presented, such as the effect of temporal super- resolution shaping.

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Imaging molecular structure and dynamics using laser driven recollisions J.P.Marangos, S.Baker, R.Torres, N.K.ajumba, C.Haworth, J.Robinson, J.W.G.Tisch, M.Lein, C.Chirila, C.Vozzi, F. Calegari, E. Benedetti, G. Sansone, S. Stagira, M. Nisoli, C.Altucci and R.Velotta Imperial College, Max-Planck Instlule for Nuclear Physics, Polilechnico di Miano, University of Naples

Laser driven electron recollision provides a unique tool for measuring the structure and dynamics of matter. We illustrate this with experiments that use HHG to measure molecular structure with sub-Angstrom spatial and sub-femtosecond temporal resolution. Our recent work has looked in particular at the signal from high order harmonic generation which contains rich information about the structure and intra-molecular dynamics of small molecules. This we will illustrate by two types of experiment; (a) measurements of HHG from aligned molecular samples to observe two-centre recombination interference and electronic structure dependence of the angle dependent yield, (b) reconstruction of intra-molecular proton dynamics from the spectral dependence of the HHG using the intrinsic chirp of recolliding electrons. We experimentally investigate the process of intramolecular quantum interference in high-order harmonic generation in impulsively aligned C02 molecules. The recombination interference effect is clearly seen through the order dependence of the harmonic yield in an aligned sample. This confirms that the effective de Broglie wavelength of the returning electron wave is not significantly altered by acceleration in the Coulomb field of the molecular ion. For the first time, to our knowledge, we demonstrate that such interference effects can be effectively controlled by changing the ellipticity of the driving laser field Here we also report the results of angular dependence measurements of high order harmonics (17lh - 27th) from impulsively aligned organic molecules: Acetylene, Ethylene, and Allene.

Since these molecules have a relatively low lP an appropriately short pulse is required to produce as many harmonic orders as posible. This was provided by the -10 fs beam line of the ASTRA laser at Rutherford Appleton Laboratory whilst a somewhat longer pulse, properly forwarded with respect to the driving pulse, induced the molecular alignment. We demonstrate a new technique using high order harmonic generation in molecules to probe nuclear dynamics and structural rearrangement on a sub-femtosecond timescale. The chirped nature of the electron wavepacket produced by laser ionization in a strong field gives rise to a similar chirp in the photons emitted upon electron-ion recombination. Use of this chirp in the emitted light allows information about nuclear dynamics to be gained with 100 attosecond temporal resolution, from excitation by an 8 fs pulse, in a single laser shot.

Measurements on H2 and D2 agree well with calculations of ultra-fast nuclear dynamics in + the H2 molecule, confirming the validity of the method. Guided by this result, we have measured harmonic spectra from CH4 and CD4 to demonstrate a few-femtosecond timescale for the onset of proton rearrangement in methane upon ionization 2.

1. C.Vozzi et al." "Controlling two-center interference in molecular high harmonic generation", Phys. Rev. Lett., 95, 153902 (2005). 2. S.Baker, et al.,"Probing proton dynamics in molecules on an attosecond timer scale", Science, 312 424 (2006). Measurement of the attosecond emission from aligned molecules W. Boutu, H. Merdji, R. Fitour, P. Monchicourt, R Bréger, B. Carré and P. Saliéres Service des Photons, A tomes et Molecules, CEA-Saclay, 91191 Gif-sur-Yvette, France

Recently, a number of papers have demonstrated the interest of high-order harmonic generation (HHG) from molecules aligned with respect to the laser polarization. Itatani et al. (Nature 432, 867 (2004)) have shown that a precise characterization of the harmonic emission allows performing a tomographic reconstruction of the molecular orbitals that radiate. Kanai et al. {Nature 435,470 (2005)) have evidenced quantum interferences in the recombination process of HHG that are directly related to the molecular structure. In all of these papers, only the HHG intensity was measured. The relative harmonic phase, though more difficult to measure, contains important information on the interference process, and is needed for an ab initio tomographic reconstruction. Finally, while the attosecond emission from atoms has been thoroughly studied, in particular by our group (Mairesse et al., Science 302, 1540 (2003)), it has not been investigated in molecules.

In a first experiment (Wabnitz et al., EPJD (2006)), we measured the amplitude and relative phase of harmonics radiated by un-aligned nitrogen molecules. Small but reproducible deviations from the phase of harmonics generated in argon (same ionization potential as nitrogen) were measured for low orders. In a recent experiment, we have measured, up to high order, the harmonic amplitude and relative phase for aligned molecules (N2 and C02). In order to align the molecules, we used the so- called nonadiabatic technique: a rotational wavepacket is created by a strong enough and short aligning pulse, so that a field-free alignment is obtained at the revival (a few ps after the aligning pulse). The measurement of phase locking between neighboring harmonics was performed through the photoionization of a target gas by the harmonic beam in presence of a sufficiently intense "dressing" laser beam (RABITT technique).

The harmonic phase measured when the C02 molecules are aligned parallel to the generating laser polarization (at the revival of the rotational wavepacket, 22 ps after the aligning laser pulse) are significantly different from the Krypton case (which has a similar ionization potential). Up to harmonic 21, their behavior is similar, but at harmonic 23 we observe a phase jump spread over 3 harmonic orders. The value of the total phase shift is around 2 radians, which is close to the phase jump of n that is predicted when destructive interference occurs in the recombination process. The position of the jump coincides with the dip in the harmonic spectrum measured at harmonic 23 by Kanai et al. (Nature 435, 470 (2005)). This behavior disappears when the C07 molecules are aligned at 90°, which is consistent with the two-center interference model.

The reconstructed temporal profile of the attosecond pulse trains emitted by aligned C02 molecules are strongly affected by this phase jump that leads to a splitting of the pulses. We also investigated the case of aligned nitrogen molecules. We observed a phase jump at harmonic 25, but this jump is independent of the angle of alignment. The origin of this inter-

ference would thus be different from that observed in C02.

Corresponding author: Saliéres Pascal, [email protected] HU1100138

A High Average Power Few-cycle OPCPA Drive Laser for Attosecond Pulse Production Y. Tang1, P. Bates1-2, E.L. Springate1, I.N. Ross1, G.H.C. New2, R.A. Smith2, J.W.G. Tisch2, J.P Marangos2 ICCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OXUOQX, UK 2Blackett Laboratory, Imperial College London, Prince Consort Rd, SW7 IB W, UK

We have developed an advanced laser system based on Optical Parametric Chirped Pulse Amplification (OPCPA) technology [ 1,2] to act as a drive laser for single attosecond pulse production in XUV. This laser is comprised of a novel stretcher-compressor system, carrier envelope phase stabilisation, a diode-pumped high average power pump laser, and two stage optical parametric amplifiers (OPAs). It was designed to ultimately deliver 5fs pulses of ~10mJ at I kHz. In OPCPA, the conventional chirped pulse amplifier (CPA) is replaced by a non-linear crystal which provides gain via optical parametric amplification (OPA). OPAs have extremely large gain bandwidths that can allow amplification of the full bandwidth of a 5 fs pulse [1, 3]. Minimal thermal deposition in the OPA medium allows high average power operation with high beam quality due to the absence of thermal lensing effect. This enables orders of magnitude higher pulse energies at high repetition rate than that are available from the conventional CPA few-cycle systems. High average power OPCPA amplification requires a high pulse energy high average power pump laser and efficient conversion of pump to signal. The pump laser developed in house consists of a commercial oscillator-regen unit as the seed laser, providing 1 mJ, 40 ps pulses at 1047 nm which will be amplified in a diode-pumped high average power Nd:YLF amplifier to -200 mJ at repetition rates of up to 1 kHz. The amplified pump pulse will then be frequency doubled and image relayed onto the OPA crystals. The oscillator of the pump laser is electronically synchronised to the Ti:Sapphire OPA seed oscillator, reducing the pump-signal timing jitter in the OPA stages to less than 1 ps rms. Testing has shown up to 130 mJ infrared pulses at 10 Hz with good beam quality from the amplifier, and >50% frequency doubling conversion efficiency. Further development is being undertaken to increase both the pulse energy and repetition rate. An OPCPA laser system for 5 fs pulses requires a stretcher-compressor system capable of compensating the spectral phase across a 400nm bandwidth. We have designed a multi-element stretcher-compressor system including a prism stretcher, grating stretcher, grating compressor and an acousto-optic programmable dispersive filter (DAZZLER) for ultra-broadband spectral phase control. We use transmission gratings for compactness and efficiency, and testing has shown double- pass transmission of over 50% in both stretcher and compressor. We have shown the system can stretch and recompress a 10 fs pulse to within 1 fs of its transform limit. The OPA stages consist of two LBO crystals used in non-collinear geometry and have been modelled using a 2-D code which includes beam walk-off and diffraction effects. The first 7 mm long crystal is double passed using a 2 ps duration seed pulse. The high intensity of this short pulse enables us to easily achieve saturation for full bandwidth amplification. Initial tests of the first stage OPA show gains of >104 over the full 200 nm bandwidth of our seed pulse. The 3.5 mm long second stage will be seeded with the first stage output, stretched to 20 ps duration. This 2:1 pump-seed temporal ratio will maximise the amplification efficiency, with predicted final signal energies in the region of 10 mJ after recompression. [1] I. N. Ross, P. Matousek, M. Towrie, A. J. Langley, and J. L. Collier, Opt. Commun. 144, 125 (1997). [2] A. Dubietis, G. Jonusaukas, and Piskarskas, Opt. Commun, 88, 437 (1992). [3] T. Kobayashi and A. Baituska, Meas. Sci. Techno). 13, 1671 (2002).

Corresponding author: Yunxin Tang ([email protected]) CŐiD HU1100139

Attosecond Pulse Trains Generated using Two Color Laser Fields J. Mauritsson1'2, P. Johnsson1, E. Gustafsson1, A. L'Huillier1, K. J. Schafer2 and M. B. Gaarde2 'Dept. of Physics, Lund University, P.O. Box 118, S-221 00 Lund, Sweden 2 Dept. of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 USA

We present the generation of attosecond pulse trains from a superposition of an infrared (IR) laser field and its second harmonic. Our attosecond pulses are synthesized by selecting a number of synchronized harmonics generated in argon. By adding the second harmonic to the driving field the inversion symmetry of generation process is broken and both odd and even harmonics are generated. Consecutive half cycles in the two color field differ beyond the simple sign change that occurs in a one color field and have very different shapes and amplitudes. This sub-cycle structure of the field, which governs the generation of the attosecond pulses, depends strongly on the relative phase and intensity of the two fields, thereby providing additional control over the generation process.

The generation of attosecond pulses is frequently described using the semi-classical three step model where an electron is: (1) ionized through tunneling ionization during one half cycle; (2) reaccelerated back towards the ion core by the next half cycle; where it (3) recombines with the ground-state releasing the access energy in a short burst of light. In the two color field the symmetry between the ionizing and reaccelerating field is broken, which leads to two possible scenarios: the electron can either be ionized during a strong half cycle and reaccelerated by a weaker field or vice versa. The periodicity is a full IR cycle in both cases and hence two trains of attosecond pulses are generated which are offset from each other. The generation efficiency, however, is very different for the two cases since it is determined mainly by the electric field strength at the time of tunneling and one of the trains will therefore dominate the other.

We investigate experimentally both the spectral and temporal structure of the generated attosecond pulse trains as a function of the relative phase between the two driving fields. We find that for a wide range of parameters trains of attosecond pulses with only one pulse per IR cycle are generated. The presence of one attosecond pulse per IR cycle may furthermore be taken as evidence that consecutive pulses in the train have the same carrier envelope phase. When the attosecond pulses interact with a gas of atoms, electron wave packets are created if the photon energy exceeds the ionization potential. The wave packets are temporally localized with properties that are directly inherited from the attosecond pulses. If the ionization takes place in the presence of a strong IR field an energy exchange between the electrons and the field occurs. The amount of energy exchanged depends on the timing with respect to the phase of the IR field when the electrons are injected into the continuum. Using trains with only one pulse per IR cycle, all the wave packets are injected with the same timing with respect to the IR field, thus enabling us to measure their dynamics in the dressed continuum. Using a velocity map imaging spectrometer we can measure a projection of the three dimensional electron distributions.

Corresponding author. Johan Mauritsson, [email protected] CfhT>

Attosecond Ionization Dynamics P. Johnsson1, J. Mauritsson1'2, T. Remetter', K. J. Schafer2 and A. L'Huillier1 1 Department of Physics, Lund University, P. O. Box 118, SE-221 00 Lund, Sweden 2Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001, USA

In the interaction between light and matter, the central energy and bandwidth of the radiation, in relation to the energy structure of the studied atoms or molecules, are important parameters. Extreme ultraviolet attosecond pulses, produced through high-order harmonic generation, have during the last years been increasingly used for such studies, particularly in combination with intense infrared (IR) fields, for time-resolved studies of strong field processes. Attosecond experiments have so far utilized pulses with high central energies, in excess of the ionization, potentials of the studied species. When these pulses interact with matter they induce single-photon ionization, creating electron wave packets with a significant initial energy.

In the present work, we have generated attosecond pulse trains in xenon, with individual pulse durations of 370 as. Their central energy is 23 eV, which is above the ionization potential of argon (15.8 eV) and neon (21.6 eV), but below that of helium (24.6 eV). We let these pulses interact with the target gas in the presence of a strong IR laser pulse, and measure the ion yield as a function of the phase of the IR field at the time of arrival of the pulse. For helium, where the central energy of the pulses is below the ionization threshold, we find a significant enhancement of the ion yield when the IR field is present: In addition, the ion yield exhibits a sub-cycle modulation as a function of the IR phase. The origin of these effects can be understood through the measured photoelectron momentum distributions, and is confirmed by theoretical calculations based on the integration of the time-dependent Schrödinger equation.

Corresponding author: P. Johnsson, [email protected]

HU1100140 HU1100141

Direct interferometric measurement of the atomic dipole phase in high-order harmonic generation Chiara Corsi', Angela Pirri1. Emiliano Sali1, Alessandra Tortora1-2, and Marco Bellini1 >2 'LENS and Physics Dept., University of Florence, Sesto Fiorentino, Florence, Italy Ustituto Nazionale di Ottica Applicata - CNR, Florence, Italy

For low gas densities and negligible ionization, the so-called atomic dipole phase, connected with the electronic dynamics involved in the generation process, is the main source of phase modulation and incoherence of high-order harmonics. To accurately determine these laser- intensity-induced phase shifts is therefore of great importance, both for the possible spectroscopic applications of harmonics and for the controlled generation of attosecond pulses. In a semiclassical description, only two electronic trajectories contribute to generate plateau harmonics during each pump optical half-cycle. Electrons appearing in the continuum by tunnel ionization may follow two different quantum paths, namely a long (I) and a short (s) trajectory before recombination. According to the SFA approximation, the harmonic of q11' order acquires a phase proportional to the electronic classical action, and simply given by:

i (p q(r,t) = -a'ill(r,t) with j = /, .y

where a 'q are non-linear phase coefficients, roughly proportional to the time that the origi- nating electron spends in the continuum before recombination. The space and time variation of the laser intensity l(r,t), causes just a little phase modulation for the .?-trajectory harmonic component, while the /-trajectory component becomes strongly chirped and spatially defo- cused; this gives rise to two spatially-separated regions having different temporal coherence. Here we report the first direct measurement of such atomic dipole phase in the process of high-order harmonic generation. Differently from previous measurements based on the analysis of the frequency chirp of harmonic pulses, here phase shifts are measured in the most natural way, i.e., by interferometry. Two phase-locked pump pulses generate two phase- locked harmonic pulses in two nearby positions in a gas jet; one of them is used as a fixed phase reference while the generating intensity of the other is varied. The shift of the XUV interference fringes observed in the far field then gives a direct estimate of the intensity- dependent dipole phase. Besides being a conceptually much simpler kind of measurement, our approach has the important advantage of being able to clearly discriminate between the contributions of the two different quantum paths leading to harmonic emission.

Corresponding author: Marco Bellini Istituto Nazionale di Ottica Applicata - CNR Largo E. Fermi, 6 50125 Florence, Italy [email protected] djvD HU1100142

Realization of a time-compensated monochromator exploiting conical diffraction for few-femtosecond XUV pulses L. Poletto and P. Villoresi CNR - 1NFM Laboratory for UV and X-Ray Optical Research and Department of Information Engineering, University ofPadova (Italy)

The use of the XUV/X-ray radiation emitted in the interaction of femtosecond laser beam with the matter calls for optical instrumentation with unique characteristics. The peculiarities of this class of source are very challenging: in the case of harmonics generation the emission is discrete although tunable in the EUV, XUV and soft X-ray spectral region, highly collimated, of extremely short duration, presently in the attosecond regime, and the source is of very small spatial dimensions. A time compensated monochromator for the selection and utilisation of the harmonics is here presented. Its design prevents the negative effect of time broadening induced by selecting a single harmonic order with a conventional dispersing type of instrument. Time-delay compensated monochromators requires the use of at least two gratings in subtractive and compensated dispersion, in order to impose the two requirements: l) for all the rays transmitted by the instrument and having the same wavelength, the differences in the optical-path lengths that are caused by the first grating have to be compensated by the second grating; 2) two rays with different wavelengths within the spectrum of the pulse to be selected have to follow a path with the same optical length and have to be focused on the same point. Both these conditions are satisfied by a scheme with two equal concave gratings mounted with opposite diffraction orders [l]. A new configuration for a time-delay compensated monochromator based on the conical diffraction [2] has been recently theoretically analyzed [3], It envisage the use of two blazed gratings in the conical diffraction mounting, in which the light approaches the grating in a plane parallel to the direction of the grooves. It consists of a generation chamber, where the ultra-short Ti:Sapphire laser interacts with the gas jet generating the HHs, and of a monochromator divided in two eqital sections, each of them with fwo toroidal mirrors and a plane blazed grating. The first mirror of each section acts as a collimator, the second one acts as a condenser. The first section creates a spectrally dispersed image of the source on an intermediate plane, where a slit carries out the spectral selection of the HHs. Only a selected portion of the spectrum, i.e. a single harmonic or a set of few harmonics, is propagating through the slit toward the second section that compensates for the temporal delay introduced by the first grating and gives an image of the source on the output plane. The wavelength scanning is performed by rotating the gratings around an axis lying at the centre of the grating surface and parallel to the grooves. The optical setup and the XUV experimental characterization of the instrument will be detailed in the paper.

[1] P. Villoresi, "Compensation of optical path lengths in extreme-ultraviolet and soft-x-ray monochromators for ultrafast pulses", Appl. Opt. 38, 6040-6049 (1999) [2] W. Cash and R. Kohnert, "Very high X-ray efficiency from a blazed grating", Appf. Opt. 21, 17-18 (1982) [3] L. Poletto, "Time-compensated grazing-incidence monochromator for extreme-ultraviolet and soft X-ray high-order harmonics", Appl. Phys. B 78, 1013-1016 (2004)

Prof. Paolo Villoresi, Department of Information Engineering, University of Padova (Italy), via Gradenigo 6, 35131 Padova, Italy - paolo.villoresi@ unipd.it, tel: +39 049 827 7644; fax: +39 049 827 7699 Cm)

Short-pulse optical parametric chirped-pulse amplification for the generation of high-power few-cycle pulses Zsuzsanna Major1, József A. Fülöp1-2, Jens Osterhoff1, Rainer Horlein', Ferenc Krausz1-2, and Stefan Karsch1 'Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. I, D-85748 Garching, Germany 2Department für Physik, Ludwig-Maximilians-Universitát München, Am Coulombwall I, D-85748 Garching, Germany

In the quest for a way to generate ultrashort, high-power, few-cycle laser pulses the discovery of optical parametric amplification (OPA) has opened up the path towards a completely new regime, well beyond that of conventional laser amplification technology [ 1 ]. The main advantage of this parametric amplification process is that it allows for an extremely broad amplification bandwidth compared to any known laser amplifier medium. When combined with the chirped-pulse amplification (CPA) principle (i.e. OPCPA), on one hand pulses of just 10 fs duration and 8 mJ pulse energy have been demonstrated [2], On the other hand, pulse energies of up to 30 J were also achieved on a different OPCPA system [3]; the pulse duration in this case, however, was 100 fs. In order to combine ultrashort pulse durations (i.e. pulses in the few-cycle regime) with high pulse energies (i.e. in the Joule range) we propose to pump an OPCPA chain with TW- scale short pulses (100 fs—I ps instead of >100 ps of previous OPCPA systems) delivered by a conventional CPA system. This approach inherently improves the conditions for generating high-power ultrashort pulses using OPCPA in the following ways. Firstly, the short pump pulse duration reduces the necessary stretching factor for the seed pulse, thereby increasing stretching and compression fidelity. Secondly, also due to the shortened pump pulse duration, a much higher contrast is achieved. Finally, the significantly increased pump power makes the use of thinner OPCPA crystals possible, which implies an even broader amplification bandwidth, thereby allowing for even shorter pulses. We carried out theoretical investigations to show the feasibility of such a set-up. Alongside these studies we will also present preliminary experimental results of an OPCPA system pumped by the output of our Ti:Sapphire ATLAS laser, currently delivering 350 mJ in 43 fs. An insight into the planned scaling of this technique to petawatt levels (i.e. the Petawatt-Field-Synthesizer project at the MPQ) will also be given. References [1] A. Dubietis et al., Opt. Commun. 88, (1992) 437. [2] N. Ishii et al., Opt. Lett. 30, (2005) 567. [3] I.N. Ross et al., private communication

Corresponding author: Zsuzsanna Major, [email protected]

HU1100143 HU1100144

Effects of molecular orientation in the laser ionization of molecules Xinhua Xie ,Gerald Jordan, Christopher Ede and Armin Scrinzi Photonics Institute, Vienna U. of Technology, Gusshausstrasse 27/387, 1040 Vienna, Austria

Time-dependent electron momentum distributions are calculated during ionization of linear molecules by a strong laser pulse and upon recollision. For typical experimental laser parameters, we find a strong influence of molecular orientation and initial state symmetry on the total ionization rates and also on momentum distributions, compared to which the effect of electron correlation is less important for simple molecules. The dynamics of electron release and subsequent recollision with the parent ion largely deter- mines the time-frequency structure of harmonic radiation, which underlies the generation of attosecond XUV pulses and the time-resolved imaging techniques for the electronic structure of molecules. In the present work, the effects of orientation and initial orbital symmetry are investigated by solving the time-dependent Schrödinger equation for a two-dimensional diatomic molecule in the single-active electron approximation. As in the presence of strong external fields recolliding electrons cannot be easily separated from bound electrons, the electron wave packet is probed at some distance from where all electrons can be safely considered as detached. We find that momentum distributions strongly depend on molecular size, orientation of the molecular axis, and node structure of the initial state (Fig. 1).

Momentum (a.u.) Momentum (a.u.) Figure 1: Orientation dependence of the momentum distribution for a diatomic molecule without (left) and with (right) node in the ground state orbital

In order to determine the momentum spectra at the time of electron release and upon recollision, we classically propagate the Wigner distributions of probed wavepackets backward and forward in time, respectively. We find that the times of peak recollision current can vary strongly with the orientation of the molecule. Moreover, correlation effects on the electron spectra are included using the multi-configuration time-dependent Hartree-Fock method. The calculations are performed in three spatial dimensions with the restriction to cylindrical symmetry, where the molecule is aligned with the laser field. Correlation is studied by starting from ordinary single-configuration Hartree- Fock and systematically adding more configurations until convergence. We find modification of the spectra on the scale of only ~ 20 % for the aligned configuration.

*Xinhua Xie, e-mail: [email protected] Cjh7>

Generation of high energy self-phase-stabilized near-IR pulses by difference frequency generation and optical parametric amplification C. Vozzi, C. Manzoni, E. Benedetti, F. Calegari, G. Cirmi, G. Sansone, S. Stagira, O. Svelto, S. De Silvestri, M. Nisoli and G. Cerullo CNR-INFM- ULTRAS Dipartimento di Fisica, Politecnico, Piazza L. da Vinci 32, 20133 Milano, Italy

Control of the carrier-envelope phase (CEP) of light pulses is one of the most advanced frontiers of ultrafast optics. The generation of optical waveforms with reproducible electric field profile is important in the case of few-optical-cycle pulses for which a CEP variation produces a strong change in the waveform. CEP-dependent phenomena are observable in high-intensity interactions, such as above-threshold ionization [1] and high-order harmonic generation (HHG) [2,3], moreover CEP stabilization is a fundamental prerequisite for the production of isolated attosecond pulses through HHG [4], In this work we propose a novel scheme for the generation of high energy ultrabroadband near-IR pulses with passive CEP stabilization [5,6], starting from an amplified Ti:sapphire laser system. A phase stable seed is generated by difference frequency generation (DFG) between the frequency components of a hollow-fiber-broadened supercontinuum. This configuration intrinsically provides a high CEP stability due to the absence of mechanical delays between the frequency components undergoing the DFG process. The seed is then boosted in energy through a multistage near-IR optical parametric amplifier (OPA), exploiting the broad gain bandwidths available around degeneracy. We generated ~300-,mJ phase-stable pulses at 1.6 ptm and, after compensation of the negative dispersion by propagation through bulk media, we have obtained nearly transform-limited sub-25 fs pulse duration, which corresponds to less than 4 optical cycles at the considered carrier frequency. To verify that CEP-stabilization is preserved after the OPA stages and that amplified parametric superfluo- rescence is negligible, we used an f-to-2f interferometer. The appearance of a stable, high- contrast fringe pattern upon averaging is a clear proof of the shot-to-shot stability of the CEP due to the self-phase-stabilization mechanism. Once compressed, these pulses could be ideal.drivers for HHG experiments; indeed taking into account that the ponderomotive energy of the recolliding electron scales as the square of the laser carrier wavelength, the use of near-IR pulses will enable the generation of higher order harmonics. Even more interesting is the possibility of using this system as a front-end for high energy OPA pumped by a 100-mJ, 10 Hz Ti:sapphire laser system, enabling niulti- mJ-level self-phase-stabilized pulses.

References 1. G. G. Paulus et al., Nature 414, 182 (2001). HU1100145 2. A. Baltuska et al., Nature 421, 611 (2003). 3. M. Nisoli et al., Phys. Rev. Lett. 91, 213905 (2003). 4. R. Kienberger et al., Nature 427, 817 (2004). 5. A. Baltuska et al., Phys. Rev. Lett. 88, 133901 (2002). 6. C. Manzoni et al., Opt. Lett. 31, 963 (2006).

Corresponding author: Caterina Vozzi, e-mail: [email protected]; phone: +39 0223996085 HU1100146 Cfhip

Shaping of Picosecond Pulses for Pumping Optical Parametric Amplification József A. Fülöp1'2, Zsuzsanna Major1, Bálint Horváth1, and Ferenc Krausz1*2 1 Max-Planck-Jnstituí fiir QuantenopUk, Hans-Kopfermaim-Sti: 1, D-85748 Garching, Germany 2Department für Phvsik, Ludwig-Maximilianx-Universital München, Am CoulombwaU 1, D-85748 Garching, Germany

The use of temporally shaped pump pulses for optical parametric amplification (OPA) is expected to facilitate an increase of efficiency and suppression of possible spectral distortions in this process, since the gain sensitively depends on the pump intensity [1], Our simulations confirmed such beneficial effect of temporally shaped pump pulses on the OPA process. With the aim to realize an optimized OPA stage pumped by shaped pulses, a novel method for passively shaping narrowband picosecond pulses has been developed. The method is based on the pulse-stacking principle, where replicas of the incoming pulse are created in a specially designed four-beam interferometer (Fig. 1). The replicas are recombined with appropriate delays. The interferometer design allows for a unique flexibility in varying the pulse shape, since all relevant degrees of freedom, such as relative intensities and delays between the pulse replicas are independently adjustable. According to our calculations a pulse with a flat-top time profile would provide optimal conditions in the OPA process. Usually the pump pulse needs to be amplified in a conventional laser amplifier pior to the OPA. Our cross-correlation measurements showed that we are able to obtain shaped amplified pulses by shaping the amplifier input (Fig. 2). Furthermore, by precompensating the distortions introduced by the amplifier we demonstrated our capability to produce amplified pulses with a flat-top time profile.

References [1] G. Cerullo and S. De Silvestri, Rev. Sci. Instrum. 74 (2003) 1. Corresponding author: József A. Fiilöp, e-mail: [email protected] Cfh9>

Intense carrier-envelope phase stable few-cycle pulses at 2 /ím from a filament for high-order harmonic generation C.P. Hauri1, C. Blaga2, E. Power3, It. Schultz2, R. Lopez-Martens', L. DiMauro2 'Laboratoire d'Opüque AppHquée, École Polytechnique-ENSTA-CNRS, F-91761 Palaiseau Cedex, France, [email protected] 2Ohio State University, Columbus, Ohio, USA 3Center of Ultrafast Optical Science, Ann Arbor, Michigan, USA

We report on the generation of intense passively carrier-envelope phase stabilized 0.4 mJ pulses with less than 3 optical cycles at a wavelength of 2 fim. The initial 50-fs-long driving pulse from an optical parametric amplifier is artificially broadened by filamentary propagation in a rare gas resulting in a multi-octave spanning spectrum ranging from 2.5/ím to below 400 nm. A portion of this spectrum is compressed to 15 fs, which corresponds to less than 3 cycles of the electric field for a central wavelength of 2 //m. Such pulses are of particular interest for XUV photon and attosecond pulse production via high-order harmonic generation (HHG). In fact, a few-cycle source at 2 fim is in principle superior to comparable system based on Ti:sapphire amplification (A= 0.8 pm) for HHG since the highest reachable photon energy scales with A2. We measured the carrier-envelope phase of the few-cycle pulses to be preserved by the filament and show results on high-order harmonics using these pulses as driving field.

HU1100147 CfhuD HU1100148

Half cycle cut-offs in harmonic spectra and robust carrier-envelope phase retrieval J.W.G. Tisch*, J. S. Robinson ,C. A. Haworth, L. E. Chipperfield, P. L. Knight, J. P. Marangos Blacken Laboratory, Imperial College London, Prince Consort Road London, SW7 2BW, UK

In recent years the use of high order harmonic radiation to create and control events on attosecond timescales has grown at a phenomenal rate. With the use of carrier envelope phase stabilisation! and few-cycle laser systems2 it is possible to probe physical and chemical processes on unprecedented timescales. Here we report the first experimental observation of high harmonic emission at individual half-cycles of a laser pulse. We show that these half- cycle emissions are extremely sensitive to the CEP, providing a route to a new single-shot measurement technique of the CEP. We use this technique to measure the CEP of an 8.5 fs pulse at a centre wavelength of 800nm with an accuracy of 20 attoseconds, and show that the CEP of pulses as long as 13 fs (5 cycles) can be measured. With appropriate spatio-spectral filtering of the harmonic spectra our calculations show that we can isolate emission from an individual half-cycle cut-off which corresponds to a single isolated attosecond pulse of duration <300 attoseconds for an 8.5 fs laser pulse.

Relative CEP from phase stabilisation system (radians)

Figure 1. (a) Spectral line-out from HHG spectra recorded at four different CEP (ip) lock values, and for the CEP unlocked (red curves are raw data, grey curves are smoothed data). Three spectral bands are evident in each lineout that correspond to spectral cut-offs from individual half-cycles of the laser pulse. The positions of these halfcycle cut-offs is used to measure the CEP of the laser pulse, b) Graph shows the CEP retrieved with a fitting algorithm given the pulse from our FROG measurement, against relative CEP change from our phase stabilisation system.

References: 1. A. Baltuska et al. Nature 422189 (2003) 2.. M. Nisoli et al. Opt. Lett. 22 522 (1997)

* Corresponding Author: John W.G. Tisch, [email protected] Abstracts Posters HU1100149

About an Expansion of a High-Power-Laser Produced Plasma in Vacuum A. Aliverdiev1-5, D. Batani2, V. Malka3, T.Vinci2.4, M. Koenig4, A. Benuzzi-Mounaix4, R. Dezulian2 'Institute of Physics DSC RAS, Makhachkala, Russia 2Dipart. di Fisica "G. Occhialini", Universitá di Milano-Bicocca,Italy 3Lab. d'Optique Appliquee, UMR CNRS - ENSTA - Ecole Polytechnique, Palaiseau, France 4Lab. pour I'Utilisation des Lasers Intenses (LUL1), Ecole Polytechnique, Palaiseau, France 5International Humanitarian & Technical Academy, Makhachkala, Russia

We consider the results of an experimental investigation of the temporal evolution of plasmas produced by high power laser irradiation of various materials. The experiment was done at the LULI Laboratory (Ecole Polytechnique, Paris). The investigation of hydrodynamics expansion of laser- lenses produced plasmas (in the intensity range I = 1014 W/cm3) is fundamental for several physics areas, first of all inertial confinement fusion. Although several theoretical models of plasma expansion were developed already in the 70's and in the 80's and many, experiments have studied this aspect, still there are not many dean experimental results. In recent years, several techniques have been The sketch of the experimental set-up. introduced which allow the production of flat-top intensity profiles. Hence one fundamental experimental parameter, the laser intensity on target, is clearly defined, which is not the case with the usual Gaussian-like intensity distribution or, even worse, with typical focal spots affected by hot spots. This allows a well-characterized study of plasma expansion. Also, 2D effects in plasma expansion are strongly reduced, getting much closer to that described by 1D theoretical models. One of such technique is that of Phase Zone Plates which appeared in recent years, and which was also used in our experiment. The experimental set up includes a Nd:glass high power laser system with typical intensity of I014 W/cmJ (the temporal profile is approximately trapezoidal with rise and fall time of 150 ps and a flat top duration of 600 ps), a probe beam (Nd laser converted to 2co) coupled to an interferometer and to a streak-camera with ps resolution. The diagnostic system allows the evolution of the plasma density profile to be measured as a function of time. We report the result of 5 shots performed with 3 kinds of target material (Au, Al, and CFL). .The comparison between theoretical predictions, computer simulations and experimental data are provided. The authors warmly acknowledge the help of the LULI technical staff for the realization of this experiment. A.A. would like to thank the Ministry of Education and Science of Russia, SPIE, Cariplo Foundation-Landau Network-C'entro Volta, and ESF (COST Action P14).

A.Aliverdiev, e-mail: [email protected] HU1100150

Study of close to solid density plasmas generated by ultra-short laser pulses Mirela Cerchez, Jens Osterholz and Oswald Willi Institute of Laser and Plasma Physics, Heinrich-Heine-University Düsseldorf, Germany

The interaction of high contrast sub-10 fs laser pulses with solid targets has been studied using XUV spectroscopy and laser absorption measurements. Laser pulses with intensities up to 1016 W/cm2 have been used on different targets including carbon, boron nitride and lithium fluoride. The experimental results indicate that close to solid density plasmas with very steep density gradients are produced. Time integrated K. shell emission spectroscopy has been used to record the series limits for H-like and He-like resonance lines of carbon, boron and lithium. The limits are explained by pressure ionization, a "signature" of high density plasmas. From the emission spectra, the plasma density and electron temperature were inferred. A simple computer code [I] was used to model the expansion of the plasma and its time dependence for parameters similar to ones used in the experiment. The calculations predict a peak electron temperature for a lithium plasma of about 150 eV at a plasma density of 75% times solid. The rise time of the electron temperature is about 15 fs with plasma expansion of about 5%. Time dependent synthetic spectra have been calculated using the FLY code [2] to analyze the temporal evolution of the resonance emission lines starting from close to solid density. In order to understand the energy transfer mechanisms from the sub 10-fs laser pulse to solid matter, absorption measurements have been performed. The absorption fraction of the laser energy A was determined from the relation A = 1 - R, where R represents the fraction of the laser energy reflected by the solid target which was measured using an integrating Ulbricht's sphere. The dependence of the absorption fraction versus the incident angle for p- polarized laser beam was investigated. The experimental data were compared with various absorption mechanisms including resonance absorption [3], vacuum heating [4] and skin depth absorption [5], The model developed by Gibbon and Bell [6] for a steep but finite density gradient which describes the transition between resonance absorption and vacuum heating fits best the data. For our experimental conditions, a plasma density scale length L/A <0.1 is inferred.

[1] J. Osterholz et al., Phys. Rev Lett. 96, 085002 (2006) [2] R. W. Lee and J.T. Larsen, J. Quant. Spectrosc. Radiat. Transfer 56, 535 (1996) [3] W.L. Kruer, The Physics of Laser Plasma Interactions (Addison-Wesley Publishing Company, Inc., 1988) [4] F. Brunei, Phys. Rev Lett., 59, 52 (1987) [5] W. Rozmus and V. T. Tikhonchuk, Phys. Rev. A 42, 7401 (1990) [6] P. Gibbon and A. R. Bell, Phys. Rev Lett., 68, 1538 (1994)

Mirela Cerchez, [email protected] Laser based quasi-monochromatic electron acceleration L. Veisz1, K. Schmid1-2, S. Benavides1, U. Schramm2, S. Becker1-2, J. Fülöp2, Zs. Major1, J. Osterhoff1, S. Karsch1, D. Habs', F. Krausz1.2.3 Max-Planck-lnstitut für Quantenoptik, D-85748 Garching, Germany Lehrstuhl für Experimenlalphysik, Ludwig-Maximilians-Universitat, D-80799 München, Germany Institutfür Photonik, Technische Universitat Wien, A-J040, Wien, Austria

A breakthrough in laser based electron acceleration [1] has been achieved by obtaining intense (nC), quasi-monochromatic (10% bandwidth), short electron bunches with energies up to a few 100 MeV. The first results about electron acceleration are presented with the reconstructed ATLAS laser and the new laboratories in Garching. The laser delivers 7 TW (25) TW w/o (w) the final amplifier and has a pulse duration of <50 fs. The 7 TW version of the laser was focused onto a supersonic He gas jet with an F/3 off-axis parabolic mirror. The intensity on the gas jet was up to 1019 W/cm2. Various properties of the generated intense electron bunches were determined such as the number of electrons, angular properties and electron spectrum. The number of electrons was measured with an integrating current transformer and resulted in 400-600 pC charge, corresponding to 3- 4xl09 electrons. The transversal profile and the angle of divergence of the electron beam were obtained using a LANEX screen and a CCD. An angle of divergence of >=7 mrad was measured indicating a well collimated beam. A focusing permanent dipole magnet spectrometer (with 5cm gap and 0.9T magnetic field) was applied to determine the electron spectrum. This device has a good energy resolution (~1 %), has an on-line detection system and supports radiation protection by bending the electrons downwards. LANEX screens, scintillating fibers with CCD and imaging plate were used as alternative detections. The electrons had under specific circumstances quasi-monochromatic spectrum with energies up to 50 MeV. Further systematic study and optimization of the electron acceleration is planned by using the full power of ATLAS, focusing with large F-number optics and applying a novel 10 TW OPCPA system [2] with 10 fs pulse duration, which has the potential to generate stable electron beams.

[1] S. P. D. Mangles et al., Nature 431, p. 353 (2004); C. G. R. Geddes et al., in ibid, p. 538; J. Faure et al., in ibid, p. 541. [2] F. Tavella et al., Appl. Phys. B 3, p. 753 (2005)

Corresponding author: László Veisz, E-mail: [email protected]

HU1100151 New nonlinear quantum electrodynamical processes accelerating the free charged particle in interaction with intense laser radiation F.F. Körmendi * Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences P.O.BOX49, H- 1525 Budapest, Hungary

It has been proven in [ 1,2 ] that at well-defined above-threshold incident laser beam intensities

Ic an integral number of photons N can be absorbed by a truly free electron at simultaneous nonforward elastic scattering of n other photons, obeying four-momentum conservation. The applications of such multiphoton processes to the construction of laser accelerators and intense X-ray generators are analyzed in [ 3,4 ]. In this work the described nonlinear quantum electrodynamical phenomena are generalized to the absorption of N photons with simultaneous inelastic scattering of n other quanta by a free charged particle. Such processes appear at higher above-threshold intensities than the previous ones, giving, however, more effective particle acceleration gradients. While Ic is proportional to the oscillatory energy of the harmonically oscillating electron in the former case, the expression for the above-threshold intensity in the latter reflects the characteristics of the anhannonically oscillating charged particle. The appropriate differential cross sections and acceleration gradients are calculated with the help of diagram techniques given in [5],

References : [ 1 ] F. F. Körmendi, Opt. Acta 28, 1559 ( 1981 ) [ 2 ] F. F. Körmendi, Opt. Acta 31, 301 ( 1984 ) [ 3 ] F. F. Körmendi and Gy. Farkas, Phys. Rev.A 53, R637 ( 1996 ) [ 4 ] F. F. Körmendi and Gy. Farkas, Laser Phys. 7, 583 ( 1997 ) [ 5 ] F. F. Körmendi and Gy. Farkas, Phys. Rev.A, 59, 4172 ( 1999 )

* Visiting physicist. E-address : [email protected]

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The temperature evolution in a laser heated plasma N. Mimes and A. H. Belbachir Laboratory for Radiations Analyses and Applications (LAAR) Department of Physics, University of Sciences and Technology of Oran M. B. (USTO) P. O. Box: 1505, El-M'Nouar, Oran, Algeria Electronic mail: [email protected]

The thermal effect induced by a laser beam in a hot homogeneous and inhomogeneous plasma has been studied using the kinetic theory. Our mathematical model is based on a perturbative approch which let us to obtain tow nonlinear coulped equations for the electronic temperature and a density. The tow coupled equations which are the background of our study, are treated in tow considerations homogeneous and inhomogenous plasma. A general and exact expressions have been derived for the electron temperature depending on the space and the time. The analytical solutions show that the electron temperature evolution follows an evolution patern similar to that of the laser pulse, either in the homogenous or inhomogeneous plasma. In addition to a week gradient of the temperature in the z direction of the laser inhomogeneity (i.e. the laser direction incidence). Our results agree with its of the litterature (theoritical and experimental ones).

Key words : laser plasma interaction, Plasma temperature, electronic distribution function.

HU1100153 Surface modification of multilayered titanium-aluminium nitride coating with high intensity IR laser beam B. Gakovic1, M. Trtica1 P. Panjan2, M. Cekada2, M. Panjan2 'Institute of Nuclear Sciences "Vinca", P.O. Box 522, 11001 Belgrade, Serbia 2Jozef Stefan Institute, Jamova 39, lOOOLjubljana, Slovenia

Multilayered coatings have a number of advantages over single layers as they combine the attractive properties of several materials as well as exhibiting some completely new properties. Multilayered coatings such as titanium nitride/titanium-aluminium nitride (TiN/TiAIN) possess better mechanical properties than single layer coatings. Due to its high hardness and brittleness, mechanical micro structuring is extremely difficult, thus the laser beam treatment is one of possible solutions. Studying of interactions of laser beams with hard coatings has both application and fundamental importance. The research objective of this work was the study of surface modifications of TiN/TiAIN coating, induced by high intensity laser irradiation. The surface modification of multilayered coating was performed in air with focused TEA C02 laser beam. The laser operated at following conditions: TEM00 mode, pulse energy 70 mJ, temporal pulse duration 80 ns and peak power density of 10'° W/cm2. Multilayered hard coatings TiN/TiAIN was deposited on the polished hot work tool steel plates. The deposition system has four vertical unbalanced mag- netron sources in closed-field configuration with the ability to control their power. The total coating thickness was 2,17 ptm consisted of 45 layers, while 0.5 /um thick TiAIN was deposited as a top layer. The modulation period of multilayered structure was about 80 nm. Generally, surface modifications of coatings induced by laser radiation have shown their dependence on laser pulse energy density, peak power density, pulse duration, number of accumulated pulses, laser wavelength, as well as on material properties. The energy absorbed from the laser beam is converted into thermal energy, which generates effects such as melting, vaporization, dissociation or ionization of the vaporized material, exfoliation, and shock waves in the vapour and the solid. After action of successive laser pulses of 35 J/cm2 the modifications of the TiN/TiAIN multilayered coating were registered. As a function of accumulated laser pulses the experiments have shown the following effects: (i) surface modification on micro- and nanometer scale (ii) formation of craters with clear central part and narrow periphery (iii) plasma formation in front of target. The surface characterization of the samples prior and after laser irradiation was carried out by optical microscope, scanning electron microscope, atomic force microscope and profilometry. References 1. P. Panjan, B. Navinsek, M. Cekada, A. Zalar, Vacuum, Vol. 53 (1999) 127-131. 2. B. Gakovic M. Trtica, P. Panjan, M. Cekada , Applied Physics A-Vol. 79 (2004) 1353-1355. 3. M. Trtica, V. Tarasenko, B. Gakovic, A. Fedenev, Lj. Petkovska, B.Radak, E. Lipatov, M. Shulepov, Applied Surface Science, Vol. 252 (2005) 474-482.

Corresponding author: Biljana Gakovic (e-mail: [email protected])

HU1100154 Surface modifications of silicon using the high intensity Nd:YAG laser Milan Trtica1, Biljana Gakovic1, Dimitri Batani2, Tara Desai2, Irena Pongrác1 'Vinca Institute of Nuclear Sciences, P.O. BOX 522, 11001 Belgrade, SERBIA 2Universita degli Studi di Milano Bicocca, Dipartimento di Fisica "G. Occhialini", Piazza della Scienza 3, 20126 Milano, ITALY

Surface modification of semiconductor materials such as silicon by various types of energetic beams including the laser radiation is of a great fundamental and technological importance. The interest in studies of laser beam interaction with silicon is still extremely high. Silicon exhibits very good physico-chemical characteristics like high melting/boiling point, thermo- dynamic and chemical stability, semi-conducting properties, etc. and hence very attractive in electronics, semi-conductors industries, etc. In the present work surface morphological effects on a crystalline silicon target due to interaction of Nd:YAG laser radiation (TEM00 mode), pulse duration of 40 picosecond at 532 nm are reported. The sample was a crystalline silicon plate (dimensions of 10mm x 10mm x 0.5mm) with typical greyish colour. The surface roughness of the sample was about 0.1 pm. The samples were irradiated in air, at the atmospheric pressure. The p-polarized laser beam was incident normal to the target surface. Various analytical techniques were used for the characterization of the sample before and after laser irradiation using X-ray difractometry, microscopy (optical, SEM, AFM), etc. Our experimental results show that laser energy flux (LEF) exceeding to 0.7 J/cm2 (i.e. peak intensity - 2 x 1010 W/crn2) was sufficient for inducing surface morphological changes on the samples. The absorbed laser energy generates a series of effects such as melting, vaporization of the molten material, cracking, etc. The morphological modifications of the silicon surface can be summarized as follows: (i) Intense damage in the central zone of the irradiated area was recorded in the flux range 0.7 to 22.5 J/cm2 (with 100 accumulated laser pulses), (ii) Appearance of a wave-like microstructures (MS) across the entire irradiated spot for all the flux range (for low number of accumulated pulses). The estimated spatial wavelength of MS was about 10 microns, and (iii) creation of hydrodynamic features at the periphery, like resolidified forms, were expressed for higher laser flux. The creation of microstructures is very complex process. Preliminary consideration, among other, can include interaction of the incident wave with the surface electromagnetic waves. Further investigation and details of the work will be presented during the conference.

E-mail (for correspondence): [email protected]

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UJírafasí laser ablation of graphite Miklos Lenner, Andrey Kaplan, Christophe Huchon and Richard E. Palmer Ncmoscale Physics Research Lahoratoiy, School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK, Email: [email protected]. hham. ac. uk

The application of intensive laser pulses to surfaces can lead to ablation, i.e. material removal accompanied by emission of neutral and charged particles. Ablation has found widespread technological applications in the past decade. On the fundamental side, experiments shed light into the redistribution of excitation energy on time scales shorter than lattice vibrations and differentiate electronically-driven processes from thermal ones.

We have performed laser fluence dependence measurements with multiple shots, which allowed us to identify different ablation regimes. Up to fluences of order of =U/cm2 the ion yield increases nonliearly with increasing laser fluence, independently of the pulse duration. Observed momentum ratios of single, double and triple charged carbon atoms show clear evidence of impulsive CE. For higher laser fluences we observed saturation of the ion signal + + and clusters in the mass range between Cs and C/0 show the same kinetic energy (rather than momentum). We attribute this kinetic energy equilibration to plasma generation. In addition, the measurements indicate that ion emission threshold depends on the pulse duration.

We repeated the measurements applying single-shot laser pulses onto an HOPG target, whereas all other experimental conditions were unchanged. The spectra show substantial differences to the multishot ones. For fluences slightly above 90mJ/cm2, formation of medium- size carbon clusters (N<20) as well as nanotubes is observable. In contrast to the multishot- results, for F> 150 mJ/cm2 the high-mass end of the spectrum shifts to lower masses with increasing fluences. Above =250mJ/cm2 fullerenes and nanotubes completely disappear and only small clusters are generated (N<5).

Surface analysis with an atomic force microscope (AFM) clearly showed formation of oriented structures along crystallographic axes (width < 500nm, height 30-40nm, length a couple of microns). The structures consist of terrace-like hills, whose appearance supports the theory of cluster emission in form of graphene flakes, and is consistent with our earlier observations.

Further analysis of the time resolved ablation measurements lead us to create a so-called "fragmentation correlation map", which shows possible temporal correlations between different carbon clusters in their generation process. To prove the validity of the map, we studied the + kinetics of the fragmentation of fullerenes and C2 clusters. This approach may also open the way to determine the temperature of the emitted ions and thus to estimate the transient surface temperature.

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Simulation of primary processes for laser-induced plasma by short laser pulses in KDP crystal R. Gayet1, S. Jequier1, V. Rodriguez2'1, H. Bachau', G. Duchateau3',:. A. Dyan3, H. Mathis3 'CEL1A, Université Bordeaux I, 351 Cours de la Liberation, 33405 Talence Cedex, France 2Departamento de Fisica, FCEyN, Universidad de Buenos Aires, 1428 Buenos Aires, Argentina 3CEA, Centre d'Etudes du Ripaull, BP16, 37260 Monts, France

A theoretical approach designed for the description of local micro-plasma formation induced by short laser pulses in KH2P04 (KDP) crystal is addressed. Indeed, when such a crystal is illuminated by short pulses, the early stage of photo-production, enhanced by local defects [1, 2], leads to a subsequent strong electronic absorption revealing a transient metallic-like behavior. The lattice then is rapidly heated up by electron-phonon coupling at temperature as high as 10000K [3], This results in the local formation of a micro-plasma whose initial electronic energy distribution, which can be used in Particle-ln-Cell codes, may be predicted by the present approach.

The latter includes both, electron promotion from the valence band to the conduction band, and the subsequent interaction with phonons and photons. The electron promotion is described by a theoretical method based on Coulomb-Volkov (CV) wave functions whereas the electron diffusion in the conduction band is described by the standard Boltzmann's formalism. Although results about diffusion are shown, the present work focuses on the photo-production step. Hence, an extension of a previous theory [4], which has been developed essentially to describe ionization of atoms or molecules by intense femtosecond laser pulses, is under way. The first theory gives reliable predictions whenever both, (i) the photon energy is greater than the ionization potential, and (ii) perturbation conditions prevail. The restriction (i) prevents from intermediate state contribution to the ionization mechanism. The CV approach has been improved by introducing these states in the initial wave function, thus leading to an excellent agreement with predictions based on a full numerical solution to the time-dependent Schrödinger equation [5], Further, keeping the restriction (i), one can discard the condition (ii) by introducing a time-dependent initial state population in a CV approach [6],

Since defects induce intermediate states in the gap [2], they are good candidates to produce localized micro-plasmas. Thus, the improved CV approach [5] may be adapted to the condensed matter problem. It requires the knowledge of wave functions and energy levels induced by defects. It is achieved by ab-initio DFT (Density Functional Theory) calculations that provide wave functions developed on a plane wave-basis set. The feasibility of our approach is supported, firstly, by theoretical developments, and secondly, by preliminary calculations based on a simple atomic model in condensed phase conditions.

[1] C.W. Carr, H.B. Radousky and S.G. Demos, Phys. Rev. Lett. 91, 127402 (2003) [2] C.S. Liu et al, Phys. Rev. B 72, 134110 (2005) [3] C.W. Carr et al, Phys. Rev. Lett. 92, 087401 (2004) [4] G. Duchateau, E. Cormier and R. Gayet, Phys. Rev. A 66, 023412 (2002) [5] V.D. Rodriguez, E. Cormier and R. Gayet, Phys. Rev. A 69, 053402 (2004) [6] R. Gayet, J. Phys. B: At. Mol. Opt. Phys. 38, 3905-3916 (2005)

* Guillaume Duchateau, [email protected] CphD

Two-Photon Ionization of He Atoms through a Superposition of Higher Harmonics Imre Ferenc Barna Hungarian Academy of Sciences KFKI Atomic Energy Research Institute PO. Box 49, H-I525 Budapest, Hungary

We present a coupled-channel calculation of two-photon single-ionization of He by a superposition of the 7lh to the 13th harmonic of a Ti:sapphire laser. Solving the time-dependent two-electron Schrödinger equation for the He atom in a coherent polychromatic field the single-ionization probabilities are calculated. Besides Slater-like orbitals we use regular Coulomb wavepackets in our configuration interaction basis to describe the single- and double-electron continuum. A detailed description of our coupled-channel method can be found in our former studies [ 1,2]. Linearly polarized laser pulses are used in the length gauge within the dipole approximation. We apply cosinus squared normalized envelope functions . The pulse intensity is varied between 1010 and 1014 W/cm2, the total duration of each of the harmonics are in the range of 36 and 49 femtoseconds. Our results are compared with another ah initio calculation where spline basis sets are used[3].

A reasonable agreement is found and discussed.

References: [1] I.F. Barna, Ionization of helium in relativistic heavy-ion collisions, Doctoral Thesis, University of Giessen (2002) „Giessener Elektronische Bibliothek" http://geb.uni-giessen.de/geb/volltexte/2003/1036 [2] l.F. Barna, J. Wang and J. Burgdoerfer: Phys. Rev. A 73, 023402 (2006) [3] N.A. Papdogiannis, L.A.A. Nikolopoulos, D. Charalambidis, G.D. Tsakiris, P. Tzallas and K. Witte: Phys. Rev. Letter. 90, 133902 (2003)

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A relativistic generalization of the Kramers-Henneberger transformation Madalina Boca1, Viorica Florescu1 and Mihai Gavrila2 1University of Bucharest, Department of Physics, MGII Bucharest-Magurele RO-Ü77125 2FOM institute for Atomic and Molecular Physics, Amsterdam, 1098 SJ, The Netherlands

We propose a generalization of the Kramers-Henneberger transformation in the case of Dirac equation for an one-electron atom interacting with an arbitrary plane-wave laser pulse. This transformation leads to a Dirac Hamiltonian consisting of two terms: the first one is the free particle Dirac Hamiltonian and the second one contains the entire electromagnetic field dependence through a generalized translated potential.

The exact transformed equation is difficult to handle numerically, as the generalized translated potential is a non-local time-dependent matrix operator. However, if the studied atom is a light one, and the initial wavefunction contains only low momenta, approximations are justified. After some further manipulations one obtains a Schrodinger-like equation, with a Hamiltonian containing explicitly the first order retardation correction in the kinetic term and pure relativistic effects through a modified, time-dependent, atomic potential.

Using our equation we numerically calculate the survival probability of the Hydrogen atom acted upon by a high-intensity, high-frequency very short laser pulse and compare it with the results obtained with i) the non-relativistic dipole approximation and ii) the non-relativistic approximation with the first order retardation correction included. The comparison is done for several values of the laser pulse duration and intensity.

Coresponding author: Madalina Boca, e-mail [email protected]

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Theory of Landau—Dykhne and dipole-forbidden transitions Alexey Kornev, Boris Zon Voronezh State University, Voronezh, Russia

Adiabatic approximation of Landau-Dykhne (LD) [1] is used to describe bound-bound tun- nelling transitions of electrons in the framework of two-level model in the presence of monochromatic laser field Fsinw/, where F is the amplitude of the laser field strength, co is the frequency. However, if transitions between initial |/) and final |/) states are dipole- forbidden, the standard LD theory results in zero transition rate. To eliminate this disadvantage, the LD theory has been generalized on the case when bound states satisfy two-photonic selection rules. An expression for rate of transition between states which satisfy two-photonic selection rules, in the LD model has the form: ^;')~exp[-2;7/(y,K)/c(y,K)]. Here >7 = 1,2,... is the parameter of the resonant transition,

is a number similar to the Keldysh parameter; zlf is a two-photon matrix element of z- coordinate, a is the field-independent parameter; is a two-photon matrix element of Cartesian z- coordinate; a = ar-ai is the difference between polarisabilities of final and initial states. Two-parametric functions /(y,k) and ct(y,k) can be expressed in terms of elliptic integrals. Their approximate analytical forms are also obtained. It is possible to express the transition rate in the closed analytical form for two limiting cases. In the low-intensity limit, y~ » 1, and

V^lefl + sinS^"5' f2\ 4to/(. v cos 8 Here n » 1 to satisfy adiabaticity condition; 8 = arctan k . Thus, in the weak-field limit, excitation regime is n -photon. In the high-intensity limit, y2 1, and

„.(„, 0.874;; IVJf ~ exp< -p—cos8(l - sin 8)

Thus, in the strong-field limit, excitation regime is tunneling.

[1] N.B. Delone and V.P. Krainov, Atoms in Strong Light Fields. Springer Ser. Chem. Phys., New York, 1985, Chap. 4, Vol. 28. Alexey Kornev, e-mail: [email protected] CtkD

The Floquet quasienergy spectrum of rare gases Emine ME§E and R M Potvliege2 1 Department of Physics, Dicle University, Diyarhakir 21280 TR 2 Department of Physics, Durham University DH1 3LE, UK

The Floquet quasienergy spectrum of argon in a strong laser field is presented for several wavelengths between 248 nm (for intensities up to 1016 W cm-2) and 800 nm (for intensities up to 1014 W cm"2). The dependence of the spectrum on the laser wavelength is discussed. The calculation is done using expansions on a discrete complex basis, the atom being described by a one-electron model potential. The results at 248 nm are compared to those obtained by Plummer and Noble using the R-Matrix Floquet method [1], Those at 800 nm extend a recently compiled quasienergy map of this atom [2], The accuracy and the limitations of the calculations are discussed. The quasienergy spectrum of helium in a strong 800 nm field is also presented.

[1] Plummer M and Noble C J 2000 J. Phys. B: At. Mot. Opt. Phys. 33 L807. [2] Potvliege R M and S To he published

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Origin of the side peaks appearing in the above-threshold ionization spectra of Mg Gabriela Buica1,2 and Takashi Nakajima1 'Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan 2 Institute for Space Sciences, P.O. Box MG-23, Ro 77125, Bucharest-Magurele, Romania

Above-threshold ionization (ATI), a well studied process by now, is a process in which atoms absorb more than the minimum number of photons required to be ionized. The ATI spectrum consists of a series of peaks equally separated by the photon energy. We have theoretically investigated above-threshold ionization and ionization yield of Mg, a two-valence electron atom, in linearly and circularly polarized laser pulses. Since the first excited state of Mg is located only at a few eV from the ground state while those of rare gas atoms are at least several eV from the ground state, one can imagine that the low energy states may play important roles in the ATI spectra of Mg compared with rare gas atoms. The laser frequencies we have chosen correspond to the second and third harmonic of a Ti-sapphire laser. Numerical ab-initio data have been obtained by the solving the time-dependent Schrodinger equation on a discretized atomic basis. Interestingly we have found that the ATI peaks are accompanied by side peaks, which, after the detailed theoretical study to be presented in this paper, are attributed to the real excitation of some off-resonant low-lying bound state, such as 3skp (k=3,4,5,..., etc.), by the spectral wing of the laser pulse. To our knowledge, the appearance of the side peaks in the ATI spectra has not been yet reported for other atoms such as H, He, and rare-gas atoms, since, according to our interpretation, these side peaks are associated with the real excitation of a certain off-resonant low-lying bound state by the spectral wing of the pulse if the photon energy is in the visible-UV region, which naturally requires a strong single-photon coupling to appear as side peaks in the ATI spectra. That is, the origin of the ATI side peaks of Mg is directly connected to its richer electronic structure; as mentioned above, the first excited state of Mg is located just a few eV above the ground state compared to 19.8 eV for the first excited state of He. Thus, the fact that the multiphoton absorption is required to reach the excited states of He and other rare gas atoms does not allow those states to contribute to the appearance of the side peaks in the ATI spectra. In this paper, we theoretically demonstrate how we could pinpoint the physical origin of the side peaks we have obtained in the numerical ATI spectra.

References: 1. P. Agostini, F. Fabre, G. Mainfray, G. Petite, and N. Rachman,Phys. Rev. A 42, 1127 (1979). 2. Jian Zhang and P. Lambropoulos, Phys. Rev. Lett. 77, 2186 (1996). 3. D.^Xenakis, N. E. Karapanagioti, D. Charalambidis, H. Bachau, and E. Cormier, Phys. Rev. A 60, 3916 (1999).

Corresponding author: Gabriela Buica, e-mail: [email protected], address: Institute for Space Sciences, P.O. Box MG-23, Ro 77125, Bucharest-Magurele, Romania CEE>

Forbidden transitions in excitation by proton impact in Al Li-like ions V. Stancalie', V. Pais'-3, M. Totolici1-2, A. Mihailescu1-2 1National Institute for Laser, Plasma and Radiation Physics, Laser Dept., P.O.Box MG-36 Bucharest, Romania, Association EURATOM MEdC. 2'Politehnica' University, Faculty of Electronics, Telecomm. &1. T., Bucharest, Romania 2Politehnica' University, Automatic Control and Computers Faculty, Bucharest, Romania

Interest in forbidden lines of highly ionized atoms appeared in astrophysics and also in high- temperature laboratory plasmas. In astrophysics, interest in forbidden lines is motivated by the possibility of using them for ion temperature, and density measurements in solar flares and in the solar corona. In laser-produced plasmas, these transitions are mainly responsible for line broadening and lifetimes of the metastable levels. Their measured line intensities and ratios at known electron density may be used to test the adequacy of excitation rates and transition probabilities. Amplification of XUV radiation in plasmas produced by powerful lasers on Al target has been reported [1], Forbidden transitions in excitation by electron impact in Li-like Al ions were been analysed [2] and effective collision strengths obtained [3]. In this paper we present effective collision strengths for forbidden transitions in excitation by proton impact in Li-like Al ions. Results refer to transitions for a single p electron outside closed shells, namely 2p//2- 2pj/2. The impact-parameter formalism as proposed by Burgess and Tully [2] has been used for high energy behaviour calculation. At intermediate energies the cross sections and collision strengths have been evaluated on the use of interpolation in tables provided by Walling and Weisheit [4], The energy levels have been obtained as output from the R-matrix calculation in the case of All()+. The effective target size has been obtained from the calculated high-energy limit of the collision strength in the Born approximation. The upper bound probability has been set as 4/3 in all cases except those for which the interpolation method has been used. In these cases the Seaton' cut-off probability is needed to get correct results.

References [1] Klisnick, A., Sureau, A., Guennou, H, Moller, C.,Virmont, J., Appl.Phys. B50,153-64. [2] Stancalie, V., Burke, V.M., Sureau, A., Phys.Scr.59( 1999)52-54. [3] Stancalie, V., Pais, V., Laser and Particle Beams 24 (2006) in press. [4] Burgess, A., Tully, J.A., J.Phys. B: At. Mol. Opt. Phys. 38(2005)2629-2644; [5] Walling, R.S., Weisheit, J.C., Physics Reports 162(1988) 1-43.

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Revival structure of ionization probability for Rydberg atoms Rita Veilande, Imants Bersons Institute of Atomic Physics and Spectroscopy, University of Latvia, Raina bout. 19, Riga, LV-1586, Latvia

The ionization probability of the one-dimensional Rydberg atom irradiated by two short half- cycle pulses is calculated when the absolute value of the first scaled momentum p1=q/n is small but.v/^/yW2 is large (c/j is the first momentum transferred to the electron), lis/ is small or of the order of unity, only few neighboring states are populated and a typical revival phenomenon is observed [1], For large S/ transitions to many states are involved and the revival phenomena is modified. The approximate expression for the ionization probability is derived:

S (m) = In: rt (1 - + H- - fj) - 2m arctan (f) + 2 [m + r) arctan (^)-rő2, (2)

The first term in equation (1) is the ionization probability averaged over the oscillations. Each term of the r sum is responsible for the oscillations of the ionization probability with the Kepler frequency multiplied by r. Due to the second term of equation (2), the fractional revivals are observed near the time delay z*= kn/(3r),where k= 1,2....

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 Scaled time delay, t

Fig.l. Ionization probability via the scaled time delay: full line - the precise semiclassical theory [2]; dot line - the equation (I) with five terms of r sum, for .v/=-/0, p2=0.9 and the initial state n=100. This work was supported by Latvian Council of Science (Grant 01.0061) and the European Social Fund (ESF).

References [1] I. Bersons and R. Veilande, Phys. Rev. A 69, 043408 (2004). [2] R. Veilande and I. Bersons, J.Phys.B: At.Mo.Opt.Phys. 38, S203 (2005).

Imants Bersons, [email protected] HU1100165 C®

Nonlinear absorption of intense femtosecond laser radiation in molecular gases Kiselev A.M.', Stepanov A.N.1*, Tikhomirov B.A.2, Tikhomirov A.B.2 ' Institute of Applied Physics, 603950, Nizhny Novgorod, U/yanov Str., 46, Russia 2Institute of Atmospheric Optics, 634055, Tomsk, Academichesky Prt., I, Russia

High intensity of femtosecond radiation manifests itself through numerous nonlinear phenomena while propagating in high density molecular gases. One of the most interesting effects, which has been actively investigated for about a decade, is the filamentation of a laser beam propagating in atmosphere. In this paper we present the results of experimental investigation of another nonlinear effect discovered by the authors while studying the propagation of intense femtosecond laser radiation in molecular gases: the nonlinear absorption of energy of laser pulses in the intensity range when ionization is not important yet. Photoacoustic method was used to measure the low absorption of laser radiation. Linearly polarized radiation from a femtosecond laser system (wavelength X 0 =795 nm, spectral bandwidth AA =18 nm, pulse duration FWHM rn =80 fs, repetition rate /**„=10 Hz, pulse energy 2 W < 10 mJ) with Gaussian beam radius a0=4 mm at 1/e level was slightly focused by a spherical mirror with the focal length /= 86.5 cm. A photoacoustic cell with a pressure concentra- tor and a 'A" microphone MK-221 was placed 42 cm from the focusing mirror (center of a cell). The signal from the microphone had the form of a compression wave followed by a rarefaction wave. The dependence of the amplitude of the peak of the acoustic signal on the energy in the femtosecond laser pulse for different molecular gases is shown in Fig. 1. It is a power dependence with power degree exceeding two. In Fig.2 dependence of laser radiation absorption on pulse duration is presented. Model of nonlinear absorption based on the rotational excitation of molecules by linearly polarized ultrashort pulses through the interaction of an induced dipole moment with an electric field is developed. Role of self-focusing of laser radiation will be discussed. The observed nonlinear absorption of intense femtosecond laser radiation can play an important role in the process of propagation of such radiation in atmosphere.

* [email protected] C™D

Heating and ionization of metal cluster by intense femtosecond laser field Kostenko O.F., Andreev N.E. Institute for High Energy Densities, Moscow, Russia

Collisional inverse bremsstrahlung heating, thermal impact ionization and outer field ionization of large metal cluster are analyzed taking into account spatial electromagnetic field structure. Simple analytical expressions for field structure inside and outside of dense uniform cluster, absorption and scattering cross sections are derived in two limiting cases when skin depth ő is considerably greater or smaller than cluster radius R. It is shown that usually used expressions for electric field inside a cluster [1] and corresponding absorption cross-section

<7() are valid only in electrostatic limit when electromagnetic field frequency co~*0. Even in case of ő» R substantial contribution to the cluster heating can be made by induction electric field if module of dielectric permittivity becomes sufficiently large. Using a{) in case of ő « R leads to strong underestimation of absorption cross-section acr In particular, expression for oa is derived in a special case when electron-ion collision frequency essentially exceeds cu and ő « R as some authors [2, 3] believe that in this case absorption cross-section coincides with cluster geometrical cross-section. Note that intensity attenuation depth in a cluster equals to half of skin-depth contrary to some statements [3, 4], Simulations are undertaken with parameters of 1HED femtosecond IR laser complex. It is determined that optimal for heating iron cluster radius equals 20 - 25 nm. As revealed maximum 3/4 electron temperature substantially depends on laser intensity Te ~ /0 and amounts up to 3 keV at 1018 W/cm2. Thermal electrons produce considerable ionization of iron ions L-shell up to formation of Be-like ions. Comparison with an experiment can be made using x-ray bremsstrahlung yield in the range 1 - 2 keV. Criteria of model applicability are under discussion. Coulomb explősion of a cluster and influence of electrons leaving ion core on cluster heating and ionization can be neglected if 2 2 1 » R/rE» \Qco lw , where rE is the amplitude of electron oscillation in laser field, eap is the electron plasma frequency inside a cluster. This work was partly supported by the Russian Foundation for Basic Research (Grant #04-02-17055).

1. DitmireT., Donnelly T., Rubenchik A.M., et al.//Phys. Rev. A. 1996. V. 53. P. 3379. 2. Smirnov M.B., Krainov V.P. // Physica Scripta. 2001. V. 63. P. 157. 3. Smirnov M.B., Skobelev I.Yu, Magunov A.I., et al. // JETP. 2004. V. 98. P. 1123. 4. Krainov V.P., Smirnov M.B. // Physics — Uspekhi. 2000. V. 43. P. 901.

Kostenko Oleg, [email protected]

HU1100166 HU1100167 CpjjT>

Dispersion of femtosecond pulses in vacuum beam lines from ambient pressure down to 0.01 mbar Á. Börzsönyi1, K. Osvay1-2, A. P. Kovács1, M. P. Kalashnikov2 1 Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungaiy 2Max-Born-Institut fiir Nichtlineare Optik und Kurzzeitspektroskopie, Berlin, Germany

In chirped pulse amplification laser systems the laser beam propagates many dozens of meters in air, while the compressed short and high field laser pulses may also travel more tens of meters from the compressor to the target in evacuated beam pipes. The possible dispersion of residual air in the beam pipes may cause undesirable lengthening of the laser pulses just prior to the target. This effect is even more severe for few cycle laser pulses.Thus, the accurate knowledge of air dispersion depending on pressure is of high importance. Although in normal laboratory conditions the modified Edlén's dispersion form [1-2] can be used, but its pressure dependence was deducted from relatively small variations around atmospheric. In this paper we experimentally prove that the pressure dependent part of Edlén's dispersion form is valid for air pressure down to 0.01 mbar. The main experimental apparatus was a spectrally and spatially resolved interferometer, which is basically a Mach-Zehnder interferometer equipped with an imaging spectrograph [3-4], It was illuminated by 800 nm, 18 fs pulses from a Ti:S oscillator working at 71 MHz repetition rate. During the measurements the air conditioning system fixed the room temperature and the relative humidity at 23±1 °C and 35±2 %, respectively. To test our method, first the dispersion of laboratory air at ambient pressure was measured. We have found the specific group delay dispersion (GDD) to be 20.9±1.0 fs2/m, which is extremely close to the theoretical value 20.7±1.2 fs2/m. For the specific third order dispersion (TOD) our measurement gave - I0±I0 fs3/m, while the calculated value is 10±3 fs3/m. Having convicted about the accuracy of the method, the pressure dependence of air dispersion was measured by varying the pressure in a long vacuum tube between 1 bar and 0.01 mbar. To make the method more sensitive, the total spectral phase shift has been also determined from the measurement. As a result, the total phase shift gradually approached zero, that is, to the expected value at perfect vacuum state, and the dependence of GDD on pressure was proved to follow Edlén's form within the error of the measurement. Besides of dispersion compensation, the knowledge of the pressure where the dispersion of air diminishes could also result in less tight vacuum requirement, which can lead to a cost effective beam pipe design and also to shorter maintenance time (faster airing and evacuating). For instance, 20% lengthening of 10 fs, 5 fs and 1 fs pulses upon propagation of 50 m long beam pipes can happen at pressures of 23 mbar, 5.7 mbar, and 0.23 mbar, respectively. This work was supported by OTKA under grant T047078 and NKFP 1/00007/2005.

[1] K.P. Birch, M.J. Downs, Metrologia 31, 315 (1994) [2] S. Lichtenberg, C. Heinisch, V. Petrov, J. Petter, Th. Tschudi, Appl.Opt. 44, 4659 (2005) [3] C. Sainz, J. E. Calatroni, G. Tribillon, Meas.Sci.Technol. 1, 356 (1990) [4] A.P. Kovács, K.Osvay, Z. Bor, R. Szipőcs, Opt.Lett. 20, 788 (1995)

Corresponding Author: Karoly Osvay, [email protected] CP2CT>

Widely tunable ultraviolet sub-30 fs pulses from supercontinuum for transient spectroscopy K. Kosma, S.A. Trushin, W. Fuss, W.E. Schmid Max-Planck-Institut fiir Quantenoptik, Garching, Germany

Short UV pulses are generated using the following two methods: pumping with 800-nm pulses of 45 fs duration FWHM and of energy of 2 mJ, broad-band radiation centred at 800 nm is generated by filamentation and self-phase modulation in argon. By means of chirped mirrors it is compressed to 10 - 20 fs FWHM. Repeating the process with 17-fs pulses as pump pulses supercontinuum radiation is generated, extending from 250 to 1000 nm [1], Spectrally cut out UV parts (around 280, 305 and 320 nm) of the supercontinuum are shortened to < 30 fs FWHM by means of a CaF2 prism compressor. Using bandwidths of ~ 9 nm, the energies obtained were —300 nJ, which is fully sufficient for pumping in ultrafast spectroscopy. The second method is third harmonic generation in argon (pumping by the 800-nm pulses, 17 fs FWHM), using a much shorter gas cell than for the supercontinuum. The UV pulse (270 nm) produced in that way is most probably short (<15 fs) immediately after the tripling cell, but lengthens by GVD after propagating over 3 m in air to the pump-probe experiment, where the pulse length is determined by cross-correlation with the fundamental pulse (signal: ionization yield of Xe or Cr(CO)6 ). The pulses are then recompressed to as short as < 30 fs FWHM, using the CaF2 prism compressor. This seems to be the limit of such a compressor at this wavelength. Shorter pulses would be obtained by better compressing methods or by avoiding the long path in air. This is certainly also valid for the supercontinuum pulses. To demonstrate the applicability in ultrafast spectroscopy, we used the UV pulses as pump and the 800 nm pulses as probe to investigate the dynamics of relaxation and dissociation of + Cr(CO)fv The probe signals are the ion yields of Cr(CO)n . In this multistep process, we found some shorter time constants ( > 12.5 fs ) and higher-frequency coherent oscillations (350 - 450 cm-1) than before [2], but also confirmed the slower processes. We conclude that nonlinear frequency conversion (supercontinuum and third harmonic generation) in gases provides a simple and rugged source of broadly tunable radiation for pumping in ultrafast spectroscopy.

[1] S.A. Trushin et al., Appl. Phys. B 80 (2005) 399. [2] S.A. Trushin et al., Chem. Phys. 259 (2000) 313.

HU1100168 Cp2D HU1100169

Surface-plasmon-ponderomotive electron acceleration as a potential carrier-envelope phase measurement tool P. Dombi', S. E. Irvine2, Gy. Farkas', and A. Y. Elezzabi2 'Research Institute for Solicl-State Physics and Optics, Hungarian Academy of Sciences H-1121 Budapest, Konkoly-Thege M. út 29-33. 2Ultrafast Photonics and Nano-Optics Laboratory, Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada TfiG 2V4

There is a strong motivation among developers of few-cycle femtosecond laser systems to realize a compact carrier-envelope phase (CEP) detector that would enable direct, solid-state- based, single-shot CEP measurement. Such a tool would serve the diagnostics of ultrabright laser systems as well as that of other phase-stabilized femtosecond sources where only some nJs of pulse energy is desired to be sacrificed for on-line phase measurement. Recent advances in understanding light-solid interactions induced by few-cycle pulses [1-3] have not proven sufficient for the construction of a compact, high-contrast phasemeter. Therefore, we propose a new method to overcome this problem and provide new physical insight into surface plasmon-enhanced (SP) electron acceleration, too. We demonstrate, for the first time, that SP electron acceleration can be coherently controlled through the CEP of the excitation pulse (see the fig. for illustration of launching of an SP wave and subsequent dynamics of photo- injected electrons).

It is shown through model calculations that the kinetic energy gain experienced by an electron in the electric field of the SP wave depends intrinsically on the CEP (see figure for overlapped energy spectra of SP-accelerated electrons for CEP ranging from 0 to In and z",„«,,.=5 fs and for the variation of the total number of electrons above A"0=300 eV). Analysis indicates that the physical origin of the CEP sensitivity arises from an electron's ponderomotive interaction with the oscillating electromagnetic field of the SP wave. The underlying mechanism also provides the desired properties required for a high-contrast phasemeter, moreover, the measurement of the CEP of several-cycle pulses (12 fs @ 800 nm in our case) seems also within reach. Further development efforts along the proposed lines could culminate in true waveform synthesis in the optical domain which would provide a tool for ultimate coherent control of atomic, molecular and condensed systems. [1] A. Apolonski, P. Dombi, G. G. Paulus, M. Kakehata, R. Holzwarth, Th. Udem, Ch. Lemell, K. Torizuka, J. Burgdörfer, T. W. Hansch, and F. Krausz, Phys. Rev. Lett. 92, 073902 (2004). [2] T. Fortier, P.A. Roos, D.J. Janes, S.T. Cundiff, R.D. Bhat, J. E. Sipe, PRL 92, 147403 (2004) [3] O.D. Mücke, T. Tritschler, M. Wegener, U. Morgner, F. X. Kártner, G. Khitrova and H. M. Gibbs, Opt. Lett. 29, 2160 (2004). HU1100170 Cp22>

Cubic Phase Control of Ultrashort Laser Pulses K. Mecseki, M. Erdélyi, A. P. Kovács, and G. Szabó Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary

The temporal shape of an ultrashort laser pulse may change upon propagating through a linear dispersive medium having a phase shift ). The change can be characterized by the

Taylor- coefficients of the phase shift which are calculated around the central frequency a>0 of the pulse. Measurements and independent control of the group delay dispersion (GDD,

£?"((%)) and the third order dispersion (TOD, ai0)) are important in several research fields, particularly in the generation of ultrashort laser pulses by chirped pulse amplification (CPA) [1] and pulse shaping for molecular control [2], The GDD and the TOD of an ideal pulse compressor are equal to the negative of the corresponding dispersion coefficients of the medium. However, in the case of prism-pair and grating-pair compressors, which are most often used in laser systems, the ratio of the GDD and the TOD of the compressor is different from the ratio of the coefficients of the medium to be compensated for. Therefore it is necessary to develop so-called cubic compressors that are able to control the TOD of the pulse, yet, do not affect the GDD. In this paper a new cubic compressor setup is investigated theoretically and experimentally, which resembles the set-up proposed by White [3], however, we control the GDD and the TOD by the position of a birefringent, semi-cylinder crystal placed around the focal point of an achromatic lens. For the evaluation of the phase shift introduced by the proposed cubic compressor, a ray tracing program was written. The program allows optimizing the compressor parameters, such as the radius of the crystal, magnification of the lens etc. Calcite was applied because it is a strong birefringent material. Calculations showed that there is a trajectory, along which shifting the crystal the TOD can be tuned independently of the GDD. The value of the TOD changed in a relatively wide range between -3.15-105 fs3 and -1.67-105 fs3. Although the defocus also affects the angular dispersion of the pulse leaving the compressor, it does not exceed the 40 jMrad/nm value. For experimental verification, the cubic compressor was placed in one arm of a Michelson-type interferometer illuminated by a Ti:sapphire oscillator providing 20 fs (FWHM) pulses at a central wavelength of 800 nm. The compressor consisted of a calcite crystal with a radius of 15 mm and an achromatic lens with a magnification of 4 in accordance with the simulation results. The dispersion coefficients of the compressor were determined from the spectrally resolved interferograms (SRI) [4], During the experiments, special attention was paid to minimizing the angular dispersion of the pulse leaving the compressor. The measured GDD and TOD were 3.8 -103 fs2 and -2.6 -10s fs3, while the calculated values were 3.2 -103 fs2 and -1.9-105 fs3, respectively. Taking into consideration the paraxial approximation based simulation, the 25% average error of the dispersion values is acceptable. The simulation results can be used as rough estimation, and SRI can be applied for real-time fine tuning.

1. D. Strickland, G. Mourou, Opt. Commun. 56, 219-221 (1985). 2. H. Rabitz, R. de V-Riedle, M. Motzkus and K. Kompa, Science 288, 824-828 (2000). 3. W. E. White, F. G. Petterson, R. L. Combs, et al., Opt. Lett. 18, 1343-1345 (1993). 4. A. P. Kovács, R. Szipőcs, K. Osvay, Zs. Bor, Opt. Lett. 20, 788-790 (1995).

Corresponding author: Attila P. Kovács, e-mail: [email protected] Carrier-envelope phase measurement of multiterawatt laser pulses T. Wittmann1, M.GSchatzel1, F. Lindner1, GGPaulus'-2-3, A Baltuska1-4, M. Lezius1, A. Marcinvevicius1, F. Tavela1, F.Krausz1-2 ' Max-Planck-lnstitut fiir Qucmtenoptik, 85748 Garching, Germany 2 Ludwig-Maximilians-Universitát München, 85748 Garching, Germany 3 Department of Physics, Texas A&M University, College Station, Texas 77843-4242, USA 4 lnstitut fiir Pliotonik, Technische Universitát Wien, Gusshausstr. 27, A-1040 Wien, Austria

Owing to the recent advances in laser technology, lasers producing ultrashort optical pulses with sub-10 femtosecond duration became widely available. These pulses are so short that they contain only a few oscillation cycles of the electromagnetic field, thus the amplitude of the electromagnetic wave changes almost as rapidly as the field oscillates. As the temporal variation of the field directly governs strong-field interactions, it is of primary importance for any attosecond spectroscopic experiment to measure and control the absolute phase (i. e. the phase of the carrier frequency respect to the envelope) of these few-cycle laser pulses. Our goal is to develop a single-shot stereo-ATI spectrometer based on the expertise that has been recently gained in the invention of a similar multi-shot spectrometer at MPQ. This single-shot device will allow us to measure and as an ultimate goal to control the absolute phase of the emitted laser pulses with pinpoint accuracy. This means that with this device in the future it might become possible to govern the electric field completely to our wish. The stereo-ATI spectrometer will be implemented into a state-of-the-art laser system that is currently at the final stage of development at MPQ. This laser will deliver less than three cycle pulses with <10 TW peak power, which will lead to an unprecedented 1019 W/cm2 intensity at these pulse widths. Controlling the absolute phase of these pulses with the stereo-ATI spectrometer will allow us to generate high intensity single atlosecond pulses by high-order harmonic generation on solid target, which due to its high conversion efficiency has been a desire in laser physics for more than a decade now. With these high-intensity attosecond X- ray bursts it will become possible to gain insight into the motion of electron wavepackets on attosecond time scales.

Corresponding author: Tibor Wittmann Email: [email protected]

HU1100171 HU1100172

Optimization of resonant frequency tripling of KrF laser radiation by gas targets of different lengths R. Rakowski1.2, T. Suta3, l.B. Földes3, S. Szatmári1, J. Bohus1, A. Bartnik2, H. Fiedorowicz2, J. Mikotajczyk2 ' University of Szeged, Department of Experimental Physics, Szeged, Hungary ^ Institute of Optoelectronics, Military University of Technology, Warsaw, Poland KFKI Research Institute for Particle and Nuclear Physics, EURATOM Association, Budapest, Hungary

Previous experiments of Dölle et al. [1] showed the possibility of resonant frequency tripling of KrF laser radiation in argon to 82.8 nm with a conversion efficiency of ~1%. Herewith it is shown that using gas jet targets of several mm lengths it is possible to extend the coherence length of phase-matching, and thus the amplification up to several mm. In the present experiments harmonics conversion efficiency increase was obtained approximately until the geometrical coherence length of 4.4 mm.

We used density-calibrated gas jet targets of 0.65, 3 and 9 mm lengths, aiming to use the theoretical possibility of 4.4 mm geometrical coherence length. Laser pulses of 700 fs were used up to 9 mJ of energy focused by a 1.5 m lens. Gas density was varied by the time delay between opening valve and laser pulse.

It is shown that in the case of low laser intensity, i.e. below 2x1014 W/cm2 intensity, the plasma threshold, the conversion to 3w increases with increasing length of the gas jets, i.e. it is possible to reach the geometrical coherence length as a limit for harmonics generation. The significant growth of 3rd harmonic intensity for 3 mm nozzle ifit compared with the 0.65 mm nozzle case was observed and only slightly increase going from 3 mm to 9 mm nozzle case. Dependences of the 3rd harmonic intensity on the time delay between opening valve and the laser pulse, the backing pressure of gas, the fundamental wavelength tuning, the laser focus position in relation to the nozzle and the laser energy in pulse were investigated. The absolute conversion was in our case however lower than given by Dölle et al. In the present investigations a maximum harmonics energy of 22 fi J was obtained. More precise absolute energy measurements are in progress. For comparison nitrogen instead of argon as a non-resonant medium for 3rd harmonic generation was also used. With increasing laser energy plasma generation is started, the vector mismatching cannot be balanced by the (sometimes) negative contribution of the atomic wave-vector mismatching, therefore the energy of harmonics decreased. These investigations however give evidence that in case of a higher laser energy the conversion rate can be sustained by even smaller F-number focusing, or quasi-parallel propagation using long gas-jet targets.

[1] C. Dölle, C. Reinhardt, P. Simon, B. Wellegehausen, Appl. Phys B. 75, 629 (2002)

Corresponding Author: R. Rakowski, e-mail: [email protected] Attosecond pulse trains from long laser-gas interaction targets C.P. Hauri1, K. Varjú2, T.Ruchon2, E. Gustafsson2, A. L'Huillier2, R. Lopez-Martens' 'Laboratoire d'Optique Appliquée, Ecole Polytechnique-ENSTA-CNRS, F-91761 Palaiseau Cedex, France Phone: +33 169 319733, email:[email protected] 2Department of Physics, Lund University, 221 00 Lund, Sweden

Many experiments in attosecond physics require high XUV photon flux as well as a clean attosecond pulse train (APT) temporal structure. Temporal characterization of high-order harmonic generation (HHG) in long interaction targets is thus of high interest. HHG being a very inefficient process, a large effort has been made to increase the amount of XUV photons emitted per infrared laser pulse. Besides quasi phase-matching in a modulated capillary', loose driving laser focusing conditions and subsequent self-channeling have shown to significantly increase the conversion efficiency2. We characterized the temporal structure of APTs generated during the self-channeling of an intense IR driving laser pulse. Our first results indicate, however, that the temporal structure of the APT generated during the HHG process might be affected by quantum path interference and spectral phase distortion due to the self-channeling process itself. In particular, our measurements show that the relative spectral phase between consecutive harmonics can strongly vary depending on the target length and the position of the laser focus with respect to the target. In general for short gas targets, no clean APT structure can be expected since the individual attosecond pulses carry significant chirp. For longer targets, however, we observe a flattening of the harmonic spectral phase, resulting in near- transform-limited attosecond pulse trains. A complete analysis of the process is complex and involves detailed knowledge of the spatial and temporal evolution of the self-channeling driver laser pulse throughout the gas target.

1. 2. R. Bartels et a!., Nature 406, 164 (2000). 2. H.T. Kim et al., Appl. Phys. B. 78, 863 (2004). 3. H. G. Muller et al., Appl. Phys. B 74, S17 (2002).

HU1100173

szeged 115 (P20

Generation of very high frequency attosecond pulses with precursors E. V. Moiseenko1, P. Martin', G. Farkas2' 'CEA Saclay-DSM-DRECA M-S PA M, France ^ Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, Hungary

After the former idea based on the high harmonic generation spectra [1], we present here a new alternative principle to attosecond pulse generation using the Sommerfeld precursor phenomenon. An oscillating pulse train of finite duration T contains many harmonics separated by 2jt/T. If this train propagates in a dispersive medium, where each frequency travels with a different velocity, after a given propagation length, the frequencies are temporally redistributed. This effect had been studied by Sommerfeld [2] and Brillouin [3] and they showed that high frequency components lying in the X ray band are located well before the front of the main (quasi-monochromatic) signal and that their duration is in the attosecond regime. If the principle seems quite straightforward, the practical realisation of an experiment aiming at the demonstration of this effect needs a lot of care. In particular, the shape of a realistic initial optical laser pulse envelope is of crucial importance to determine the amplitude of generated X rays. If the pulse is Gaussian, even if the effect does exist, its amplitude will be so small that it will not be observable. A pulse with a very sharp edge (namely very small at the optical cycle range) is necessary. Pulses with such approximate shapes are used in the practice [4], In this theoretical work we propose a new technique to determine the properties of such pulses for arbitrarily shaped envelopes. The method is based on the representation of the initial signal as a sum of a number of semi-infinite pulses. The spectra obtained by this method show various effects, such as the "propagation" of high-frequency Fourier components inside the medium and also a cut-off of low-frequency components. The potential possibility of generation of long (picosecond) quasi-monochromatic and ultrashort (sub-femtosecond) pulses with help of precursors is discussed.

[1] Gy. Farkas, Cs. Tóth, Phys. Lett. A, 168, 447 (1992). [2] A. Sommerfeld, Optics (New York, 1954) and also J.D. Jackson, Classical Electrodynamics, second edition. [3] L. Brillouin, Ann Physik 44, 203, (1914) and also L. Brillouin, Wave Propagation and Group Velocity (Academic, New York, 1960). [4] G. Doumy, Quere F, Gobert O, Perdrix M, Martin P, Audebert P, Gauthier JC, Geindre JP, Wittmann T., Phys. Rev. E 69, 26402, (2004).

*e-mail: [email protected]

HU1100174 CptT)

Two-Color Driving In High Harmonic Generation: Single-Atom And Pulse Propagation Analysis Klaus Schiessl1, Emil Persson1, Armin Scrinzi2, and Joachim Burgdörfer1 ' Institute for Theoretical Physics, Vienna University of Technology, Vienna, Austria 2 Photonics Institute, Vienna University of Technology, Vienna, Austria

We consider high-harmonic generation (HHG) with a two-color laser pulse where the admixture of the second laser (intensity I9) is weak compared to the main pulse with 1, , but (nearly) resonant to an atomic excitation. In single-atom calculations, we could confirm the results of Ishikawa [1] obtained for singly-ionized helium, showing a significant enhancement of harmonic output as well as ionization probability. We have performed calculations for hydrogen for which a first-principle treatment is possible and have extended these to rare gas atoms such as xenon and-neutral helium within the Single Active Electron (SAE) approximation. For hydrogen and xenon we have identified a critical intensity of the main pulse above which the resonant enhancement becomes neglible to be roughly 6 - 8x1013 W/cm2 while for singly-ionized helium this critical intensity is larger than 1015 W/cm2. Furthermore, we have investigated the influence of pulse propagation for such resonant two- color pulses. Employing a fully quantum-mechanical pulse propagation scheme based on [2] and neglecting the transverse degrees of freedom we have shown that the enhancement due to a resonant admixture of a second color remains macroscopically intact for short to moderate propagation lengths.

An interesting possibility is to use a two-color pulse in which the second color is not resonant to a one-photon atomic transition, but is rather resonant via a two-photon transition. Colors with such wavelengths can experimentally be generated and handled much more easily than high-frequent colors. For the enhancement to be comparably strong as for a directly resonant second color, however, the admixture fraction relative to the fundamental color has to be much larger compared to the direct resonance. This scheme involving a relatively low-frequency second color may provide an attractive alternative route for experimental realization. We acknowledge support by the Austrian "Fonds zur Förderung der wissenschaftlichen Forschung", under grant no. FWF-SFB016 "ADLIS"'.

[1] K. L. Ishikawa, Phys. Rev. A 70, 013412 (2004). [2] T. Brabec and F. Krausz, Phys. Rev. Lett. 78, 3282 (1997).

Corresponding author: Klaus Schiessl, [email protected]

HU1100175

lfti$Pi29O0-Szegecl. Hungary 117 On the generation of attosecond unidirectional half-cycle pulses: inclusion of propagation effects Emil Persson1, Klaus Schiessl1, Armin Scrinzi2, and Joachim Burgdörfer1 'Institute for Theoretical Physics, Vienna University of Technology, Vienna, Austria 2Photonics Institute, Vienna University of Technology, Vienna, Austria

We have developed a protocol for producing unidirectional half-cycle pulses (u-HCP) in the attosecond regime. HCPs are ideally suitable for shaping, driving, and probing atomic wave packets in momentum space [1], The non-linear harmonic response of atoms to a strong infrared laser field and a small admixture of a frequency doubled component interacting with a gas jet produces odd and even harmonics and opens up the opportunity to form trains of ultrafast HCP's on an attosecond time scale [2]. In the present contribution, we investigate the influence of macroscopic propagation effects on the production of HCPs and show that trains of unidirectional attosecond HCPs can be produced under experimentally realistic conditions. In our simulations, we take both the fully quantum-mechanical single atom response as well as macroscopic propagation effects into account by coupling the solution of the time-dependent Schrödinger equation to Maxwell's equations [3], The propagation is calculated neglecting the degree of freedom transverse to the propagation direction. By carefully choosing the length of the gas target and the parameters of the two-color driving field, the harmonics generated up to the frequency corresponding to the excitation from the ground state to the first excited state can be tuned to what is needed for u-HCPs. The two driving components have to be tuned after the harmonic production to the appropriate intensities and phases. Using a fundamental wavelength of 1064 nm and intensities of the driving field up to 1=1014 W/cm2 interacting with atomic hydrogen, we found trains of u-HCP's with width of each HCP down to 650 as and intensity up to 4.2xl012 W/cm2. Moreover, the gas target dependence was studied within the single active electron approximation for argon, yielding similar results as for hydrogen. The work was supported by the Austrian "Fonds zur Förderung der wissenschaftlichen Forschung", under grant no. FWF-SFB016 "ADLIS"'.

[1] S. Yoshida, C.O. Reinhold, E. Persson, J. Burgdörfer, and F.B. Dunning, J. Phys. B 38, S209 (2005); E. Persson, S. Yoshida, X.M. Tong, C.O. Reinhold, and J. Burgdörfer, Phys. Rev. A 68, 063406 (2003) [2] E. Persson, S. Puschkarski, X.-M. Tong, and J. Burgdörfer, in Ultrafast Optics IV, Springer Series in Optical Sciences, Vol. 95, 253 (2004). [3] T. Brabec and F. Krausz, Phys. Rev. Lett. 78, 3282 (1997).

Corresponding author: Emil Persson, [email protected]

HU1100176 HU1100177 CjvT}

Attosecond Electron Wave Packet Interferometry T. Remetter1, T. Ruchon', P. Johnsson1, K. Varjú1, E. Gustafsson1, R. López-Martens2, M. Kling3, Y. Ni3, F. Lépine3, J. I. Kahn3, M. J. J. Vrakking3, J. Mauritsson1, K. J. Schafer4 and A. L'Huillier1 'Dept. of Physics, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden 2Laboratoire d'Optique Appliquée, Ecole Nationale Supérieure des Techniques Avtmcées (ENSTA) - Ecole Polytechnique CNRS UMR 7639, 91761 Palaiseau Cedex, France IFOM-Institute AMOLF, Kruislaan 407, 1098 S.J Amsterdam, The Netherlands 4 Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 USA

The well controlled generation and characterization of attosecond XUV light pulses provide an unprecedented tool to study electron wave packets (EWPs). Here a train of attosecond pulses is used to create and study the phase of an EWP in momentum space. There is a clear analogy between electronic wave functions and optical fields. In optics, methods like SPIDER or wave front shearing interferometry, allow to measure the spectral or spatial phase of a light wave. These two methods are based on the same principle: an interferogram is produced when recombining two sheared replica of a light pulse, spectrally (SPIDER) or spatially (wave front shearing interferometry). This enables the comparison of two neighbouring different spectral or spatial slices of the original wave packet.

Fig. 1. Experimental interferogram obtained when the EWPs coincide with (a) the minimum (b) the maximum of the vector potential of the IR field.

In the experiment [1], a train of attosecond pulses is focused in an Argon atomic gas jet. EWPs are produced from the single XUV photon ionization of Argon atoms. If an IR beam is synchronized to the EWPs, it is possible to introduce a shear in momentum space between two consecutives wave packets. A Velocity Map Imaging Spectrometer (VMIS) enables us to detect the interference pattern. An analysis of the interferograms will be presented leading to a conclusion about the symmetry of the studied wave packet.

References T. Remetter et al..Nature Physics., (May 2006)

Corresponding author: Thomas Remetter, [email protected]

JAMP12006-SzegetJ, Hungary 119 Application of VUV harmonics light source for investigation of energy transfer mechanisms in the wide band gap solids N. Fedorov, A. Belsky, P. Martin CELIA, University Bordeaux 1, France

The experimental aims were the study of interaction mechanism of excitons generated in the crystals with a wide forbidden gap. For this investigation, we studied the dependence of luminescence from excitation density. As the source of VUV was used high harmonic source based on 1kHz Ti:sapphire 800nm 40fs laser. For our experiments we used harmonics from 15 to 27 generated in Ar (23-42eV).

1. Interaction of molecular excitons in CdW04

CdW04 is the good modeling system with one type of excitations - excitons. It has only one luminescence band, corresponding to Self-Trapped Exciton luminescence. Observation of these experiments is the strong quenching of luminescence at high density of excitation. The mechanism of this quenching is interaction between excitons. The basic interaction mode of electronic excitations is the dipole-dipole interaction. A.Vasiliev has made mathematical model, witch describes this interaction. This model gives the equation to describe the decay kinetics. We can find the parameters of exciton-exciton interaction via fitting measured decay curve data by this equation with known parameters of the crystal and excitation beam.

Result: radius of dipole-dipole interaction of excitons in CdW04 estimated from the fitting:

Rd_d=4.3nm.

2. Interaction of core and valence band excitations in BaF2

BaF9 has two types of localized electronic excitations: Self Trapped Excitons and Auger Free

Luminescence. In contrast to the CdW04 in BaF2 it also presents interaction between excitons and core holes. Experimental evidence: Strong quenching of luminescence at the expense of interaction between core holes and excitons. This interaction is much stronger and faster then exciton- exciton interaction.

HU1100178 List of participants name countrv e-mail address

Andreev, Alexander Russia [email protected] Antoine, Philippe Belgium [email protected] Badziak, Jan Poland [email protected] Baeva, Teodora Germany [email protected] Bakos, Joseph Hungary [email protected] Balcou, Philippe France [email protected] Baranga, Andrei Israel [email protected] Barna, Imre Ferenc Hungary [email protected] Batani, Dimitri Italy [email protected] Boca, Madalina Romania [email protected] Bohus, János Hungary [email protected] Bout'u, Willem France [email protected] Buiea, Gabriela Romania [email protected] Cercliez, Mirela Germany [email protected] Charalambidis, Dimitrios Greece [email protected] Dajka, Rita Hungary [email protected] De Grazia, Marco France [email protected] Deiss, Cornelia Austria [email protected] Desai, Tara Italy [email protected] Dombi, Péter Hungary [email protected] Duchateau, Guillaume France [email protected] Farkas, Győző Hungary [email protected] Fedorov, Nikita France [email protected] Fekete, Júlia Hungary [email protected] Floreseu, Viorica Romania [email protected] Földes, István Hungary [email protected] Förster, Eckhart Germany [email protected] Fülöp, József András Germany [email protected] Gakovic, Bíljana Serbia [email protected] Geissler, Michael Germany [email protected] Ghafur, Omair The Netherlands [email protected] Giulietti, Antonio Italy [email protected] Hatsagortsyan, Karen Germany [email protected] Hauri, Christoph France [email protected] HotTmann, Dieter Germany [email protected] Horváth, Bálint Germany [email protected] Huehon, Christophe United Kingdom [email protected] Jegenyés, Nikoletta Hungary [email protected] Joachain, Charles Belgium [email protected] Johnsson, Per Sweden [email protected] Keitel, Christoph Helmut Germany [email protected] Klimo, Ondrej Czech Republic [email protected] Kling, Matthias The Netherlands [email protected] Kolar, Michal Czech Republic [email protected] Kornev, Alexey Russia [email protected] Kosma, Kyriaki Germany [email protected] Kostenko, Oleg Fedotovieh Russia [email protected] Kovács, Attila Pál Hungary [email protected]

IMSPI2006-Szeged» Hungary 121 List of participants name country e-mail address

Körmendi, Ferenc Hungary [email protected] Krausz Ferenc Germany [email protected] Lein, Manfred Germany [email protected] Lenner, Miklós United Kingdom [email protected] Limpouch, Jiri Czech Republic [email protected] Loch, Rolf The Netherlands [email protected] Lopez-Martens, Rodrigo France [email protected] Major, Zsuzsanna Germany [email protected] Malka, Victor France [email protected] Maquet, Alfred France [email protected] Marangos, Jonathan United Kingdom [email protected] Mauritsson, Johan Sweden [email protected] Mendonca, Jósé Tito Portugal [email protected] Merano, Michele France [email protected] Mercouris, Theodoros Greece [email protected] Mese, Emine Turkey [email protected] Mével, Eric France [email protected] Meyer-ter-Vchn, Jiirgen Germany [email protected] Miaja Avila, Luis United States [email protected] Mirnes, Nawel Algeria [email protected] Mulser, Peter Germany [email protected] Nisoli, Mauro Italy [email protected] Osvay, Károly Hungary [email protected] Ozaki, Tsuneyuki Canada' [email protected] Pais, Vasile Flórian Romania [email protected] Papalazarou, Evangelos France [email protected] Persson, Emil Austria [email protected] ' Pirozhkov, Alexander Japan [email protected] Pirri, Angela Italy [email protected] Rakowski, Rafal Hungary [email protected] Remetter, Thomas Sweden [email protected] Robinson, Joseph S. United Kingdom [email protected] Ruiz Mendez, Camilo Germany [email protected] Rus, Bedrich Czech Republic [email protected] Sagisaka, Akito Japan [email protected] Sali, Emiliano Italy [email protected] Schiessl, Klaus Austria [email protected] Stancalie, Viorica Romania [email protected] Stepanov, Audrey Russia [email protected] Suta, Tibor Hungary [email protected] Szatmári, Sándor Hungary [email protected] Tang, Yunxin United Kingdom [email protected] Thaury, Cedric France [email protected] Tóth, Csaba United States [email protected] Tóth, Zsolt Hungary ztoth@physx. u-szeged .hu Totolid, Marius Cristian Romania [email protected] Trisorio, Alexandre France [email protected] Trtica, Milan Serbia [email protected] List of participants name country e-mail address

Tsakiris, George Germany [email protected] Turcu, Edmond United Kingdom [email protected] Tzallas, Paris Greece [email protected] Ujj, László United States [email protected] Uphues, Thorsten Germany [email protected] Valentin, Constance France [email protected] van der Hart, Hugo United Kingdom [email protected] Varjú, Katalin Hungary [email protected] Varró, Sándor Hungary [email protected] Veilande, Rita Latvia [email protected] Veisz, László Germany [email protected] Villeneuve, David Canada [email protected] Villoresi, Paolo Italy [email protected] Vozzi, Caterina Italy [email protected] Witlman, Tibor Erik Germany [email protected] Wolowski, Jerzy Poland [email protected] Xie, Xinhua Austria [email protected] Yakovlev, Vladislav Germany [email protected] Yamanouchi, Kaoru Japan [email protected] Zepf, Matthew United Kingdom [email protected] Ziaja-Motyka, Beata Germany [email protected] Zvorykin, Vladimir Russia zvory kin@sci. Iebedev.ru

IM1PI2006-Szeged, Hungary 123 Notes viewport® © Spectra-Physics Experience | Solutions A Division of Newport Corporation

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