Danish Physical Society Annual Meeting 2008

Hotel Nyborg Strand Tuesday 17 June - Wednesday June 18, 2008

Programme of DFS Annual Meeting 17-18 June.

Abstracts Sponsors of the DFS/DOPS Annual Meeting 2008

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DTU Nanoteknologi

DTU Fotonik

DTU Fysik

Institut for Fysik og Nanoteknologi, Alborg˚

Niels Bohr Institutet

Institut for Fysik og Astronomi, Arhus˚ Universitet

Institut for Fysik og Kemi, SDU. Contents

Contents 1

Programme 2

Plenary Speaker 13

Astro physics – Cosmology and galaxy formation 19

Astro physics – Extreme astro physics 26

Astro physics – Star and planet formation 27

Atomic Physics 29

Biophysics 37

Condensed matter physics 52

Nuclear and high energy physics 105

Dansk Optisk Selskab 114

1 Programme

Tirsdag 17. juni

11:00 Welcome Plenary session Magic of Flat Carbon (PL1 page 13) 11:15 Andre Geim Chairman: Poul Erik Lindeløf

Plenary session Optofluidics (PL2 page 14) 12:00 Demetri Psaltis Chairman: Anders Kristensen 12:45 Lunch 14:15 Section session I and DOPS 15:45 Coffee, exhibition and posters I

16:45 Section session II and DOPS 18:15 Dinner After-dinner talk The biggest man-made experiment ever: LHC at CERN (PL3 page 15) 20:15 John Renner Hansen Chairman: Jørgen Schou

21:15 Beers, exhibition and posters II

2 Onsdag 18. juni

Plenary session Schr¨odinger’skittens and non-gaussian states of the light : new tools for quantum 9:00 communications (PL5 page 17) Philippe Grangier

Plenary session 9:45 High energy cosmic rays - a new window on the universe (PL6 page 18) Steen Hannestad (and DOPS) Coffee 10:30 (rooms should be left at 11:00)

10:45 Section session III and DOPS generalforsamling

11:30 DFS generalforsamling og DOPS generalforsamling

12:30 Lunch 13:30 Section session IV and DOPS 15:00 Awards Plenary session Wizardry with light ... Now you see it. Now you don’t. Then you see it over there... (PL4 15:15 page 16) Lene Vestergaard Hau Chairman: Jørgen Schou

16:15 End of meeting

3 4 5 6 7 Dansk Optisk Selskabs årsmøde 2008 Hotel Nyborg Strand, 17. og 18. juni 2008

Onsdag den 18. juni 2008

DOPS Generalforsamling 10:45 – 12:15

1. Valg af dirigent 2. Valg af stemmetællere 3. Formandens beretning 4. Valg af formand for 2009 5. Valg af bestyrelsesmedlemmer 6. Valg af suppleanter til bestyrelsen 7. Diskussion af mødeinitiativer i 2009 8. Godkendelse af regnskab for 2007 9. Fremlæggelse af budget for 2008 og 2009 10. Valg af to revisorer 11. Orientering om DOPS NYT 12. Orientering om DOPS’ Web 13. Indkomne forslag 14. Eventuelt

Ifølge DOPS’ vedtægter er formanden på valg hvert år, men kan genvælges. Den nuværende formand (Steen G. Hanson) genopstiller. Bestyrelsesmedlemmer er på valg hvert andet år, og suppleanter til bestyrelsen er på valg hvert år. I år er Kent Mattsson og Kasper Paasch på valg som bestyrelsesmedlemmer. Alle Genopstiller Peter Lichtenberg, Finn Mengel og Mike van der Poel er på valg som suppleanter. Alle tre genopstiller. Andre forslag til opstilling af ny formand eller medlemmer/suppleanter bedes meddelt Steen G. Hanson, (tlf. nr.: 4677 4504, fax nr.: 4677 4565, e-mail ([email protected]) inden den 12. juni 2008. Som revisorer opstilles Torben Jacobsen, Ibsen Photonics, og Mads Sckerl, Grundfos. 12:15-12:45 Uddeling af DOPS’ Juniorpris samt modtagerens præsentation. Program DOPS’ Annual Meeting 2008

Tuesday, June 17. 2008

Plenary Session 11:00 – 12:45

Welcome by The Danish Physical Society 11:00–11:15

Chairman: Poul Erik Lindeløf, NBI, Copenhagen, DK. • Electronic transport in atomically thin carbon films (graphene) (Invited) Andrei Geim, University of Manchester, UK 11:15-12:00

Chairman: Anders Kristensen, Nanotech DTU, DK. • Optofluidics (Invited) Demetri Psaltis, EPFL, Lausanne, Switzerland, 12:00-12:45

Lunch and Exhibition 12:45–14:15

Optics Session I Nano Optics I 14:15– 15:45

Chair: Jørn Hvam, DTU Fotonik • Localized Field Enhancements in Fractal Shaped Periodic Metal Nanostructures :Jonas Beerman et al., Institute of Signals, Sensors and Electrotechnics, University of Southern Denmark 14:15-14:45 • Refracting surface plasmons with nanoparticle arrays: Ilya Radko et al., Department of Physics and Nanotechnology, Aalborg University, Skjernvej 4A, DK-9220 Aalborg Øst, Denmark …………………………………………………………………….. 14:45-15:15 • Wavelength Selective Nanophotonic Components Utilizing Channel Plasmon Polaritons: Valentyn S. Volkov et al.,1Institute of Sensors, Signals and Electrotechnics (SENSE), University of Southern Denmark, Niels Bohrs Allé 1, DK-5230 Odense M, Denmark 15:15-15:45 Coffee, Posters and Exhibition 15:45–16:45

Optics Session II Nano Optics II 16:45 – 18.15

Chair: Martin Kristensen, Aarhus University. • Overrækkelse af DOPS Prisen og modtagerens foredrag 16:45-17:15 • Fractional decay of quantum dots in photonic crystals: Philip Kristensen et al., DTU Fotonik, Department of photonics engineering, Lyngby, DK 17:15-17:45 • Generation of non-classical Surface-Plasmon-Polaritons: Alexander Huck et al., Department of Physics, Technical University of Denmark, Lyngby. 17.45-18:15 Diner 18:15-20:15 Plenary Session 20:15-21:15

Aftenforedrag Chairman: Jørgen Schou, DTU Fotonik, DK.

• The biggest man-made experiment ever: LHC at CERN (Invited): John Renner Hansen, Niels Bohr Institutet 20:15-21:15

Beer, Posters and Exhibition 21:15-??

Wednesday June 18, 2008

Plenary Session 9:00 – 9:45

• Schrödinger's kittens and non-gaussian states of the light: new tools for quantum communications (Invited): Philippe Grangier, Palaiseau, Frankrig 9:00-9:45

Optics Session III General Optics I 9:45 – 10.30

Chair: Henrik Pedersen, DTU Fotonik • Observing of spatial quantum correlations induced by multiple scattering of light: Stephan Smolka et al., DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark. 9:45-10:05 • Three-dimensional imaging and three-dimensional coordinate gathering in three-dimensional optical micromanipulation system: Jeppe Seidelin Dam et al., Danish Technical University Fotonik, Department of Photonics Engineering, Roskilde, Denmark 10:05– 10:30

Posters og kaffe 10:30–10:45

General Assembly for The Danish Optical Society 10.45-12:15

• The Junior Award for The Danish Optical Society, and the award- winners lecture 12:15-12:45

Lunch 12:45-13:30

Optics Session IV General Optics II 13:30-15:00

Chair: Preben Buchhave, Department of Physics, Technical University of Denmark, Lyngby • Principles and applications of a speckle-based wavefront sensor: Percival F. Almoro et al., Danish Technical University Fotonik, Department of Photonics Engineering, Roskilde 4000, DK 13:30-14:00 • Correlation measurement of squeezed light: L. A.Krivitsky et al., Department of Physics, Technical University of Denmark, Lyngby, Denmark and Max Plank Research Group, University of Erlangen Nurnberg, 91058 Erlangen, Germany 14:00-14:30 UV assisted rotational moulding of microstructures for high-volume production of diffractive optical elements on foil: Lars R. Lindvold and Jan Stensborg Stensborg A/S Frederiksborgvej 399, Niels Bohr, 4000 Roskilde, Denmark. 14:30-15:00

Plenary Session 15:00-16:15

Poster Awards 15:00-15:15

Chairman: Jørgen Schou, DTU Fotonik, DK. Wizardry with light ... Now you see it. Now you don't. Then you see it over there... (Invited): Lene Vestergaard Hau , Harvard University, Cambridge, Massachusetts, USA 15:15-16:15 Termination 16:15 Abstracts

12 Plenary Speaker

PL1 Magic of Flat Carbon

By Andre Geim University of Manchester, UK First found in 2004 graphene is now one of the brightest stars on the horizon of materials science and condensed matter physics, revealing a cornucopia of new physics. I will overview our experimental work on graphene concentrat- ing on its next-to-magic electronic and optical properties and speculate about future applications.

13 PL2 Optofluidics

By Demetri Psaltis 1EPFL, Lausanne, Switzerland 2Caltech, Pasadena, USA

Optofluidics refers to a class of adaptive optical circuits that integrate optical and fluidic devices. Familiar examples include liquid crystals and dye lasers. The introduction of liquids in the optical structure enables flexible fine-tuning and reconfiguration of circuits so they can perform tasks optimally in a changing environment. I will discuss how the emergence of fluidic transport technologies at the micron and nanometer levels opens possibilities for novel adaptive optical devices.

The integration of microfluidic circuits with photonic structures that contain voids into which fluids are injected and the use of colloidal solutions of nanoparticles are some of the approaches being pursued. Electrical fields or light beams redistribute the nanoparticles and modify the optical properties of the structure. Liquid dyes injected into microfluidic chips provide the optical gain necessary for building a dye laser on a chip.

14 PL3 The biggest man-made experiment ever: LHC at CERN

By John Renner Hansen The Niels Bohr Institute Blegdamsvej 17, DK-2100 Copenhagen Ø

The Large Hadron Collider at CERN will soon begin operation and deliver protons-proton collisions and heavy ion collisions at energies never made available for experiments before. Thispresentation aims to give an overview of the experimental programme at the LHC, where two Danish groups from the Niels Bohr Institute have contributed to the design and construction of central components to the experiments ATLAS and ALICE. Monte Carlo simulations based on various theoretical models will be presented to exemplify the discovery potential of the four main experiments and to illustrate why and how the experiments had to push state-of-the-art technologies in order to reach sufficient sensitivity.

15 PL4 Wizardry with light ... Now you see it. Now you don’t. Then you see it over there...

By Lene Vestergaard Hau Mallinckrodt Professor of Physics and of Applied Physics Lyman Laboratory Harvard University 17 Oxford Street Cambridge, Massachusetts 02138, USA

Light pulses have been slowed in Bose-Einstein condensates to a few meters per second, eight orders of magnitude lower than the light speed in vacuum. Associated with the dramatic reduction factor for the light speed is a spatial compression of the pulses by the same large factor. A light pulse, which is 1 mile long in vacuum, is compressed to a size of only 20 microns, and at that point it is contained within the condensate.∼ This further allows the light pulse to be completely stopped and stored in the atomic medium and later regenerated.

In our most recent experiments, a light pulse is stopped and extinguished in one part of space and then revived and sent back on its way at a different location. In the process, a matter imitation of the light pulse travels between the two locations, and at the revival position, the matter copy is converted back to light. Matter, as opposed to light, is easily manipulated, and changes induced in the matter copy are transferred to the revived optical pulse. The work demonstrates a powerful new method for coherent processing of optical information and has applications in optical computing and quantum information processing as well as for controlled sculpting of atomic wavefunctions.

16 PL5 Schr¨odinger’skittens and non-gaussian states of the light : new tools for quantum communications

By Philippe Grangier Laboratoire Charles Fabry de l’Institut d’Optique, F-91127 Palaiseau, France

We describe recent experiments [1, 2, 3] manipulating the quantum state of femtosecond light pulses, in order to generate photon number states (Fock states with n= 1 or 2 photons), quantum superpositions of coherent states (Schr¨odinger’scats and kittens [1,2]), and non-gaussian entangled states [3]. We will also discuss possible applications of these new states for quantum communications.

[1] A. Ourjoumtsev et al., ”Generating optical Schr¨odingerkittens for quantum information processing”, SCIENCE 312: 83-86 (2006 ) [2] A. Ourjoumtsev et al., ”Generation of optical ”Schr¨odingercats’ from photon number states”, NATURE 448: 784-786 (2007) [3] A. Ourjoumtsev et al. ”Increasing entanglement between Gaussian states by coherent photon subtraction”, PRL 98:030502 (2007)

17 PL6 High energy cosmic rays – a new window on the universe

By Steen Hannestad University of Aarhus Observations of ultra-high energy cosmic rays are currently opening a new window on the Universe. There is now substantial evidence that these particles are emitted close to the massive black holes in active galaxies, and cosmic ray observations therefore provide a unique opportunity to study some of the most exotic objects in our Universe. Measurements of cosmic rays at very high energies also have the potential to probe such diverse phenomena as new physics beyond the standard model, dark matter and the large scale magnetic fields between galaxies.

18 Astro physics – Cosmology and galaxy formation

AC1 Non-perturbative particle production from SUSY flat directions – a spoiler of delayed thermalisation?

By Anders Basbøll University of Arhus˚ Non-perturbative particle production from SUSY flat directions – a spoiler of delayed thermalisation?

The (possible) existence of Supersymmetry changes (p)reheating of the Universe. In the minimal SUSY (MSSM) there are more than 300 flat directions – directions in field space with vanishing potential. One or more of these can develop Planck-size vacuum expectation values during inflation. This will give high masses to MSSM particles, thus delaying thermalisation and lowering the reheating temperature, providing a solution to the gravitino problem – the problem that gravitinos are not widespread, which would otherwise be expected.

However, all this depends on the flat directions being able to store energy long enough before they decay. This will not happen if the flat direction can decay through a parametric resonance – a process known as preheating.

Earlier studies have either been on toy models, or “rule-of-thumb”-based. I have done a full calculation of actual MSSM flat directions in the unitary gauge to get rid of unphysical goldstone particles. I found that for the 2 most cosmological attractive directions, UDD,LLE there is no particle production – not even with both directions combined. But QLQLQLE will produce particles, the same will QLD+LLE directions existing simultaneously.

19 AC2 Neutrino mass determination with Bayesian statistics

By Anna Sejersen Riis 1 and

Steen Hannestad1 Christian Weinheimer2

1Institute for Physics and Astronomy, Aarhus University 2Institute of Nuclear Physics, Westf¨alischeWilhelms-Universit¨at, M¨unster The search for the neutrino mass is currently taking place using either cosmology, neutrino-less double beta decay or ordinary beta-decay. The KATRIN experiment plan to use the Tritium beta-spectrum endpoint to determine the mass of the neutrino with a sensitivity of 0.2eV. The Analysis of the data from KATRIN will naturally require a lot of consideration. The earlier analysis of the Mainz experiment was performed using frequentist methods. Specifically the minimization code Minuit, now an integrated part of ROOT. However if one wishes to investigate the KATRIN data for e.g. non-standard couplings to righthanded and sterile neutrinos, this approach is not very efficient. For fitting of many parameters one can instead use Markov Chain Monte Carlo methods to reliably probe multi-parameter spaces. This is a Bayesian analysis tool widely used in cosmology. We are using the COSMOMC package with simulated KATRIN data to extract neutrino mass bounds and to probe the sensitivity for new neutrino physics.

20 AC3 Gamma Ray Bursts as probes: a status report

By J. P. U. Fynbo 1 and on behalf of a larger GRB collaboration

1 Dark Cosmology Centre, Niels Bohr Institute, Copenhagen University Gamma-ray bursts (GRBs) constitute a powerful probe of high-z galaxies. GRBs allow us to localize high-z galaxies that, due to their faintness, are extremely difficult if not impossible to localize with other methods. Moreover, spec- troscopy and imaging of the afterglows of GRBs provide a wealth of information on the state of chemical enrichment, dust content, and internal kinematics of high-z galaxies. The currently operating Swift satellite has given the field a tremendous boost due to its frequent, very rapid, and precise localisations of, on average, more distant GRBs than previous GRB missions. In this talk I give a short review of the most important conclusions that we in my opinion have made from the last 3 years of optical follow up of Swift GRBs and their host galaxies.

21 AC4 On the properties of galaxies hosting GRBs... from an IR point of view

By Jos´eMar´ıaCastro Cer´on 1, and

MichalJerzy Michalowski 1, Jens Hjorth 1, Daniele Malesani 1, Javier Gorosabel 2, Darach Watson 1, Johan Peter Uldall Fynbo 1

1 Dark Cosmology Centre, Niels Bohr Instituttet, Københavns Universitet, 2 Instituto de Astrof´ısica de Andaluc´ıa,Consejo Superior de Investigaciones Cient´ıficas The detection of a gamma ray burst (GRB) is a clear indication that its host galaxy harbours massive star for- mation. It is currently under debate how GRB hosts relate to other known populations of star forming galaxies. Multiwavelength photometry can help establish this relation, essential if we are to understand the full range of proper- ties of star forming galaxies at high redshifts and fully exploit the potential of GRBs as probes of cosmic star formation.

I have used Spitzer data to derive the properties (star formation rate, total stellar mass, intrinsic extinction, and physical evolution) of a sample of GRB host galaxies. I found them to be low mass, star forming systems and, when compared to other types of star-forming galaxies, the hosts of GRBs have some of the highest specific star formation rates.

In the course of my presentation I will briefly discuss my methodology and highlight the most important results of my research. I will also give a quick overview of my immediately upcoming projects to further this line of work.

22 AC5 Measurement of the dark matter velocity anisotropy profile in galaxy clusters

By Ole Høst Dark Cosmology Centre, NBI, University of Copenhagen The internal dynamics of a dark matter structure may have the remarkable property that the local temperature in the structure depends on direction. This is parametrized by the velocity anisotropy β which must be zero for relaxed collisional structures, but has been shown to be non-zero in numerical simulations of dark matter structures. We present a method to infer the radial profile of the velocity anisotropy of the dark matter halo in a galaxy cluster from X-ray observables of the intracluster gas. This non-parametric method is based on a universal relation between the dark matter temperature and the gas temperature which is confirmed through numerical simulations. We apply this method to observational data and we find that β is significantly different from zero at intermediate radii. Thus we find a strong indication that dark matter is effectively collisionless on the dynamical time-scale of clusters, which 2 1 implies an upper limit on the self-interaction cross-section per unit mass σ/m . 1cm g− . Extrapolating our analysis to radii smaller than what can be probed by numerical simulations at present, we find observational indications that β increases to about 0.3.

23 AC6 Cleaning up the mess of Abell 1689

By Signe Riemer-Sørensen Dark Cosmology Centre The cluster of galaxies Abell 1689 is mostly known for its large number of multiply lensed images of background galaxies, which allows to map the cluster mass with weak and strong gravitational lensing. Another measure of the mass comes from the hot intracluster X-ray emitting gas. The temperature and mass profiles have been obtained from an analysis of all existing X-ray data of Abell 1689. The X-ray analysis reveals some structure in the cluster, which can explain some of the disagreement between the mass profiles from lensing and X-ray.

24 AC1P Cleaning up the mess of Abell 1689

By Signe Riemer-Sørensen 1 and

D. Paraficz 1, D.D.M. Ferreira 1, K. Pedersen 1, M. Limousin 12, H. Dahle 3

1 Dark Cosmology Centre, Niels Bohr Institute 2 Laboratoire d’Astrophysique de Toulouse-Tarbes, Universit´ede Toulouse 3 Institute of Theoretical Astrophysics, University of Oslo The cluster of galaxies Abell 1689 is mostly known for its large number of multiply lensed images of background galaxies, which allows to map the cluster mass with weak and strong gravitational lensing. Another measure of the mass comes from the hot intracluster X-ray emitting gas. The temperature and mass profiles have been obtained from an analysis of all existing X-ray data of Abell 1689. The X-ray analysis reveals some structure in the cluster, which can explain some of the disagreement between the mass profiles from lensing and X-ray.

25 Astro physics – Extreme astro physics

AE1 Signature of deconfinement during spin down in cooling neutron stars

By Morten Stejner 1 and

Fridolin Weber 2 Jes Madsen 1

1 Department of Physics and Astronomy, University of Arhus˚

2 Department of Physics, San Diego State University The state of matter in neutron star cores at densities beyond nuclear saturation is highly uncertain and may involve a phase transition to quark matter – a deconfined phase in which up, down and strange quarks are the relevant degrees of freedom. The thermal evolution of neutron stars provides valuable information on the state of matter in their interiors and understanding it will therefore help constrain fundamental elements of nuclear and particle physics. We explore the coupling between spin down and cooling for neutron stars which undergo a phase transition to deconfined quark matter at the high densities present in stars at low rotation frequencies. We find that the introduction of a pure quark matter phase in the core delays the cooling and produces a period of increasing surface temperature for strongly superfluid stars of strong and intermediate magnetic field strength.

26 Astro physics – Star and planet formation

AS1 Asteroseismology with Kepler and SONG

By T. Arentoft 1 and

H. Kjeldsen 1 J. Christensen-Dalsgaard 1 F. Grundahl 1 C. Karoff 1

1 Department of Physics and Astronomy, University of Aarhus Kepler is a NASA satellite mission scheduled for launch in February 2009. The aim of the mission is to detect transiting extrasolar planets; however the long, uninterrupted time-series observations will also provide a unique data set for asteroseismology, the use of stellar oscillation frequencies to probe the interior of the stars. After a brief overview of the Kepler mission, the Kepler Asteroseismic Investigation, which is organized at University of Aarhus, will be described. We will also describe the SONG project, which is a global network of 1-m class telescopes for asteroseismology and planet finding and for which the prototype is under development at University of Aarhus and Copenhagen University. We give an account of the aims of the network and describe the current status.

27 AS1P SONG – Stellar Observations Network Group

By Frank Grundahl[1] and

Jørgen Christensen-Dalsgaard1, Torben Arentoft1, Søren Frandsen1, Uffe Graae Jørgensen2, Hans Kjeldsen1, Per Kjærgaard Rasmussen2 Affiliations: 1 Danish AsteroSeismology Centre, Department of Physics and Astronomy,University of Aarhus, DK-8000 Aarhus C, Denmark 2 Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen,Denmark

Several areas of stellar observations depend critically on nearly continuous observations of individual objects over very extended periods.Important examples are investigations of stellar oscillations to carry out asteroseismology, and the search for extra-solar planets. To meet this requirement we are establishing the SONG network, consisting of 8 1-meter-class telescopes with a suitable geographical distribution. These will be optimized for asteroseismology based on Doppler-velocity observations and the characterization of extra-solar planets with photom- etry, using gravitational microlensing. Funding has been obtained towards the construction of the prototype SONG telescope which will be set up on Tenerife, with first light expected in 2011. The full network will be established in parallel with the tests of the prototype and is planned to be operational in 2014.

28 Atomic Physics

AF1 Frequency ratio of the Al+ and Hg+ single-ion optical clocks; metrology at the 17th decimal place

By Anders Brusch 1,2 and

T. Rosenband 2 D. B. Hume 2 P. O. Schmidt 3 C. W. Chou 2 L. Lorini 4 W. H. Oskay 5 R. E. Drullinger 2 T. M. Fortier 2 J. E. Stalnaker 6 S. A. Diddams 2 W. C. Swann 2 N. R. Newbury 2 W. M. Itano 2 D. J. Wineland 2 J. C. Bergquist (2

1 Niels Bohr Institute 2 National Institute of Standards and Technology, Boulder, CO, USA 3 Institut fur Experimntalphysik, Universitat Innsbruck, Austria 4 Istituto Nazionale di Recerca Mertologica (INRIM), Torino, Italy 5 Stanford Research Systems, Sunnyvale, CA, USA 6 Department of Physics and Astronomy, Oberlin College, Oberlin, OH, USA The high performance of atomic clocks based on microwave transitions is a critical element of satellite navigation systems and very long baseline interferometry in radio astronomy. Recently, a regime of operation for atomic clocks based on optical transitions has become possible, promising even higher performance from the division of time into elements that are smaller by a factor 100 000. Here we report the frequency ratio of the two most accurate and stable atomic clocks in the world with a total fractional uncer- 17 tainty of 5.2 10− . The ratio of aluminium and mercury single-ion optical clock frequencies νAl+/νHg+ is 1.052871833148990438(55),× where the uncertainty comprises a statistical measurement uncertainty of 17 17 17 4.3 10− , and systematic uncertainties of 1.9 10− and 2.3 10− in the mercury and aluminium frequency standards,× respectively. This frequency ratio is the× best known physical× constant that is not a simple integer. Repeated measurements during the past year yield a preliminary constraint on the temporal variation of the fine- 17 structure constant of dα/α = ( 1.6 2.4) 10− /year. − ± ×

29 AF2 Turbulence and transport in fusion plasma

By Anders H. Nielsen [1] and

Jens Juul Rasmussen [1], Volker Naulin [1], Jens Madsen [1] and Odd-Erik Garcia [2]

[1] PLF, Risø National Laboratory for Sustainable Energy DTU, DK-4000 Roskilde [2] Department of Physics and Technology, University of Tromsø, N-9037 Tromsø, Norway

Turbulent transport is the dominating mechanism for plasma transport across a confining magnetic field in hot plasmas. This transport is usually referred to as anomalous transport in contrast to normal (classical/neo-classical) transport mediated by collisions. It is the limiting factor for plasma confinement in fusion plasma experiments and an important mechanism for mixing and transport in space plasmas. The turbulent fluctuations arise spontaneously due to pressure gradients perpendicular to the magnetic field. Low frequency plasma turbulence is well described by the fluid model for plasma dynamics, and it is essentially quasi two-dimensional, i.e., the turbulence is strongly anisotropic with the main dynamics in the plane perpendicular to the magnetic field. In this talk I will at introduce the specific features of plasma turbulence and the associated transport/mixing. As a specific example I will discuss turbulence in the boundary region (edge plasma) and scrape-off layer (SOL) region of magnetically confined plasmas, where the relative fluctuation levels in, e.g., the plasma density approach unity.

30 AF3 Core-level spectroscopy with high-order harmonics as a source

By Bjarke Christensen and

Peter Balling

Department of Physics and Astronomy, University of Aarhus, Ny Munkegade bldg. 1520, DK-8000 Aarhus C Time-resolved studies of dynamical processes on surfaces can provide new insight into the physical mechanisms. In order to facilitate this the probe must be sufficiently short compared to the characteristic time-scale of the problem un- der investigation. Such short probes have been achieved with optical femtosecond pulses and pump-probe experiments on valence electrons have been reported. Due to the delocalized nature of the valence electrons they are relatively insensitive to structural dynamics, so structure may be more suitably studied by the much more localized core-levels.

An experimental setup has been realized where femtosecond pulses with a photon energy of 65 eV has been gen- erated by high-order harmonic generation and applied to perform spectroscopy on the bismuth 5D core-levels.

This leads to future perspectives of pump-probe experiments on core-levels which can be applied to study phenomena as diverse as desorption processes and coherent lattice vibrations.

31 AF4 Probing isotope effects in chemical reactions using single ions

By Klaus Højbjerre 1 and

Peter F. Staanum 1 Roland Wester 2 Michael Drewsen 1

1 Department of Physics and Astronomy, University of Aarhus 2 Physikalisches Institut, Universit¨atFreiburg Isotope effects often play an important role for the outcome of chemical reactions. For instance the chemical com- position of interstellar clouds is strongly influenced by isotope effects in certain reactions. In laboratory experiments, Isotope effects observed in isotopic analogs of chemical reactions can provide important information about details of the reaction dynamics.

+ 2 Here we present a recent study of isotope effects in reactions between Mg in the 3p P3/2 excited state and molecular hydrogen at thermal energies, through single reaction events observed in a Paul trap. From only 250 reactions with HD, the branching ratio between formation of MgD+ and MgH+ is found to be larger than 5. ≈

Our study shows that that few singleion reactions can provide quantitative information about branching rations and relative reactions rate coefficients in ion-neutral reactions. Hence the method is particularly well suited for reac- tion studies involving rare species, e.g., rare isotopes or short-lived unstable elements, as well as for studies involving state prepared molecular ions, more complex molecular ions or ions of astrophysically relevant reactions.

32 AF5 Cavity-QED with ion Coulomb crystals

By Peter Herskind and

Aurelien Dantan, Joan Marler, Magnus Albert, Michael Drewsen

Danish National Research Foundation Center for Quantum Optics – Quantop Department of Physics and Astronomy The University of Aarhus Cavity quantum electrodynamics (CQED) provides for the study of light-matter interaction at the level of single quanta. Experimental progress, within recent years, has made it possible to trap even single atoms inside small optical cavities making the coherent process of photon-atom coupling faster than any dissipative processes, such as sponta- neous emission and cavity decay. In this so-called strong coupling regime, CQED holds great promise as a tool for quantum information science where an efficient light-matter interface is in high demand for many applications.

Clouds of cold ions represent an interesting alternative system to a single atom/ion for studying CQED effects. When a trapped cloud of ions is cooled below a certain critical temperature, the ions form a spatially ordered state, known as an ion Coulomb crystal. We have succeeded in trapping and cooling such ion Coulomb crystals inside a high finesse optical cavity. The number of ions in the cavity mode is sufficient for the collective coupling of the ions to a single cavity photon to exceed both the spontaneous and the cavity decay rates, and we have recently seen the first signals of a strong collective coupling in this system, most dramatically manifested via the vacuum Rabi splitting.

33 AF6 Investigation of Plasma Effects in Ultra High Molecular Weight Polyethylene (UHMWPE) Cords

By Steluta Teodoru 1 and

Yukihiro Kusano 1, Noemi Rozlosnik 2 and Poul K. Michelsen 1

1Optics and Plasma Research Department, Risø National Laboratory for Sustainable Energy Technical University of Denmark, DK-4000 Roskilde, Denmark 2Department of Micro- and Nanotechnogy, Technical University of Denmark, DK-4000 Roskilde, Denmark

Ultra-high-molecular-weight polyethylene (UHMWPE) has been widely used because of its high chemical stabil- ity, high impact strength, flexibility and low cost. Its field of applications includes use in composites, packing for microelectronic components and biomaterials, usually requiring its surface modification for improved wetting and/or adhesion with other polymeric materials. Atmospheric pressure plasma treatment is promising for this purpose due to its environmental compatibility, high treatment effects without affecting the textural characteristics of the bulk material, its applicability to a variety of shapes, and easy up-scaling and construction of in-line production processes. An atmospheric pressure dielectric barrier discharge (DBD) plasma is used to study surface modification effect on UHMWPE cords, operated at a frequency of ca. 40 kHz in He, He/O2, O2 and N2 gases. The cords were continuously treated by the plasma with an exposure time of 5-20 s. The plasma is diagnosed by optical emission spectroscopy, while the treated UHMWPE cords are characterized using Fourier transform infrared spectroscopy, core and valence-band X-ray photoelectron spectroscopy (XPS), and atomic force microscopy. Core XPS results indicate the formation of carboxylic (COOH, COOR), carbonyl (C=O), ether (C-O-C) epoxide (cyclic ether), acetal (O-C-O) and hydroxylic (OH) groups at the surface after the treatment, but can not quantitatively distinguish between epoxide and hydroxilic groups. Valence-band XPS spectra are more sensitive to the differences in the surface functionality than core region spectra, being a useful tool for the estimation of the epoxide and hydroxylic group concentrations at the surface. The surface modification mechanism will be extensively discussed in terms of the plasma conditions, referring the application for adhesion improvement.

34 AF1P The hardwater reservoir effect in radiocarbon dating

By Bente Philippsen 1 and

Henrik Kjeldsen 1 S¨onke Hartz 2 Harm Paulsen 2 Ingo Clausen 3 Jan Heinemeier 1

1 AMS 14C Dating Centre, University of Aarhus 2 Arch¨aologisches Landesmuseum, Schloss Gottorf 3 Arch¨aologisches Landesamt Schleswig-Holstein, Außenstelle Neum¨unster Reservoir effects are a common error source in radiocarbon (14C) dating when the carbon in the sample comes from another reservoir than the atmosphere. The hardwater effect is the reason for spurious, too high radiocarbon ages found with samples that were formed in freshwater systems with a high content of dissolved carbonate. This can affect water plants and fish, but also for example humans that ate freshwater fish.

The dating of food crusts on Stone Age pottery from Northern Germany yielded surprisingly high ages. As the pottery was found next to hardwater rivers, it was suspected that the preparation of freshwater fish caused the high radiocarbon ages of the food crusts in the pots. This assumption had been tested by the dating of ancient and modern samples of both terrestrial and fluvial origin.

The small sizes of for example fish bone and food crust samples necessitated advancement in sample preparation. I will present some promising approaches that can make the preparation of very small samples more accurate and efficient. The focus is on the extraction of graphite from the samples, the form, in which the 14C content can be measured by accelerator mass spectrometry.

35 AF2P Pulsed laser deposition of TiO 2 on MgO studied by RHEED

By I L Rasmussen 1 and

N Pryds 2 J Schou 1

1 Department of Photonics Engineering, Risø Campus, Technical University Denmark – DTU, 4000 Roskilde 2 Fuel Cells and Solid State Chemistry Department, Risø DTU, Technical University Denmark – DTU, 4000 Roskilde

Reflection high-energy electron diffraction (RHEED) operated at high vacuum pressure has been used to monitor the growth of thin films of titanium oxide (TiO 2) deposited on magnesium oxide (MgO) substrates. Thin films of TiO 2 have been deposited on (100) MgO by pulsed laser deposition (PLD) with targets of pure titanium dioxide. The topography and structure of the deposited thin films have been investigated in-situ with RHEED, and ex-situ with X- ray diffraction (XRD) and atomic force microscopy (AFM). The growth mode of the films has been determined based on the RHEED, XRD and AFM observations. The growth will be discussed and compared to previously obtained results with titanium nitride (TiN) grown on (100) MgO.

36 Biophysics

BF1 The NF-kB signaling system

By Benedicte Mengel and

S. Krishna M. H. Jensen

Niels Bohr Institute, Copenhagen NF-kB is a protein present in human cells, involved in many processes such as immune response, inflammation, cellular growth, survival and apoptosis. Additionally, it is active in a large number of diseases, including cancer, heart diseases and asthma.

The NF-kB signaling system is known to transcribe more than 150 genes, but how the gene specificity is obtained remains unclear.

We propose a simplified system of the NF-kB network including all three inhibitor proteins of NF-kB. The model is found to exhibits the experimentally observed features of the signaling system. Furthermore we work on understanding how the degrading IKK kinase signal is modified by a possible negative feed- back from NF-kB transcribed proteins.

37 BF2 Qualitative Mapping of Structurally Different Polypeptide Nanotubes

By Casper Hyttel Clausen 1 and

Jason Jensen 2 Jaime Castillo1 Maria Dimaki 1 Winnie Edith Svendsen 1

1 DTU Nanotech – Department of Micro and Nanotechnology, Technical University of Denmark, DK-DK – 2800 Kongens Lyngby, Denmark 2 School of Physics, Trinity College Dublin, Dublin 2, Ireland Uncovering the physical properties of biological structures is a field yet to be explored. For example the genetic information stored in the human chromosomes is now mapped and can be accessed by everyone through the human genome project. However, practically no data exists on the physical parameters of these structures, such as size, dielectric properties and charge, information which is necessary in order to get an idea of the existing possibilities for controlled manipulation.

Electrostatic force microscopy (EFM) investigations were carried out in air on β-amyloid polypeptides tubes placed on pre fabricated SiO2 surfaces with a backgate. The point of the investigation was to estimate the dielectric constant of the peptides in order to use it for microfluidic device optimization. Also EFM measurements on solid and silver filled peptides were carried out for comparison. The phase shift caused by the electrostatic forces, together with geometrical measurements of the AFM cantilever and the polypeptides were used to estimate a value for the dielectric constant of different polypeptides.

38 BF3 Single-molecule observation of topotecan-mediated TopIB activity at a unique DNA sequence

By Fabian Czerwinski 1 and

Ludovic Halby 2, Daniel A. Koster 3, Aur´elienCrut 3, Paola B. Arimondo 2, Nynke H. Dekker 3

1 Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark 2 CNRS, Paris, France 3 Kavli Institute of Nanoscience, University of Technology Delft, The Netherlands The rate of DNA supercoil removal by human topoisomerase IB (TopIB) is slowed down by the presence of the camptothecin class of antitumor drugs. By preventing religation, these drugs also prolong the lifetime of the covalent TopIB–DNA complex. Here, we use magnetic tweezers to measure the rate of supercoil removal by drug-bound TopIB at a single DNA se- quence in real time. This is accomplished by covalently linking camptothecins to a triple helix-forming oligonucleotide that binds at one location on the DNA molecule monitored.

Surprisingly, we find that the DNA dynamics with the TopIB–drug interaction restricted to a single DNA sequence are indistinguishable from the dynamics observed when the TopIB–drug interaction takes place at multiple sites. Specifi- cally, the DNA sequence does not affect the instantaneous supercoil removal rate or the degree to which camptothecins increase the lifetime of the covalent complex. Thus, the dissociation of the covalent complex is a Poisson process with a characteristic time in the order of a few minutes not altered by DNA sequence. We can also confirm that the increased friction of the rotating DNA strand inside the enzymatic cavity in the presence of camptothecin leads to an accumulation of positive supercoils.

Our data suggest that sequence-dependent dynamics need not to be taken into account in efforts to develop novel camptothecins.

39 BF4 Photonics workstation for optical manipulation

By Ivan R. Perch-Nielsen and

Jeppe S. Dam, Darwin Palima and Jesper Gl¨uckstad

DTU Fotonik, Department of Photonics Engineering Frederiksborgvej 399, P.O.49, DK-4000 Roskilde, Denmark

Optical forces have established a track-record of non-contact handling of micro particles and cells suspended in flu- idic environments. We have extended this tool with a multi-beam optical trapping setup based on counterpropagating beam geometry. This system is capable of dynamic 3D positioning of particles with real-time user control. However, due to the serial nature of a modern mouse-driven user interface, a dynamic many-particle experiment can be difficult for the operator to handle. Here we present the trapping method and how to extend the capability of the user by using computer assisted trapping, and how the feedback for the computer can be enhanced. As a demonstration the system are used for controlling microfabricated tools and assemble custom made building blocks.

40 BF5 Optical biosensors using 2D bandgaps

By M. Kristensen 1 and

N. Skivesen 1 J. Canning 2 L.H. Frandsen 3

1 Department of Physics and Astronomy and iNANO, University of Aarhus, DK-8000 Arhus˚ C 2 School of Chemistry, University of Sydney, Sydney, Australia 3 Department of photonics engineering, DTU, DK-2800 Kgs. Lyngby A photonic band-gap is a frequency range where light cannot propagate in a micro-structured material. Concep- tually it is analogous to the well-known electronic band-gap from solid-state physics. We use line-defects in planar photonic band-gap silicon structures to confine light in waveguide-like geometries. Here the light propagates in a non- classical way, which allows us to enhance its sensitivity to spatially localized changes in refractive index. This is almost ideal for building a biosensor. We obtain high sensitivity by propagating light with frequencies in high-dispersion re- gions near cut-off of the fundamental waveguide defect-mode. In these frequency regions the group refractive index reaches values of more than 200. Further sensitivity enhancement is obtained by resonant effects due to point defects or polarization mixing leading to more than 100 times higher sensitivity. In addition, we obtain excellent selectivity since the light is spatially confined to regions within 50nm of the silicon- cladding interface. The light intensity there is extremely high since the continuity of the D-field implies a 6-12 fold increase in the E-field when passing from the silicon core to water or air cladding. We make the biosensors so the active sensor sites coincide exactly with these high-intensity regions for the light.

41 BF6 Design of Optical and Microfluidic modules for Single Cell Analysis

By Nimi Gopalakrishnan(*) and

K.Rau

National Centre for Biological Sciences, TIFR Bangalore, GKVK Campus, Bellary Road, Bangalore, India

(*) Present address: DTU Nanotech, Technical University of Denmark, DK-2800 Kongens Lyngby A microfluidic system is designed to analyze the activity of kinases in single cells with the aid of Electrophoresis and Fluorescence detection. Kinases phosphorylates the protein on which it acts. Thus the ratio of concentration of phosphorylated and dephosphorylated kinase peptides give the information of Kinase activity in a cell. For this, Channels of 50-20 µm are designed using negative Photolithography on silicon moulds. They are casted on with PDMS to make the microfluidic modules. Cells injected with a tagged reporter peptide to the kinase protein, is allowed to flow through these channels( 50-20 µm) using hydrodynamic flow. Electrodes across the channels provide the field for the contents, bursted out∼ by a nano second laser, to seperate providing a mass by charge ratio. An Optical Module, designed under the epiluminescent principles, detect the fluorescent contents downstream the channel. The Detector in the setup, connected to a computer through Lock-in Amplifier, calculates the fluorescence in each seperated content(10pM). An analysis on 10-15 cells can give a better data compared to the population studies in cells.

42 BF7 Chiral Vibrational Spectroscopy on the Single Molecule Level

By Salim Abdali 1 and

Christian Johannessen 1,2 Peter White 3

1. Quantum Protein Centre, QuP, Dept. of Physics, DTU 2. Dept. of Chemistry, University of Glasgow, UK 3. Dept. of Forensic and Biomedical Sciences, Lincoln University, UK Chiral Raman spectroscopy, widely known as Raman Optical Activity (ROA), is a vibrational tool, which besides information on structure and folding of molecules, it provides information on their chirality. However, it requires fully control of the polarisation of the light, simultaneously in the right- and left circular polarisation, and highly sensitive detection. Consequently and because that the signal collection involves subtraction of the left and right scattered light, the ROA signal is much weaker than the Raman, and therefore higher concentration and longer acquisition time have been normal conditions for ROA. After the discovery of the Surface Enhanced Raman effect, or SERS in 1974, combining SERS with ROA (into SEROA) was a natural step to be taken, in that the giant signal (up to 1014) provided by SERS was thought to enable much faster ROA measurements and for much lower concentration, even down to the single molecule level. Nevertheless, it should pass three decades before reliable SEROA studies have been achieved, and in spite of the fact that these studies are not yet on the single molecule level, they do provide SEROA from very low concentration (µM-nM). The technique and results from Enkephalin, myoglobin and cytochrome c will be presented.

43 BF8 Volume and energy fluctuations as a function of time of simulated phospholipid membranes

By Ulf R. Pedersen 1, and

G¨unther H. Peters 2, Thomas B. Schrøder1, Jeppe C. Dyre 1

1 DNFR center “Glass and time”, Department of Science, Systems and Models, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark

2 Center for Membrane Biophysics (MEMPHYS), Department of Chemistry, Technical University of Denmark, DK-2800 Lyn- gby, Denmark In general, many parameters are needed to describe microstates of a system. A phospholipid membrane is com- plex system and there is no obvious reason why fluctuations of say energy and volume should be correlated in time. Nevertheless, it have been suggested that close to the Lα Lθ phase transition they are [PNAS 102, 9790 (2005)]. This is indirectly supported by experiments [J. Phys. Chem.→ B 105, 7353 (2001)].

Similarly, it has recently been conjectured that a class of simple liquids exhibits strong correlations, including van der Waals bonded liquids but not hydrogen bonded liquids [Phys. Rev. Lett. 100, 015701 (2008)]. Phospholipid membranes contain van der Waals bonds as well as hydrogen bonds, thus the connection to simple liquids is not obvious.

We present data from simulations of a range of all-atom fully-hydrated membranes in the fluid Lα as well as in the gel Lθ phase. We demonstrate that slow fluctuations (nanoseconds) exhibit strong correlations between volume and energy [AIP Conf. Proc. 982, 407 (2008);arXiv.com, 0709.2781] and investigate the conjecture that slow fluctuations are dominated by the van der Waals bonded core of the membranes.

44 BF1P Stiffness of the cellular cytoskeleton.

By Anders Rosengren 1, and

Istvan Horvath 1,2, Judit Ovadi2, Kirstine Berg-So rensen3, Lene Oddershede1

1Niels Bohr Institute, University of Copenhagen 2Institute of Enzymology, Hungarian Academy of Science 3Department of Physics, Technical University of Denmark One of the central players of a cells skeleton is the hollow cylinders of polymerized tubulin, known as the micro- tubules. Motorproteins use microtubules as highways for intracellular transport, and during cell division microtubules are responsible for the separation of replicated chromosomes. Microtubules also influence the shape and for some cells take part in cell movement. Especially the first two properties makes microtubules interesting regarding cancer and possible neurological diseases. The physical properties of microtubules can and have been quantified measuring their persistence length, but with previous estimated values spanning a wide range. By fixation of one end of a microtubule and attachment of a bead along or at the free end, the persistence length of microtubules can determined by monitoring the bead’s thermal fluctuations. These thermal fluctuations are measured by an optical trap. ewline A series of experiments estimating the persistence lengths dependency of total microtubule length will be carried out. The measurements are to be done on non-physiological Taxol stabilized microtubules, and on microtubules ’stabilized’ by the protein Tppp/p25 mainly associated with neurological cells. Taxol, when present in appropriate volume, prevents the depolymerization of tubulin and thereby eliminates the dynamic nature of microtubules. This stabilizing effect of Taxol is currently applied in treatment of cancer, as it prohibits successful celldivision. It is currently unclear how Tppp/p25 stabilize microtubules.

Hopefully these experiments will give further insight in the architecture and nature of microtubules, and specifically on the role of Tppp/p25.

45 BF2P Fullerenes May Induce Toxic Physical Changes of DNA

By Fabian Czerwinski 1, and

Michael A. Sørensen 2 Lene B. Oddershede 1

1 Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark, 2 Department of Molecular Biology, University of Copenhagen, Ole Maaløesvej 5, 2200 Copenhagen, Denmark

Fullerenes are fascinating symmetric carbon nanostructures. Nowadays, they are widely used because of their char- acteristic physical and chemical properties. Until now re-search has been mainly focused on commercial applications of fullerenes. Only a few investigations have addressed the potential biological hazards, one of which is that ful-lerenes are believed to alter the elastic properties of DNA upon binding.

In our experiments we use optical tweezers with sub-piconewton and nanometer resolu-tion to probe the structural changes and the potential damages which fullerenes might induce on single DNA molecules. Therefore, force-extension relations can be obtained under physiological conditions while varying the concentration of different types of fullerenes.

It has theoretically been predicted [1], that certain fullerenes can function as a minor-groove binder to double-stranded DNA, thus altering its elastic properties significantly. Fullerenes are capable of causing severe damage inside living organisms by forming DNA regions which are not accessible for proper enzymatic functions. A further goal of the study is to establish fullerenes as a tool for a more detailed investigation of DNA-protein interactions, such as the trafficing of polymerases or the packing by prokaryotic proteins.

[1] Zhao, Striolo, and Cummings: BiophysJ (89):3856-62, 2005.

46 BF3P Polymeric substrates for FISH analysis

By Indumathi Vedarethinam1 and

Jacob M. Lange1,Maria I. Dimaki1, Casper .Clausen1,Pranjul J. Shah1,Winnie Svendsen1,Zeynep T¨umer2and Niels Tommerup2

1. DTU Nanotech – Department of Micro- and Nanotechnology, Technical University of Denmark, Bldg. 345E, 2800 Kgs. Lyngby, Denmark 2. Wilhelm Johannsen Centre for Functional Genome Research, Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Bldg. 24.4, Blegdamsvej 3, 2200 København N., Denmark

FISH (Fluorescence In Situ Hybridisation) is a widely used diagnostic tool for the detection chromosomal rearrange- ments in genomic DNA. Accurate clinical diagnosis of various genetic disorders could be achieved by ideally replacing the conventional methods which is easy to use, fast and cost-effective methods using plastic material. To this end, our present study investigates the substrate compatibility of different polymers polymers [poly methyl methacrylate (PMMA), polycarbonate, cyclic olefin copolymer (COC), and PDMS (polydimethylsiloxane)] to develop a Lab-on- Chip for FISH analysis. We used slide sized substrates with all the above mentioned polymers to perform FISH using immobilised cells and random probes. Our results showed that COC and PDMS were optimal surfaces for performing Lab-on-Chip FISH because of their non auto-fluorescence property. Further more, though PDMS has excellent optical property, we could not immobilise the cells on this surface because of its unique surface property. However, this was overcome by making and testing PDMS rough surfaces, which gave good results. Also, PC could not be used for this study because of its high auto-fluorescence. Finally our results were consistent with a previous study[1] which shows PDMS to be a surface of choice for performing Lab-on-Chip FISH analysis.

47 BF4P Improved measurement of the motion of a single protein, Lambda receptor, in the bacterial outer membrane

By Lei Xu1 and

Tabita Winther Madsen1, Kirstine Berg-Sørensen2, Lene B. Oddershede 1

1Niels Bohr Institute, University of Copenhagen, 2Department of Physics,Technical University of Denmark. Previously, we have studied the confined motion of a single protein, the lambda receptor, in the outer membrane of living Escherichia coli bacterium [1]. However, a delayed response due to the poor absorption of infrared light in the depletion zone of a silicon quadrant photodiode exerted a lowpass filtering of the high frequency part of the data [2]. To minimize this filtering, a position sensitive detector with an extended frequency response in the infrared region was used to measure the motion of the lambda receptor in the outer membrane of E. coli. We used the new setup to investigate the energy dependence of the mobility of the protein by blocking its metabolism pathway with membrane binding drugs. Reference 1. Oddershede et al., Biophys. J. 83, pp. 3152-3161 (2002). 2. Berg.Sørensen et al., J. Appl. Phys. 93, pp. 3167-3177 (2003).

48 BF5P Neurophysiology with three dimensional electrodes

By Patricia Vazquez and

Winnie Svendsen, Maria Dimakis, Jaime Castillo

DTU Nanotech, Denmark In the past, planar electrodes have been reasonably successful in recording the action potentials from cells in sus- pension, but the quality of the captured signal is poor, mainly due to the gap between the cells and the surface of the electrode. On top of that, the attachment and survival of the cells for a long term span is still an issue to tackle.

Several reports had shown the benefit of using three dimensional electrodes to record and stimulate electrical ac- tivity in neuron cells [1-3]. Encouragingly, cells seem to find a better affinity to these micro-pillars, since it mimics more closely the in-vivo environment than planar structures [3]. The 3D electrodes will detect larger signals than conventional planar electrodes since they’ll be close to the source of the signal. Moreover, due to their larger surface areas they will offer a better signal-to-noise ratio (recording) and higher safe-charge injection limit for electrical stimulation [1]. In this work, standard lithography methods are used to create the electrode structures in a microfluidic chamber.

References:

[1] Heuschkel, M.O., et al., A three-dimensional multi-electrode array for multi-site stimulation and recording in acute brain slices. Journal of Neuroscience Methods, 2002. 1142: p. 135-148. [2] Thiebaud, P., et al., Microelectrode arrays for electrophysiological monitoring of hippocampal organotypic slice cultures. IEEE Transactions on Biomedical Engineering, 1997. 44(11): p. 1159-1163. [3] Rajaraman, S., et al., Microfabrication technologies for a coupled three-dimensional microelectrode, microfluidic array. Journal of Micromechanics and Microengineering, 2007. 171: p. 163-171.

49 BF6P Characterization of liquids in commercial plastic and glass bottles with THz reflection spectroscopy

By Uffe Møller 1, and

Jens Kristian Jensen 1, Jacob Riis Folkenberg 2, Peter Uhd Jepsen 1

1 DTU Fotonik – Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark,

2 FOSS Analytical A/S, Slangerupgade 69, DK-3400 Hillerød, Denmark We demonstrate a method based on self-referenced THz time-domain spectroscopy for inspection of liquids in commercial plastic and glass bottles. We demonstrate that it is possible to determine the alcohol content of a liquid, and that liquids can be classified as either harmless or inflammable. The method operates in reflection mode with the result that liquids opaque to THz radiation can be characterized with little influence of the bottle shape. The method works with plastic bottles as well as glass bottles, with absorption of THz radiation by the plastic or the glass being the limiting factor. The reflection mode allows for automatic control of the validity of the measurement. The method will be useful in liquid scanning systems at security checkpoints.

50 BF7P Cold plasma source for bacterial inactivation at atmospheric pressure

By Weifeng Chen 1, and

Eugen Stamate 1, Ole Mejlholm 2, Paw Dalgaard 2

1Plasma and Technology Programme, Risø National Laboratory for Sustainable Energy, Technical University of Denmark 2 Department of Seafood Research National Institute for Aquatic Resources, DTU-Aqua, Technical University of Denmark A dielectric-barrier discharge system for cold plasma production was built for bacterial inactivation purpose. The effect of cold plasma treatment on sensory properties of seafood products was studied to establish how the sensory properties (e.g. appearance, texture) of seafood were affected by different plasma treatment conditions (e.g. power, frequency, time). Preliminary experiments were also performed to evaluate the effect of plasma treatment time on the reduction of the concentration of microorganisms (Lactobacillus sakei and Photobacterium phosphoreum) on inoculated slides of Long & Hammer agar. The results show that the concentration of Lb. sakei on agar slides was reduced significantly (P ¡ 0.05) on samples treated with cold plasma for 120 seconds. Treatment of agar slides with cold plasma for 60 seconds was sufficient to reduce the concentration of P. phosphoreum to below the detection limit, corresponding to a reduction of ¿ 4-5 log (cfu/g). Further studies are need on the effect of cold plasma treatments on sensory properties of cold-smoked salmon.

51 Condensed matter physics

FF1 Broadband shear mechanical and dielectric investigation of monohydroxy alcohols close to the glass transition temperature

By Bo Jakobsen and

Claudio Maggi Tage Christensen Jeppe C. Dyre

DNRF centre “Glass and Time”, IMFUFA, Department of Sciences, Roskilde University, Denmark.

Liquids close to the glass transition temperature generally show two relaxation processes which can be observed by dielectric and shear mechanical relaxation spectroscopy (e.g. [1]): the main structural (alpha) relaxation, and the (Johari-Goldstein) beta relaxation.

In monohydroxy alcohols an additional low frequency relaxation process (alpha-prime) is known to be observed by dielectric spectroscopy. The dielectric relaxation strength of this alpha-prime process is around 100 times larger than that of the alpha relaxation and it is Debye.

In this work we present broadband (1mHz-50kHz) shear mechanical measurements on monohydroxy systems, along with complementary dielectric data. The shear mechnical data are obtained using the piezoelectric shear modulus gauge (PSG) [2].

Data on the spectral shapes and relaxation times are compared between the two techniques. Shear mechanical spectroscopy allows for a clear identification of the structural relaxation process of the liquid, and its signature in the dielectric spectrum.

[1] B. Jakobsen, K. Niss, and N. B. Olsen, extitJ. Chem. Phys., extbf123, 234511, 2005.

[2] T. Christensen and N. B. Olsen, extitRev. Sci. Instrum., extbf66, 5019, 1995.

52 FF2 Quantum transport through quantum dots: effects of superconducting leads

By Brian M. Andersen and

Jens Paaske Karsten Flensberg

Niels Bohr Institute, University of Copenhagen Recent experiments of carbon nanotubes and nano-wires have revealed interesting features at low energy when the contacting leads become superconducting. This happens in the regime of weak coupling to the leads where Coulomb blockade is important. I discuss various ways to model this situation theoretically using non-equilibrium Green functions techniques and rate equations. Several interesting features resulting from asymmetric coupling will be discussed in detail.

53 FF3 Connectivity and Entanglement Stress Contributions in Strained Polymer Networks

By C. Svaneborg 1, and

Ralf Everaers 2, Gary S. Grest 3, John G. Curro 4

1 Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), University of Aarhus, Langelandsgade 140, DK-8000 305rhus, Denmark. 2 Universit´ede Lyon, Laboratoire de Physique, Ecole´ Normale Sup´erieure de Lyon, CNRS UMR 5672, 46 all´ed’Italie, 69364 Lyon Cedex 07, France 3 Sandia National Laboratories, Albuquerque, New Mexico 87185 4 Department of Chemical & Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico 87131

Using molecular dynamics simulations and a variant of our primitive path analysis algorithm, we have measured the total stress as well as the connectivity stress contribution for a large variety of generic bead-spring model polymer networks. For randomly cross- and end-linked networks the infered entanglement stress contribution is excellent agreement with the predictions of the slip-tube model [M. Rubinstein and S. Panyukov, Macromolecules 35, 6670 (2002)]. For networks undergoing further cross-linking and bond-breaking in the strained state (chemical aging), the observed stress-strain behavior can be described by a generalization of the slip-tube model in the spirit of Tobolsky’s independent network hypothesis. The stress-transfer between independent networks during post-curing appears to obey unexpectedly simple relations.

54 FF4 Singlet-Triplet Physics and Shell Filling in Carbon Nanotube Double Quantum Dots

By Henrik Ingerslev Jørgensen and

Kasper Grove-Rasmussen Karsten Flensberg Poul Erik Lindelof

Nano-Science Center, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100∼Copenhagen Ø , Den- mark An artificial two-atomic molecule, also called a double quantum dot (DQD), is an ideal system for exploring few electron physics. Interactions between just two electrons have been explored in such systems utilizing the singlet and triplet states as the two states in a quantum two-level system. An alternative and attractive material for studying spin based two-level systems is the carbon nanotube (CNT), because it is expected to have a very long spin coherence time. Here we show that the CNT DQD has a clear shell structure of either four or eight electrons. We show that few electron physics can be explored in these shells and we find that the singlet and triplet states are present in the four-electron shells. We furthermore observe inelastic cotunneling via the singlet and triplet states, which we use to probe the splitting between singlet and triplet, in good agreement with theory.

55 FF5 Structural Dynamics in Organic Semiconductors

By Henrik Till Lemke 1, and

Tine Ejdrup 1, Dag Werner Breiby 2, Peter Hammershøj 1, Yanhong Tong 1, Niels Harrit 1, Robert Feidenhans’l 1, Martin Meedom Nielsen 1

1 Centre for Molecular Movies, Niels Bohr Institute, University of Copenhagen 2 University of Trondheim

The structural environment in organic semiconductors during and after an electronic excitation changes the condi- tions for the charge carriers. The knowledge of transient structures is therefore essential for a complete understanding of processes like charge separation and charge transport. These processes are exploited in functional materials for large scale technical applications and are therefore of a high technological and scientific interest. We have investigated thin, polycrystalline films of perylene by time resolved X-ray diffraction. The 200-800 nm thick vapour deposited films were investigated by the optical pump – X-ray probe method which delivered structural infor- mation at 100 ps time resolution. The transient diffraction signal shows an thermal expansion of the crystal lattice which decays by the heat exchange with the substrate. Overlaid to this expansion we observed lattice vibrations in the MHz to GHz regime. Their oscillatory behaviour can be explained by standing modes of coherent phonons in transversal direction to the laser induced heat gradient. They can be excited due to the anisotropic thermal expansion coefficients of the film material. The observed propagation can be described by the elastic constants of the crystal material and the boundaries of the thin film.

56 FF6 Gate controlled tunnelling induced spin-reversal in a carbon nanotube Kondo dot with ferromagnetic contacts

By J.R. Hauptmann and

J. Paaske P.E. Lindelof

Niels Bohr Institute & Nano-Science Center University of Copenhagen In this talk I will describe carbon nanotubes (CNT), quantum-Kondo-dots and level renormalization before turning to the experiment. In the experiment we study CNT-quantum dots in the Kondo regime with ferromagnetic nickel contacts and we use the Kondo effect to probe the spin states. We see that the ferromagnetic electrodes induce a sizeable magnetic field called the exchange field in the CNT, splitting the normally degenerated spin states and thereby the Kondo peak, and that it is possible to compensate this splitting by applying an external field, thereby restoring the zero bias Kondo-peak. It is furthermore demonstrated that it is possible to control and reverse this tunnelling induced exchange fields and thereby the splitting of the spin states, merely by tuning the gate-voltage. This demonstrates a very direct electrical control over the spin-state of a quantum dot which, in contrast to an applied magnetic field, allows for rapid spin-reversal with a very localized addressing.

J.R. Hauptmann, J. Paaske & P.E. Lindelof. Nat. Phys.4, 373 (2008).

57 FF7 Investigations of the Antiferromagnetic Order Parameter in Nano-Sized YBCO Particles

By Jari ´ıHjøllum 1,2,3 and

K. Lefmann2, Ch. Niedermayer3, L. Theil Kuhn4, J. Raittila5, P. Paturi5, N. B. Christensen3, N. H. Andersen1, B. Lebech1

1 Materials Research Department, Risø DTU. 2 Niels Bohr Institute, Uni. of Copenhagen. 3 Paul Scherrer Institute, Villigen, Switzerland. 4 Fuel Cells and Solid State Chemistry Department, Risø DTU. 5 Physics Department, Uni. of Turku, Finland.

YBCO (YBa2Cu3O6+x) is maybe the best known high-temperature superconductor (HTSC), being the first su- perconductor with a TC above the boiling point of liquid N2. It is as the other cuprate HTSC antiferromagnetically ordered at low doping, and a superconductor at high doping. The superconductivity of YBCO is a two-dimensional phenomenon, existing even in materials only one unit cell high. However, it is well known that the dimensionality of the system affects the magnetic order in a material, with for instance a changed magnetization curve. We have manufactured disc-shaped YBCO with a diameter of 30nm and a height of 3nm, and using neutron diffraction (ND) and muon spin rotation (µSR) we have measured the staggered magnetization in the YBCO particles versus doping and temperature. The results show a significant lowering of both the N´eeltemperature and of the staggered magnetic order parameter compared to bulk. This shows that the magnetic order parameter in YBCO is a 3D phenomenon, in opposition to the superconducting order parameter. Furthermore the µSR results show the reentry of the magnetic order parameter at low temperature, previously only reported in bulk-sized systems. This observation strongly supports the view that the reentry is an intrinsic property of the cuprate systems.

58 FF8 Gate-dependent tunneling-induced level shifts observed in carbon nanotube quantum dots

By Jeppe V. Holm 1 and

Henrik I. Jørgensen 1, Kasper Grove-Rasmussen 1, Jens Paaske 1, Karsten Flensberg 1, Poul-Erik Lindelof 1

1 Niels Bohr Institute & Nano-Science Center, University of Copenhagen, Denmark

We have studied electron transport in clean single-walled carbon nanotube quantum dots. Because of the large number of Coulomb blockade diamonds simultaneously showing both shell structure and Kondo effect, we are able to perform a detailed analysis of tunneling renormalization effects. Thus determining the environment induced level shifts of this artificial atom. In shells where only one of the two orbitals is coupled strongly, we observe a marked asymmetric gate-dependence of the inelastic cotunneling lines together with a systematic gate dependence of the size (and shape) of the Coulomb diamonds. These effects are all given a simple explanation in terms of second-order perturbation theory in the tunnel coupling.

Phys. Rev. B. 77, 161406(R) (2008). http://link.aps.org/abstract/PRB/v77/e161406

59 FF9 New dynamical mode in magnetic nanoparticles

By Kim Lefmann 1,2 and

J. Garde 1, P. Hedeg˚ard 1, L. Theil Kuhn 2,3, S.N. Ancona 2, C.R.H. Bahl 2,3, C. Frandsen 4, S. Mørup 4

1 Niels Bohr Institute, KU 2 Materials Research Department, Risø-DTU 3 Department of Solid State Chemistry and Fuel Cells, Risø-DTU 4 Institute of Physics, DTU The magnetism of nanoparticles is essentially different from that of the corresponding bulk materials, both con- cerning structure and dynamics. The dominant type of excitations is an in-phase coherent precession (q=0) of all spins in the effective anisotropy field, known as collective magnetic excitations (CME). Another type is the flipping af the full particle moment, also known as superparamagnetism (SPM). The latter is important for applications in magnetic data storage, since it effectively causes the nanoparticle to loose its memory.

Using inelastic neutron scattering, the authors have over the last decade studied a number of features of the dy- namics of antiferromagnetic nanoparticles, and have e.g. directly observed CME and SPM. Although the theory was developed for ferromagnets, it seem to apply to antiferromagnets as well.

In this work we have studied the common mineral hematite (a-Fe2O3). For nanoparticles of d=8 nm, our observations were surprising. We expected a minor decrease of CME frequency with increasing temperature due to anharmonicities in the potential. In stead, we observed a 60% increase in frequency.

In order to resolve this apparent discrepancy, we performed classical numerical simulations of the spin dynamics in a nanoparticle. To simulate the heat bath, we used Langevin dynamics, which yields the temperature on an abso- lute scale.

The simulations reproduce the experimental data surprisingly well; in particular the increase in precession frequency. We find that, with increasing temperature, the angle between the two sublattice magnetisations deviate from 180 degrees. The resulting torque from the exchange interactions causes a fast rotation of both sublattices. We hence have discovered a new, exchange driven dynamic mode in antiferromagnetic nanoparticles.

60 FF10 Polarization effects in molecular junctions

By Kristen Kaasbjerg 1 and

Karsten Flensberg 1

1 Nano-Science Center, University of Copenhagen Understanding the electronic and chemical properties of molecules in nano-junctions is a key issue in the devel- opment of molecular electronics. Recent experiments on single organic molecules operating in the Coulomb blockade regime, have shown that the difference between the molecular ionization potential (IP) and the electron affinity (EA) is reduced by one order of magnitude compared to its gas phase value 1,2. It has been speculated that this reduction is caused by localization of the charges at the metallic leads 1. Indeed, polarization effects are known to alter the electronic properties of molecules 3,4,5, but a realistic and quantitative theoretical description of the surprisingly large effect in molecular junctions is still lacking. Here, we provide such a description by combining a semi-empirical descrip- tion of the molecule with a continuum description of the nanojunction and thus quantitatively explain the observed reduction. Moreover, the implication for the charge stability diagram is studied and we find alternating sizes of the Coulomb oscillations similar to the experimental findings. Our scheme is readily extended to more advanced quantum chemistry methods.

1 Kubatkin et al., Nature, vol. 425, p. 698 (2003) 2 Osorio et al., Adv. Mater., vol. 19, p. 281 (2007) 3 Neaton et al., Phys. Rev. Lett., vol. 97, p. 216405 (2006) 4 Repp et al., Phys. Rev. Lett., vol. 94, p. 026803 (2005) 5 Hesper et al., Europhysics Lett., vol. 40, p. 177 (1997)

61 FF11 Shear relaxation in viscous liquids

By Kristine Niss and

Bo Jakobsen, Claudio Maggi, Rasmus Godiksen, Tobias Larsen, Tage Christensen, Niels Boye Olsen, Jeppe Dyre

DNRF Centre “Glass and Time”, IMFUFA, Department of Sciences, Roskilde University, Denmark When liquids are cooled the eventually reach the melting point T m, where they freeze and form the crystal. How- ever at sufficiently high cooling rates most systems can be brought to supercool, meaning that the liquid is maintained below T m in a metastable equilibrium state. When the liquids are further cooled below T m their viscosity and characteristic relaxation time increases enormously. Temperature changes of just a few percent can lead to changes in the relaxation time and the viscosity, of several orders of magnitude. Cooling a liquid will ultimately make the relaxation time of the liquid surpasses the time scale of the cooling and the liquid consequently falls out of its (metastable) thermodynamical equilibrium. This phenomena is referred to as the glass transition and the non equilibrium “state” is referred to as a glass. The temperature dependence of the viscosity of most glass forming liquids is non-Arrhenius with an activation energy that increases significantly upon cooling. The most popular models explaining the temperature dependence of the activation energy are the (various) free volume models and the Adam-Gibbs entropy model. A less popular approach is advocated by the several closely related so-called elastic models, the main ideas of which date back to a paper by Eyring and co-workers from 1943. These models all one way or the other relate the activation energy to the liquid’s short-time elastic properties. The idea is that the relaxation is governed by an activated behavior and that the high frequency elastic moduli control the temperature dependence of the activation energy via a direct proportionality. [1] At Roskilde University we have developed a unique technique the Piezoelectric Shear-modulus Gauge method, that which can measure moduli in the GPa-range and it moreover covers an exceptionally large frequency range (1mHz-10kHz) [2]. It allows us to measure relaxation time and elastic modulus in one and the same measurement, and thereby gives a direct test of the elastic model. We have found quantitative agreement with the elastic model on a number of different molecular systems. [3]

[1] J.C.Dyre, Rev. Mod. Phys. 78, 953 (2006).

[2] T.Christensen, N.B.Olsen; Rev. Sci. Instr. 66, 5019 (1995).

[3] B.Jakobsen, K.Niss and N.B.Olsen; J. Chem. Phys, 123, 234511 (2005). J.C. Dyre, N.B.Olsen, T.Christensen; Phys. Rev. B 53, 2171 (1996). C.Maggi et al. in preparation. T.Larsen et al in preparation.

62 FF12 Ultrafast time-resolved X-ray investigations of molecules, liquids and solids

By Kristoffer Haldrup 1,2, and

Morten Christensen 1,3, Marco Cammarata 1,4, Niels Harrit 1,3, Martin M. Nielsen 1,2

1 Centre for Molecular Movies, University of Copenhagen, Denmark 2 Niels Bohr Institute, University of Copenhagen, Denmark 3 Department of Chemistry, University of Copenhagen, Denmark 4 European Synchrotron Radiation Facility, Grenoble, France By combining very short and intense laser pulses with the inherently time-structured radiation from synchrotron X-ray sources, structural evolution in chemical, physical and biological systems can now be directly followed on a time- scale well into the sub-nanosecond regime. Application of this technique to light-initiated chemical reactions in liquid solution has recently allowed us to directly determine key structural parameters for short-lived excited state complexes, exciplexes, a type of compounds known to play a significant role for the kinetics of many chemical reactions. -Other systems studied by the same methods currently include thin-film dynamics in organic semiconductors as well as solid- state phase transformations and formation of non-equilibrium melts in metals and semiconductors. This presentation will aim at demonstrating the general methodology for this type of experiments, illustrated through recent results obtained at the Centre for Molecular Movies, as well as provide an outlook towards the possibilities offered by a new generation of X-ray light sources – X-ray free electron lasers.

63 FF13 Optical trapping of single quantum dots for single molecule applications

By Liselotte Jauffred 1 and

Andrew C. Richardson 1 Lene B. Oddershede 1

1 Optical tweezer laboratory, The Niels Bohr Institute, University of Copenhagen. Colloidal quantum dots (QDs) are fluorescent semiconductor nanocrystals. They are bright and photostable with a broad excitation spectrum and a narrow emission spectrum, normally distributed around a specific wavelength, dependent on the size of the QD. The very low degree of photobleaching makes QDs suitable as markers or donors in single molecule assays. To investigate protein-DNA interaction through direct single molecule observations emphin vitro it can be advantageous to combine visualization with manipulation, or to measure the forces at play.

CdSe core QDs are experimentally proven to have a permanent dipole moment, this being an intrinsic property of the uncharged semiconducting nanocrystal. Furthermore, the dipole moment is shown to be proportional to the volume of the QD. It is known, that a dipole in the inhomogeneous field of the highly focussed trapping laser experi- ences a force in the direction of the field gradient. Therefore, a particle with an induced or permanent dipole moment will be forced towards laser focus by a three-dimensional restoring force. This allows for optical trapping of single colloidal QDs.

We have investigated the possibilities of using QDs as trapping handles. We have shown that individual CdSe core quantum dots can be optically trapped and manipulated in three dimensions. Moreover, we provide quantitative information about the spring constants involved, e.g. information about the magnitude of forces which can be applied on a single quantum dot and of the polarizability of these QDs.

64 FF14 Optofluidic tuning of polymer photonic crystal band edge lasers

By Mads Brøkner Christiansen and

Felipe Bernal Arango, Morten Gersborg-Hansen and Anders Kristensen

DTU nanotech Department of micro- and nanotechnology DTU building 345E 2800 Kgs. Lyngby We investigate two different effects of altering the cladding refractive index of symmetry modified polymer photonic crystal band edge lasers. The lasers are defined in a thin film of SU-8 photo-definable polymer, doped with the laser dye Pyrromethene 597. They are fabricated in parallel by combined nanoimprint and photolithography (CNP).

When optically pumped the lasers emit in the wavelength range from 550 nm to 650 nm, depending on lattice constant (a) of the photonic crystal lattice. Depending on which band edge the gain region of the dye overlaps, the lasers can emit vertically, at an arbitrary angle, or in the chip plane.

When fluid droplets of different refractive indices are positioned on the lasers the emission wavelength is altered. The maximal sensitivity is around 1 nm per 10-2 refractive index unit, making detection of 10-3 refractive index units relatively easy.

A device symmetry different from that of the photonic crystal is imposed by the global shape of the device. This causes the device to emit in fewer directions than expected, when considering the lattice alone. The relative intensities of the signals in different directions are shown to depend on cladding refractive index.

65 FF15 Coupling of Self-Assembled InAs Quantum Dots to Surface Plasmon Polaritons

By Mads Lykke Andersen 1 and

Søren Stobbe 1, Jeppe Johansen1 & Peter Lodahl1

1 DTU Fotonik, Technical University of Denmark The strong coupling offered by coupling quantum dots to surface plasmons has many applications including single- photon sources and single-photon transistors. To understand these phenomena, detailed knowledge of the coupling between a quantum dot and surface plasmons is needed. This knowledge can be acquired by placing well-characterized quantum dots in simple metallic structures with known plasmonic modes.

We have positioned self-assembled InAs quantum dots at different distances (between 0-300 nm) from a silver mirror. By measuring the decay rate of the quantum dots as a function of the distance to the silver mirror we can separate the different decay contributions of the quantum dot, whereby the coupling to surface plasmons can be extracted. We report that the measured quantum dot-plasmon coupling is weaker than expected from dipole theory, and propose that the deviation could be explained by a breakdown of the dipole approximation due to the extended size of the quantum dot.

66 FF16 Optofluidics for slow-light enhanced light-matter interactions

By Niels Asger Mortensen 1,2 1 Department of Photonics Engineering, Technical University of Denmark 2 Department of Micro and Nanotechnology, Technical University of Denmark

Optical techniques are finding widespread use in chemical and bio-chemical analysis. Consequently, there has dur- ing the past decade been an increasing emphasis on also integrating optics in miniaturized chemical analysis systems. Scaling analysis and experiments have demonstrated the advantage of microscale devices over their macroscopic coun- terparts for a number of chemical applications. However, from an optical point of view, miniaturized devices suffer dramatically from the reduced optical path compared to experiments performed in a macroscale environment, e.g. in a cuvette. Optofluidics may offer solutions to this by infiltrating strongly dispersive photonic structures with the liquid analyte of interest. In particular, we envision liquid-infiltrated photonic crystals as candidates for slow-light enhanced absorption measurements.

67 FF17 Pulse delay and advancement of ultrafast pulses in semiconductor waveguides.

By Per Lunnemann Hansen and

Mike van der Poel, Kresten Yvind, Jesper Mørk

DTU Fotonik, Technical University of Denmark Pulse delay and advancement of ultrafast pulses in semiconductor waveguides. Throughout the past decade, research on modifying the group velocity of light has received increasing attention. In order to understand and exploit the effects, a detailed understanding of light-matter interaction is necessary and is therefore of interest from a scientific point of view. Furthermore, effectively controlling the velocity of light is a key missing element for many applications such as buffering and routing in all-optical networks. Semiconductor material, as a slow light medium, is advantageous as it offers compactness suitable for photonic integration as well as the pos- sibility to custom design the light matter interaction by using well established growth and processing facilities. In this work, we present recent experimental work on gain and delay measurements of ultrafast pulses using semicon- ductor ridge waveguides. The achieved delay is based on a pulse shaping effect due to gain saturation that unfortunately comes at the cost of a significant attenuation of the signal. By cascading amplifying and absorbing waveguides and careful choice of applied electrical bias, this drawback can be avoided and is confirmed by our measurements. A model describing the pulse propagation is compared to our measurements and deviations from the predictions are discussed.

68 FF18 Superconducting tunneling through a carbon nanotube

By Poul Erik Lindelof 1 and

Henrik Ingerslev Jørgensen 1 Kasper Grove-Rasmussen 1 Karsten Flensberg 1 Tomas Novotny 1,2

1 Niels Bohr Institute and Nano-Science Center, University of Copenhagen 2 Department of Condensed Matter Physics, Charles University Prague, Czech Republic A single wall carbon nanotube placed between superconducting (Al, Nb) contacts act as a tuneable barrier [1]. This allows both Giaever and Josephson tunnelling to be observed through the few nm2 cross section and few hundred nm long barrier. The Josephson junctions at finite bias are dominated by multiple Andreev scattering. For high resis- tance contacts the tunnelling is dominated by single electron Coulomb blockade and can be periodically and strongly modulated by a gate voltage. For intermediate contact resistances ( h/2e2) interplay between the Kondo resonance (with an odd number of electrons on the single wall carbon nanotube)∼ and the Josephson effect is observed. In this 1 regime the Josephson current-phase relation is shifted by pi due to the tunnelling through a spin 2 state. Closer to the ideal contact ( h/4e2) the coulomb blockade is eliminated and the Josephson supercurrent gets closer to the ideal value 4Delta/eR, where∼ Delta is the superconducting energy gap of the electrodes. These nanoscale superconducting devices may allow new applications. [1] H.I. Jørgensen, K. Grove-Rasmussen, T. Novotny, K. Flensberg, P.E. Lindelof, Phys.Rev.Lett. 96, 207003 (2006); H.I. Jørgensen, T. Novotny, K. Grove-Rasmussen, K. Flensberg, P.E. Lindelof, Nano Letters 7, 2441 (2007); K. Grove- Rasmussen, H.I. Jørgensen, P.E. Lindelof, New Journal of Physics 9, 124 (2007).

69 FF19 Exciting Excitations in Magnetic Nanofoam

By Sonja Rosenlund 1 and

Adrian Hill 2 Niels Vesterg˚ardJensen 3 Kim Lefmann 1 Andrew Harrison 2,4

1 University of Copenhagen, Niels Bohr Instituttet, Denmark 2 The University of Edinburgh, Centre for Science at Extreme Conditions & School of Chemistry, UK 3 Risø-DTU, Dept. of Materials Research, Denmark 4 Institute Laue-Langevin, Grenoble, France

The large internal surface area of mesoporous solids of transition metal oxide provide a perfect arena for catalytic processes to take place and a huge effort has been put into synthesising these so-called nanofoams [1]. These unique samples open for the study of interesting fundamental questions related to the novel dimensionality of the system. Here we present the first study of magnetic dynamics in the antiferromagnetically ordered α-Fe2O3 (hematite) nanofoam.

With a pore-size of 2 – 15 nm and a wall thickness of less than 8 nm the sample is indeed nanosized, and the confined dimensionality of the nanofoam walls significantly changes the magnetic structure compared to both bulk hematite and hematite nanoparticles [2]. The nanofoam possesses the same long-range magnetic order as found in bulk hematite, yet the Morin transition observed in bulk hematite is suppressed due to size-effects as found in hematite nanoparticles [3].

To gain a better understanding of the magnetism of the nanofoam we have studied magnetic dynamics by means of inelastic neutron scattering. With the ability to monitor fast dynamics inelastic neutron scattering has proven an efficient method for the study of superparamagnetic relaxation and collective magnetic excitations in antiferromagnet- ically ordered nanosized structures [4]. We observe similar magnetic dynamics as seen in hematite nanoparticles [4, 5] but with additional long-range order and compare the results to dynamics observed in interacting 8 nm hematite nanoparticles [6].

70 FF20 Experimental demonstration of novel spatial quantum correlations induced by multiple scattering of light

By Stephan Smolka 1 and

Alexander Huck 2, Ulrik L. Andersen 2, Peter Lodahl 1

1 DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Building 345V, 2800 Kgs. Lyngby, Denmark

2 DTU Physics, Department of Physics, Technical University of Denmark, Building 309, 2800 Kgs. Lyngby, Denmark

We investigate the transport of non-classical light through multiple scattering random media. So far almost all experiments in the multidisciplinary field multiple light scattering have concentrated on the transport of light intensity. In recent years the quantum nature of multiple scattered light has been considered by studying the photon fluctuations of the light [1]. It was predicted that fluctuations below the classical limit can survive multiple scattering and novel spatial quantum correlations can be induced [2]. In accordance with the Heisenberg uncertainty principle, photon fluctuations smaller than the classical limit can only be generated with non-classical light sources. Using squeezed light we performed the first experimental demonstration that non-classical fluctuations survive multiple scattering of light. The experiments are in excellent agreement with theory. Moreover we demonstrate experimentally that multiple scattering induces novel spatial quantum correlations.

71 FF21 Coupling of Single Quantum Dots to a Photonic Crystal Waveguide

By T. Lund-Hansen 1, and

S. Stobbe, B. Julsgaard, H.T. Nielsen, P. Lodahl

DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark,

An efficient and high quality single-photon source is a key element in quantum information processing using pho- tons. As a consequence, much current research is focused on realizing all-solid-state nanophotonic single-photon sources. Single photons can be harvested with high efficiency if the emitter is coupled efficiently to a single enhanced mode. One popular approach has been to couple single quantum dots to a nanocavity, but a limiting factor in this configuration is that in order to apply the photon it should subsequently be coupled out of the cavity, reducing the overall efficiency significantly. An alternative approach is to couple the quantum dot directly to the propagating mode of a photonic waveguide.

We demonstrate the coupling of single quantum dots to a photonic crystal waveguide using time-resolved spontaneous emission measurements. A pronounced effect is seen in the decay rates of quantum dots coupled to the waveguide compared to uncoupled quantum dots. The frequency dependence of the coupling is compared to theoretical calcula- tions, and good agreement is found. From the measured decay rates we extract the efficiency of photon emission into the waveguide mode of between 50% and 90%, which demonstrates the high efficiency of the coupling.

72 FF22 Little evidence for dynamic divergences in ultraviscous molecular liquids

By Tina Hecksher 1 and

Albena I. Nielsen 2 Niels B. Olsen 3 Jeppe C. Dyre 4

(1-4) DNRF centre ”Glass and Time”, Roskilde University The physics of the ultraviscous liquid phase preceding glass formation continue to pose major unsolved problems. It is actively debated, for instance, whether the dramatic increase of the relaxation time reflects an underlying phase transition to a state of infinite relaxation time. To elucidate the empirical evidence for this intriguing scenario some of the most accurate relaxation time data available for any class of ultraviscous liquids – those obtained by dielectric relaxation experiments just above the glass transition – were compiled. Analysis of data for 42 liquids shows that there is no compelling evidence for the Vogel-Fulscher-Tamman (VFT) prediction that the relaxation time diverges at a finite temperature. We conclude that theories with a dynamic divergence of the VFT form lack direct experimental evidence.

73 FF23 Atomistic calculations of phonon transport in silicon nanowires

By Troels Markussen 1 and

Antti-Pekka Jauho 1,2 Mads Brandbyge 1

1 DTU Nanotech, Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 East, DK-2800 Kgs. Lyngby, Denmark 2 Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland We study theoretically the influence of vacancies on the thermal transport in silicon nanowires (SiNWs). An atomistic empirical potential model [1] is used together with a recursive Green’s function method [2] to calculate the phonon transmission through isolated vacancies as well as through long wires containing many vacancies. It is shown that, similar to the electronic conduction [3], the long wire transmission can be accurately estimated from the scattering properties of the isolated vacancies, and time consuming calculations can thus be avoided [4]. We find that wires oriented along the ¡110¿ direction have a higher thermal conductance and are less affected by vacancies than ¡100¿ and ¡111¿ wires. Bulk vacancies are found to scatter phonons more than surface vacancies, independently of wire orientation and diameter. Finally, the area normalized thermal conductance increases with decreasing diameter for pristine wires while it decreases for defective wires. These results could be important for future phonon-engineering of nanowire devices.

[1] J.D. Gale, JCS Faraday Trans., 93, 629, (1997) [2] T. Markussen et al. Phys. Rev. B, 74, 245313 (2006) [3] T. Markussen et al., Phys. Rev. Lett., 99, 076803, (2007) [4] T. Markussen et al. in preparation

74 FF1P Fabrication of Cantilevers by Nanoimprint Lithography

By A. Greve1 and

A. Greve, S. Keller1, D. Larson2, A. Kristensen1, K. Yvind2, J. Hvam2 and A. Boisen1

1 DTU Nanotech – Department of Micro and Nanotechnology, Technical University of Denmark, bldg. 345 east, Kgs. Lyngby, Denmark;

2 DTU Fotonik – Department of Photonics Engineering, Technical University of Denmark, Ørsteds Plads, DK 2800 Kgs Lyngby, Denmark;

This work presents the fabrication of micro cantilevers in a thermoplastic material by nanoimprint lithography (NIL). The cantilevers will later be used for bio/chemical analysis. A stamp is made in silicon and the stamp pattern is transferred to the thermoplast by NIL. The technique can transfer substructures on the cantilever and define the cantilever in one easy step. Cantilevers made by NIL have been realised in the thermoplast Topas. The cantilevers have a thickness of 5.5 µm, width of 100 µm and a length of 400 µm.

75 FF2P Generic properties of alpha relaxations in viscous liquids

By Albena Nielsen (a) and

Tage Christensen(a), Bo Jakobsen(a), Kristine Niss (a), Niels Boye Olsen(a), Ranko Richert (b) Jeppe C. Dyre(a)

(a): DNRF Centre “Glass and Time,” IMFUFA, Department of Sciences, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark

(b):Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, USA We present data for the dielectric relaxation of 53 glass-forming organic liquids, showing that the primary (alpha) relaxation is often close to square root of t – relaxation. The better an inverse power-law description of the high- frequency loss applies, the more accurately is the -1/2 power law relaxation obeyed.

These findings suggest that -1/2 power law relaxation is somehow generic to the alpha process, once a common view, but since long believed to be incorrect. Only liquids with very large dielectric losses deviate systematically from this picture. As a further challenge to the prevailing opinion, we find that liquids with accurate -1/2 power law relaxation cover a wide range of fragilities.

76 FF3P The world’s smallest mass-fabricated gripper

By Alberto Cagliani 1 and

Ozlem¨ Sardan 1 Karin Nordstr¨omDyvelkov 1 Dirch Hjort Petersen1 Berit Geilman Herstrøm 2 Peter Bøggild 1

1Department of Micro- and Nanotechnology DTU-Nanotech 2DTU-Danchip Previous microgrippers are able to manipulate structures down to 100 nm in diameter, whereas structures with dimensions in the 10-100 nm range have so far been inaccessible, eliminating a large number of potentially interesting nanowires, -tubes and heterostructures from being manipulated. We present here a new type of topology optimized polysilicon electrothermal nano-gripper, which address manipulation of structures in this size range. These nano-grippers are 10 folds shorter and 5 folds thinner than the previous micro- grippers, and gaps between the jaws down to 400 nm. The nano-grippers are 35 um to 50 um long and 1 um thick, and have been realized using a mix-and-match technique, where the actuator is defined with the E-beam lithography step and the electrical connections are realized by standard UV lithography. This combines the high throughput from photolithography, with the 10 nm resolution of electron beam lithography. For such small freestanding structures, the etching is very challenging. In order to obtain a well-controlled etch a two steps RIE process has been developed. We also demonstrate a novel approach to end-effector design, where a focused ion beam is used to define them. Finally, we show the first results of actuation and manipulation using the nanogrippers.

77 FF4P Kondo-model for a quantum dot with spin-orbit coupling

By Andreas Andersen and

Jens Paaske

Niels Bohr Institute, University of Copenhagen We study the influence of spin-orbit coupling on electron transport in quantum dot systems. We model the quantum dot by a parabolic confinement potential in which we retain only the two lowest lying eigenstates, which are subsequently coupled by a Rashba spin-orbit coupling in the dot. By means of a Schrieffer-Wolff transformation, this two-orbital Anderson model is mapped to a Kondo model, an effective low-energy description with spin, but no charge-fluctuations. In the presence of an external magnetic field, the spin-orbit coupling gives rise to a Kondo model with spin dependent exchange couplings with different quantization axis at source, and drain electrodes. We briefly discuss the possible experimental consequences for the cotunneling conductance and Kondo-effect in such quantum dot systems.

78 FF5P Lab-On-A-Chip microsphere based suspension array based on pinched flow fractionation

By Asger Vig Larsen [1] and

Lena Poulsen[1] June H. Rasmussen[1] Peter B. Muller[1] Henrik Birgens[2] Martin Dufva[1] Anders Kristensen[1]

[1]: Department of Micro and Nanotechnology, Technical University of Denmark

[2]: Department of Haematology, Herlev Hospital, University of Copenhagen We demonstrate a lab-on-a-chip microsphere based suspension array, where pinched flow fractionation (PFF) [1] is used to separate different sized beads and each element of the array is formed by one bead size. Multiplex analysis of clinical samples is accomplished when each array element – or bead size – bears different surface receptors. Read-out is based on fluorescence detection. In order to simplify operation, the PFF microfluidic chip is designed so suction at the outlet is sufficient to drive the separation and thereby enable analysis. The method is demonstrated by analysis of human DNA associated with the blood disorder beta thalassemia from three beta thalassemia patients, two homozy- gotes and one heterozygote. The analysis takes approximately 10 minutes, from introducing prepared beads into the chip until the result is ready [2]. The devices were fabricated in polymer using single step nanoimprint lithography. The micro channels are 13 µm high, and range from 11.7 µm to 400 µm in width, enabling separation of particles smaller than 11.7 µm. The devices are designed so that the ratio of the hydraulic resistance in the two inlet channels enables pinching of beads introduced from the bead inlet, when suction is added at the outlet. The PFF microfluidic chip was tested to separate fluorescently labelled polystyrene beads with six different bead sizes: 1 µm, 1.59 µm, 2.1 µm, 2.5 µm, 3 µm and 4 µm. The position of the different bead sizes after separation was determined optically in the broadening segment.

References: [1] M. Yamada et al., Anal. Chem. 76, pp. 5465-5471 (2004). [2] A. V. Larsen et al, Lab Chip, in press (2008)

79 FF6P Magnetic refrigeration at room temperature – cooling stuff using magnets

By Britt Rosendahl Hansen and

Luise Theil Kuhn

Risø National Laboratory for Sustainable Energy, Technical University of Denmark (DTU) In the industrialized world most of us enjoy the benefits of being able to store e.g. food or medicine for extended periods, air-conditioning of homes and vehicles, and the products of industries which require refrigeration during the manufacturing process. Indeed the advantages of refrigeration cannot be overestimated.

Today refrigeration in industry and homes is primarily achieved by the vapor-compression cycling of a gas. The gasses used in such refrigeration have often changed with time as they were either known to be toxic, e.g. ammonia, or later found to be harmful in some way to the atmosphere, e.g. CFCs.

Our group at Risø DTU investigates magnetic refrigeration as an energy efficient alternative for refrigeration at room temperature. Here, a magnetic field is applied and removed in a cycle that causes a magnetic material to alternately heat up and cool down. This is known as the magnetocaloric effect and on our poster you can learn just why it occurs and how it can be used to cool stuff. The poster will introduce the magnetic refrigeration process in a way that everyone will understand and it will also delve into physics with a focus on the required properties of the magnetic material.

80 FF7P AFM Mechanical Measurements on Nanowires in 3D

By C. Kallesøe 1 and

M. Larsen 1 K. Mølhave 1 P. Bøggild 1

1 DTU Nanotech – Department of Micro- and Nanotechnology, NanoDTU, Technical University of Denmark

Nanowires are rod-like structures with diameters of tens up to a few hundred nanometers, which can be grown epitaxially from substrates. Due to their small size, they can show peculiar mechanical and electrical properties, and examining the consequences for the mechanical properties are therefore of great importance. Such investigations could involve Youngs Modulus for narrow structures, the influence of heterostructures in the nanowires, the strength of the interface to the substrate is for a lattice mismatched epitaxial nanowire grown on silicon, as well as the piezoelectric behaviour.

In this work a simple method to characterize the mechanical properties of a three dimensional nanostructure, such as a nanowire standing out from a planar substrate, has been developed. With an Atomic Force Microscope, AFM, the cantilever probe is used to deflect a horizontally aligned nanowire repeatedly at different positions along the nanowire, which enables accurate determination of the spring constant. From these measurements the product of Moment of inertia and Young’s modulus can be found on many individual nanowires in short time. Based on this method Young’s Modulus of “nanorods”, such as carbon nanotubes and epitaxial grown III-V nanowires, has been determined.

81 FF8P Supercooled liquids dyamics studied in shear-mechanical spectroscopy

By C. Maggi 1 and

B. Jacobsen 1, T. Christensen 1, N. B. Olsen 1 and J. C. Dyre1

1 Roskilde University Center The study of the slow dynamics in supercooled liquids is one of the central topics in glass-physics. Experimentally the tool that is mainly used to analyze the relaxation processes associated with this dynamics is dielectric spectroscopy. However other response functions could be potentially very interesting to measure. It is not well understood, in fact, if the various observables display some universal features approaching the glass transition and how they are related to each other. Furthermore the mechanical properties of these ultra-viscous liquids are deeply interesting from a pratical and theoretical point of view.

These motivations lead us to exploit a recently-developed experimental technique to access the frequency-resolved shear modulus of several glass-forming liquids. We report dynamical shear modulus measurements for five glass- forming liquids (silicon oil, diethyl phthalate, dibutyl phthalate, 1,2-Propanediol, 1,3-Propanediol). The shear me- chanical spectra are obtained by the piezoelectric shear modulus gauge (PSG) method [1]. This technique allows us to measure the shear moduls (100 kPa – 10 GPa) of the supercooled liquid close to the glass transition temperature within a wide frequency range: 1 mHz – 50 kHz.

We analyze the frequency-dependent response functions checking if time temperature superposition (TTS) is obeyed. We also study the shear loss peak position and its high-frequency part. It has been suggested indeed that, when TTS applies, the high frequency side of the imaginary part of the dielectric response decreases like power law of the frequency with an exponent equal to -1/2 [2]. This is also supported by a recent theoretical work [3]. This conjecture is analyzed on the basis of the shear mechanical data. A model for viscous liquids dynamics that relates the shear modulus and the alpha relaxation time has been proposed [4]. A test of this model is made possible by these mechan- ical measurements so its prediction is compared with the experimental data.

[1] T. Christensen and N. B. Olsen, Rev. Sci. Instrum. 66, 5019 (1995). [2] N. B. Olsen, T. Christensen, and J. C. Dyre, Phys. Rev. Lett. 86, 1271 (2001) [3] J. C. Dyre, Europhys. Lett. 71, 646 (2005). [4] J. C. Dyre, N. B. Olsen, and T. Christensen, Phys. Rev. B 53, 2171 (1996)

82 FF9P High precision micro-scale Hall Effect characterization method

By D.H. Petersen 1,2, and

O. Hansen 1,3, T. Clarysse 4, J. Goossens 4, E. Rosseel 4, W. Vandervorst 4,5, R. Lin 2, P.F. Nielsen 2

1 DTU Nanotech – Dept. of Micro and Nanotechnology, Technical University of Denmark, building 345 East, DK-2800 Kgs. Lyngby, Denmark, 2 CAPRES A/S, Scion-DTU, building 373, DK-2800 Kgs. Lyngby, Denmark , 3 CINF – Centre for Individual Nanoparticle Functionality, Technical University of Denmark, building 345 East, DK-2800 Kgs. Lyngby, Denmark, 4 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium, 5 KU Leuven, Department of Physics-IKS, Celestijnenlaan 200D, B-3001 Leuven, Belgium

We report a new Hall Effect measurement method for characterization of semiconductor thin-films without the need for conventional Hall Effect geometries and metal contact pads. The method differs from conventional van der Pauw measurements since the four probe pins (contacts) are placed in the interior of the sample region, not just on the perimeter. We find the analytical expressions for the measured four-point resistance in presence of a magnetic field and for several simple sample geometries. We show how the sheet resistance and Hall Effect contributions may be separated using dual configuration measurements. We then experimentally verify the method by micro four-point probe measurements on several different ultra-shallow junctions (USJ) in silicon and germanium. On a cleaved silicon wafer with an ultra-shallow junction we determine carrier mobility, sheet carrier density, and sheet resistance from micro four-point probe measurements under various experimental conditions, and show with these conditions reproducibility within less than 1.5%. Finally, we demonstrate the high spatial resolution of the new method by characterization of sub-melt laser annealed USJ, with non-uniform dopant activation and a measurement repeatability ¡1%.

83 FF10P Surface acoustic wave modulation of planar photonic circuits

By Elaine Cristina Saraiva Barretto 1 and

Mike van der Poel 1

1 DTU Fotonik – Department of Photonics Engineering, Technical University of Denmark. In this project, we study the use of acousto-optical effects in Mach-Zehnder interferometers (MZI), by means of surface acoustic wave (SAW) modulation of the waveguides. The SAW field is excited by applying an electrical RF field to an interdigital transducer (IDT) on a piezoelectric material (like GaAs or ZnO). The SAW strain field results in a periodic refractive index modulation of the material, that leads to the optical phase change between the arms of the MZI. Advanced mechanisms to enhance the interaction between the SAW field and the waveguides – and then increase the modulation depth – will also be studied, for instance using photonic crystals in the arms of the MZI. Among the types of components to be explored in this project are frequency and phase shifters and intensity modu- lators.

84 FF11P Vacuum-driven Pinched Flow Fractionation

By Eric Jensen 1 and

Asger V. Larsen 1 Anders Kristensen 1

1 DTU Nanotech, Technical University of Denmark, Kongens Lyngby

PFF is a field fractionation separation technique which relies on laminar flow of a liquid in a device with a specific geometry in order to separates solid particles by size. A PFF device has two inlets which meet in a y-section. The flow in the buffer inlet is higher than the flow in the bead inlet, thus pinching the latter to the sidewall of the third channel from the y-section. This channel opens up into a wider tunnel and the beads are separated due to a spreading of streamlines.

A PFF device is driven by two pumps which determine the flow in the two inlet channels. The new device, VdPFF, uses vacuum instead of pressure to drive the flows. For this to be achieved a new device design was developed. The inlet channels are designed to have a specific hydraulic resistance such that the flow ratio is sufficient to pinch beads with a diameter smaller than 1 µm.

We demonstrate analytical separation of 5 different sized beads.

85 FF12P Purcell enhanced coupling of quantum dot emission to photonic crystal nano-cavities

By H. Thyrrestrup 1 and

T. Lund-Hansen 1 P. Lodahl 1

1 DTU Fotonik, Technical University of Denmark We present measurements of the coupling of light emitted from InAs quantum dots to photonic crystal nano-cavities. The cavity consists of a lattice defect in a 2D photonic crystal membrane. Such a defect strongly confines light to a localised mode in the photonic crystal and thereby increases the density of optical states inside the cavity region. This is identified by strong enhancement in the quantum dot emission spectra and a decreased exciton recombination lifetime for quantum dots that spectrally and spatial overlap with the cavity mode. Using single photon correlation measurements we have successfully measured a decreased lifetime for quantum dots coupled to a nano-cavity and identified cavity resonances that match well with numerical simulations.

86 FF13P Novel electrode fabrication method for organic nanofiber light emitting devices

By Henrik H. Henrichsen Department of Micro- and Nanotechnology, Technical University of Denmark The most common way to fabricate organic light emitting devices (OLEDs) is to apply the organic layer and electrode materials in a sandwich-like structure. In this way thin film devices can be constructed routinely in ad- vanced multilayer structures. Organic nanofibres are candidates for future nano-photonic structures, which however cannot be fabricated using conventional techniques. This work proposes a simple method for interfacing parallel para- hexaphenylene nanowires grown on an insulating mica surface. The cathode electrode is made by e-beam deposition of Al through a mechanical shadow mask, creating a rectangular stripe on the substrate, which is oriented perpendicular to the nanowires. An insulating layer is created by oxidation of Al or deposition of an oxide, and finally tin-doped indium oxide (ITO) is deposted as anode. The advantage of the method is the simple approach to realising nano size electrode gaps and that the organic structures are encapsulated thus protected from the ambient atmosphere.

87 FF14P Neutron guide optimization

By Kaspar Hewitt Klenø1 and

Kim Lefmann1 Peter Willendrup2 Erik Knudsen2 Peter Boni3

1 Niels Bohr Institute, University of Copenhagen 2 RisøNational Laboratory 3 Technical University of Munich A neutron guide is the essential komponent of a neutron instrument, which directs the neutron beam from the source to the target sample. Most neutron guides today use simple 12x3 cm regtangular guides, with uniform ’supermirror’ coating. This project explores alternative guide shapes and coating distributions, specifically 100 m and 300 m long guides, for use at the European Spallation source. We investigate both tapering, ballistic and elliptical guides, and demonstrate that proper shaping and coating distri- bution leads to dramatic improvements in guide efficiency, both in terms of absolute intensity and cost efficiency.

88 FF15P Mitochondrion optimization using thermodynamic geometry

By Kristian Bødker Frederiksen and

Bjarne Andresen

Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø , Denmark The general theory of thermodynamic geometry [1] allows us to analyze a general thermodynamic state space in the mathematical framework of metric spaces. With these mathematical tools, the Horse-Carrot theorem for thermody- namic step processes was developed [2], and allows us to calculate an explicit lower bound for the entropy production, and corresponding optimal states, of such a step process. This has previously been applied to the case of optimizing a fractional distillation [3]. The poster will introduce a purely chemical example of such a step process optimization, based on the Electron Transport Chain (ETC) in the mitochondria.

The chain consists of three basic protein catalyzed reactions, which may be analyzed using the electrochemical potential as a generalized reaction coordinate. We derive the metric structure on the corresponding thermodynamic state space and calculate the optimal electrochemical distribution of the mobile electron carriers ubiquinone and cytochrome-c. Good agreement is found between the calculated optimal configuration and consensus values in observed mitochondria under standard physiological conditions. Using the developed metric, the behavior of the ETC under variable external conditions like changing pH and changes in oxygen concentration is considered.

[1] Weinhold. The Journal of Chemical Physics (1975) vol. 63 6 pp. 2479-2483 [2] Salamon et al. Physical Review Letters (1983) vol. 51 pp. 1127-1130 [3] B. Andresen, P. Salamon: Optimal distillation using thermodynamic geometry; in S. Sieniutycz, A. De Vos (eds.): Thermodynamics of energy conversion and transport (Springer, 2000), p. 319-331.

89 FF16P Studies of Micro Structures in Chalk Using X-ray Tomography

By L.P. Sperling 1, and

S. Kynde 1, I. S´anchez 2, T.H. Jensen 1, S. Stipp 2, R. Feidenhans’l 1

1 Niels Bohr Institute, University of Copenhagen 2 The Department of Chemistry, University of Copenhagen

Today it is not possible to extract more than 25-50% of the oil contained in the chalk layers of the North Sea, partly because the oil sticks to the micro structures of the chalk.[1] This project is a part of the Nano-Chalk project, with the long term goal to improve the process of oil extraction. By studying chalk using X-ray tomography we are able to see micro structures in chalk. Our measurements were done at the TOMCAT X-ray tomography beamline at the Swiss Light Source at the Paul Scherrer Institut in Switzerland, where we could image our chalk samples with a voxel size of 350 nm. The method is non destructive, which enable us to measure the same sample under different conditions, for instance showing how water and dodecane penetrates into the sample.

[1] http://www.hoejteknologifonden.dk/index.php?id=41

90 FF17P Microstructure of (112) GaAs nanorods grown by MBE

By Lars P. Hansen 1 and

S.A. Jensen 1, E. Johnson 1,2, C.B. Sørensen 1, J. Nyg˚ard 1

1 Niels Bohr Institute, Nano Science Center, University of Copenhagen, Denmark 2 Department of Materials Research, Risø DTU, Roskilde, Denmark

GaAs semiconductor nanorods have been grown at 515 ◦C by MBE on (100) B As terminated GaAs wafers with Au nanoparticles acting as nucleation- and catalyst sites.

In the present experiments a small fraction – about 5% – of the nanorods were found to grow in directions dif- ferent from the preferred (111) B. Using a cleaved wafer in the SEM it was possible from the knowledge of the wafer geometry to determine the growth direction of these rods which were found to grow along the (112) A directions.

The (112) rods are about 10 times longer than other rods in the growth and often appear to have mixed wurtzite- zincblende structure and a special lancet-shaped blade-like microstructure where part of the blade has a very smooth and straight edge. In other cases the (112) rods would have a perfect wurtzite structure containing lamellae of zincblende a few monolayers in thickness parallel to the rod axis.

Formation of unusual nanorods may be due to local differences in the growth conditions either from defects in the wafer surface or due to local strain variations. This should be studied further to elucidate details in the growth processes leading to occurrence of anisotropic crystal growth.

91 FF18P Localised Modes in Mono-Atomic Gold Wires

By Mads Engelund and

Mads Brandbyge Antti-Pekka Jauho

DTU Nanotek The miniturisation of circuits is ever continuing, but now the components have become so small that new theoretical tools need to be developed. The transport through the system, consisting of only one molecule, can be correlated across the molecule. This makes it important to have a very accurate description of the leads as well. To have an accurate description of molecular transport it is not enough to look at just electron transport or just heat transport, since the small dimensions of the system make the position of every atom important. This means that heat transport, which consists of atomic vibrations, couple strongly with electron transport. It is the aim of this project to calculate heat and current transport with this coupling using only ab-initio parameters. All in all, we hope to give a good description of currents in realistic systems and under realistic conditions.

92 FF19P Fabrication and measurements on coupled photonic crystal cavities

By Martin Schubert and

Henri T. Nielsstrup, Lars Hagedorn Frandsen, Toke Lund Hansen, Jeppe Johansen, Peter Lodahl, Kresten Yvind, and Jørn M. Hvam

DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Building 343, 2800 Kgs. Lyngby, Denmark

Quasi-three dimensional photonic crystals can be realized by fabricating thin membranes of high index material hanging in air patterned with sub-micron holes. The optical confinement in the plane of the membrane is achieved though a photonic band gap while total internal reflection confines the light out of the plane. Introducing defects into the photonic crystal give rise to defect states in the form of small confined modes. By embedding an active gain medium like quantum dots into the membrane makes it possible to realize lasers with ultra-small mode volumes and low thresholds. Unfortunately single cavity photonic crystal lasers have also a low output power. A promising way to increase the output power while keeping a low threshold is to couple a large number of cavities [1]. We have successfully fabricated several coupled cavity systems and measured on them in order to investigate the behaviour of the coupled systems and the interaction between coupled cavities depending on their relative coupling to each other.

[1] H. Altug, J. Vuckovic, “Two-dimensional photonic crystal resonator arrays”, Appl. Phys. Lett. 84, 161-163 (2004)

93 FF20P A Circuit Model for the Merging of Dielectric alpha- and beta-relaxation

By Nesli Saglanmak and

Kristine Niss, Jeppe Dyre, Niels Boye Olsen.

DNRF Centre “Glass and Time”, IMFUFA, Department of Sciences, Roskilde University, Denmark The dielectric relaxation spectra of liquids close to the glass transition is dominated by the structural alpha re- laxation. However, many liquids also exhibit a clearly resoluted secondary relaxation, referred to as the slow beta relaxation or the Johari-Goldstein process. The role of the beta relaxation including its relation to the alpha relaxation is not well understood and a subject to active studies. The first question in this context is whether it is possible to make a meaningful separation of the two processes in order to be able to study the ’pure’ individual processes. There are two traditional routes to such a separation, either to consider the total spectrum as a sum of two processes or to consider it as a convolution of the two processes. In this work we present an electrical network model which results in a new view on the merging of the alpha and the beta processes. We compare the model to new dielectric data on two glass-formers and get good fits with reasonable parameters. We moreover discuss the charecteristic features of the alpha-beta seen in the new model and in data.

94 FF21P McStas 1.12 – 10 year anniversary of danish excellence in simulation of neutron scattering

By Peter Willendrup and

Erik Knudsen Emmanuel Farhi Kim Lefmann

Risø DTU, Frederiksborgvej 399, DK-4000 Roskilde, Denmark Institut Laue-Langevin (ILL), 6 rue J. Horowitz, BP 156, 38042 Grenoble Cedex 9, France NBI, Universitetsparken 5, DK-2100 Copehagen, Denmark

Since release 1.0 in october 1998, the McStas neutron ray-tracing simulation package has been hosted at Risø in strong collaboration with the leading european neutron facility at ILL, Grenoble.

During its lifetime, McStas has evolved to become the world leading software in the area of neutron scattering simulations for instrument design, optimisation, virtual experiments and science.

Celebrating our 10 successful years in the neutron Monte-Carlo buisness, this poster draws an outline of the McStas software package and recent achievements.

95 FF22P Growth and characterization of hematite nanorods for use in solar cells

By S. A. Jensen 1 and

J. R. Maiolo III 2 A. Fitch 2 N. S. Lewis 2 E. Johnson 3,4 Jesper Nyg˚ard 3 Kristine Kils˚a 5

1 Nano Science Center, University of Copenhagen, Denmark, 2 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA 91125, 3 Niels Bohr Institute, Nano Science Center, University of Copenhagen, Denmark, 4 Department of Materials Research, Risø DTU, Roskilde, Denmark, 5 Department of Chemistry, Nano Science Center, University of Copenhagen, Denmark, Hematite (alpha-Fe2O3) nanorods were grown on indium-tin oxide coated glass substrates from an aqueous solution of F eCl3 and NaNO 3 with varying growth parameters (growth time, growth temperature, reactant concentration, pH of precursor solution, substrate type, and substrate cleaning procedure) based on a method described by Vayssieres et al., Chem. Mater., 2001. Thin rods of diameters sim5 nm are observed to assemble in bundles of sim50 nm that grow on the substrate in random directions. ∼ The geometry of the nanorods enables light to be absorbed along the long axis of the rod, ensuring a high absorption, while the minority carriers only need to diffuse a short distance in the radial direction to reach the hole carrying phase. Furthermore, the path of the photo excited electron is straight and does not cross any grain boundaries, which should present an advantage over multicrystalline colloidal films. The morphology and crystal structure of the synthesized nanorods is characterized by SEM, TEM, and HRTEM, and their chemical composition is investigated using energy dispersive spectrometry (EDS). The optical absorption and photo electrochemical properties of the rod arrays are investigated and compared to results from the litterature.

96 FF23P Exciting Excitations in Magnetic Nanofoam – Poster

By Sonja Rosenlund 1 and

Adrian Hill 2 Niels Vesterg˚ardJensen 3 Kim Lefmann 1 Andrew Harrison 2,4

1 University of Copenhagen, Niels Bohr Instituttet, Denmark 2 The University of Edinburgh, Centre for Science at Extreme Conditions & School of Chemistry, UK 3 Risø-DTU, Dept. of Materials Research, Denmark 4 Institute Laue-Langevin, Grenoble, France

The large internal surface area of mesoporous solids of transition metal oxide provide a perfect arena for catalytic processes to take place and a huge effort has been put into synthesising these so-called nanofoams [1]. These unique samples open for the study of interesting fundamental questions related to the novel dimensionality of the system. Here we present the first study of magnetic dynamics in the antiferromagnetically ordered α-Fe2O3 (hematite) nanofoam.

With a pore-size of 2 – 15 nm and a wall thickness of less than 8 nm the sample is indeed nanosized, and the confined dimensionality of the nanofoam walls significantly changes the magnetic structure compared to both bulk hematite and hematite nanoparticles [2]. The nanofoam possesses the same long-range magnetic order as found in bulk hematite, yet the Morin transition observed in bulk hematite is suppressed due to size-effects as found in hematite nanoparticles [3].

To gain a better understanding of the magnetism of the nanofoam we have studied magnetic dynamics by means of inelastic neutron scattering. With the ability to monitor fast dynamics inelastic neutron scattering has proven an efficient method for the study of superparamagnetic relaxation and collective magnetic excitations in antiferromagnet- ically ordered nanosized structures [4]. We observe similar magnetic dynamics as seen in hematite nanoparticles [4, 5] but with additional long-range order and compare the results to dynamics observed in interacting 8 nm hematite nanoparticles [6].

[1] F. Jiao et al, J. Am. Chem. Soc. 128, 5468, 2006 [2] I. V. Golosovsky et al, Solid State Comm. 141, 178, 2007 [3] F. Bødker et al, Phys. Rev. B 61, 6826, 2000 [4] M. F. Hansen et al, Phys. Rev. Lett. 79, 4910, 1997 [5] S. N. Klausen et al, Phys. Rev. B 70, 214411, 2004 [6] L. Theil Kuhn et al, Phys. Rev. B 74, 184406, 2006

97 FF24P kHz Microfluidics- Extended quivalent circuit analysis and its frequency dependent phenomena

By Søren Vedel 1,2 and

Henrik Bruus 1 Laurits Højgaard Olesen 2

1 = DTU Nanotech, Kongens Lyngby 2 = Diabetes Research Unit, Novo Nordisk, Hillerød Equivalent electric circuits have proved effective as low order models of microfluidic systems through the one-to-one mathematical analogies existing between fluidics and electronics. However, regular equivalent circuit analysis is only a mediocre tool for describing dynamic flow behaviour, since the analogies are derived from simplified considerations rarely satisfied.

Equivalent circuit modelling has been applied to a simple microfluidic system and has been extended through an- alytical solutions to the Navier-Stokes equation for pulsatile flow, revealing a frequency dependence on the resistive term caused by a fluidic “skin effect”, which causes noticeable deviations between the regular and extended models. The effects of resonance will be considered.

98 FF25P Magneto-electric effect in LiNiPO 4

By T.B.S. Jensen 1, and

N.H. Andersen 1 N.B. Christensen 1,2, M. Kenzelmann 2,3, H.M. Rønnow 2,4, C. Niedermayer 2, K. Lefmann 1,5, J. Schefer 2, M.v. Zimmermann 6, J. Li 7, J.L. Zarestky 7, D. Vaknin 7

1 Materials Research Department, Risø National Laboratory of Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark, 2 Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, CH-5232 Villigen, Switzerland, 3 Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland, 4 Laboratory for Quantum Magnetism, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland, 5 Niels Bohr Institute, Universitetsparken 5, 2100 Copenhagen, Denmark, 6 Hamburger Synchrotronstralungslabor at Deutsches Electronen Synchrotron, 22603 Hamburg, Germany, 7 Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Materials with both magnetic and ferroelectric phases, known as multiferroics, have received growing attention in recent years. One group of multiferroics where the magnetic and electric properties are strongly coupled are the so-called magneto-electric (ME) compounds. These systems have ferro- or antiferromagnetic (FM or AFM) phases where the application of a magnetic field will induce electric polarization. The reverse is also true; applying an electric field will induce a macroscopic magnetization. The lithium-phosphates, Li extitMPO 4, where extitM=Mn, Fe, Co, Ni, have the strongest magneto-electric effects of any non-composite materials – yet the mechanisms connecting the magnetism and the electrical polarizations in these systems are not known.

We have performed a series of neutron experiments on a single crystal of LiNiPO 4. This compound is known to have a commensurate (C) AFM phase below 20.8 K, and to have long-range incommensurate (IC) order between 20.8 and 21.8 K. In elastic experiments we have determined the magnetic structure of the IC phase, and have corrected the existing picture of the C structure. We have also applied a magnetic field along the crystallographic c-axis, deter- mining the magnetic HT-phase diagram and the corresponding magnetic structures. Based on the detailed magnetic structures we propose a possible microscopic explanation for the ME effect in LiNiPO 4.

99 FF26P Thermal Effusion in a Spherical Geometry at the Glass Transition.

By Tage Christensen and

Bo Jakobsen Niels Boye Olsen

DNRF centre “Glass and Time”, IMFUFA, Department of Sciences, Roskilde University, Denmark.

It is possible to supercool most liquids avoiding crystallization on cooling below the melting point. As temperature is lowered viscosity raises and at a viscosity of 1012Pas the liquid begins to behave like an elastic solid. It is then characterized as a glass. At the glass transition almost all properties show time dependence due to structural relax- ation. This is also true for the specific heat. The time dependence is conveniently studied in the frequency domain using socalled AC-calorimetry giving a complex frequency dependent specific heat c(ω). Most methods use excitation p of thermal waves [1] and relies on the heat diffusion equation to get the effusivity e(ω) = λc(ω). Subsequently c(ω) can be found and is interpreted as to be the isobaric one. However we have recently shown that this is not valid when viscous liquids enters the viscoelastic regime [2]. Instead the socalled longitudinal specific heat will be found. We present measurements of this quantity measured by a novel method in spherical geometry. [1] N. O. Birge, Phys. Rev. B34,1631 (1986). [2] T. Christensen, N. B. Olsen and J. C. Dyre, Phys Rev. E75, 04502-1 (2007).

100 FF27P 100 ps time-resolution in a sports-bag

By Thomas Nørskov Nielsen Centre for Molecular Movies Niels Bohr Institute Time-resolved X-ray diffraction and reflectivity are novel methods for determining the structural evolution of stuff on time-scales from 200 fs and above. Presently, experiments can only be done at a limited number of facilities in- cluding a few highly specialised synchrotron beamlines. The time-resolution aobtained at most of these beam-lines is limited by the duration of the local X-ray bunches, ranging from 80 ps to 400 ps.

This poster presents an easy-to-assemble detector system, which can be carried around the world in a sports-bag. It is based on commercially available components and has an inherent time resolution of 120 ps. Thus equipped, we can in principle use any synchrotron beamline for time-resolved X-ray studies af processes taking place on this time-scale, e.g. solid-liquid-solid phase transformation (diffraction) and layer dynamics in multilayered systems (re- flectivity).

101 FF28P Inductively coupled resonant pressure sensor for intra-abdominal pressure monitoring

By Thor Ansbæk and

Erik V. Thomsen

DTU Nanotech Department of Micro- and Nanotechnology Technical University of Denmark Kongens Lyngby Denmark Microsystems have attracted wide attention in the biomedical society for their inherent ability to be implanted as part of medical devices in humans and animals. Investigations have been long underway in the fabrication of an inductively coupled pressure sensor for measuring the bladder pressure wirelessly [1]. By avoiding the usual cather- ization the patient is able to move freely, while allowing continuous monitoring. This has numerous applications, e.g. the treatment of neurogenic detrusor overactivity (NDO) which can cause kidney failure.

A sensor design is proposed which have minimum form-factor, while maintaining a high quality factor of the res- onant circuit. The design incorporates a hermetically sealed cavity with an electrically connected diaphragm and inductor coil fabricated on a low-loss substrate. A prototype will be fabricated by silicon microtechnology on insu- lating substrates and subsequently tested in vivo. The reflected impedance of the sensor can be probed by a nearby inductor coil and by various electronic components (e.g. a voltage-controlled oscillator or phase-locked loop) the res- onant frequency can be extracted and the change related to a change in pressure.

The project is done in collaboration with Center for Sensory-Motor Interaction (SMI), Aalborg University aiming at developing a biocompatible wireless pressure sensor for detection of the on-set of bladder contraction.

102 FF29P Robust fabrication of nanogaps for nanoelectronics

By Torben M. Hansen and

Henrik H. Henrichsen Peter Bøggild

DTU Nanotech, Technical University of Denmark Because of process variations it is difficult to consistently fabricate electrode gaps in the range below several tens of nanometers. We have developed a technique for robustly creating nanogaps in the sub-10-nm range. Using e-beam lithography and metal lift-off, structures with gradually varying spacing were created. It is then possible by electrical measurements to induce which of the gaps have spacings the range of interest. This allows us to quickly collect statistical information on process variation on both the intra-wafer scale and the wafer-to-wafer scale. The developed method further allows us to measure how the electronic properties depends on electrode spacing in the 5 nm to 100 nm regime. We have used this to investigate the interface properties of metal to para-hexaphenylene thin films contact.

103 FF30P Strong coupling of a quantum emitter to surface plasmon polaritons

By Yuntian Chen 1, and

Torben Roland Nielsen 1, Peter Lodahl 1, Jesper Mørk 1,

1: DTU Fotonik, Department of Photonics Engineering, Oersteds Plads Building 343 DK- 2800 Kgs. Lyngby , Denmark Recently, surface plasmon polaritons (SPPs) have spurred enormous interests for their relevant roles in sub- wavelength optics and their applications in sensing, near field imaging and waveguiding. The squeezing of the elec- tromagnetic field along the metal-dielectric interface due to boundary condition constraints gives a huge enhancement of the local density of the optical states. Consequently the decay rate of a dipole emitter, which is close to the metallic-dielectric interface, will be strongly modified. We study the strong coupling of surface plasmons supported by a metallic nanowire with quantum emitters, which can be potentially utilized as single-photon sources [1]. The dyadic Green function of the cylindrical metallic waveguide is constructed based on the eigenfunction expansion by a finite element method. The different components of the dyadic Green function, the longitudinal part and the transverse part ( which can be further divided into radiation modes and guided modes of the metallic waveguide), are orthogonal and obey a closure relation determined by the wave equation of the nano-sized waveguide. These modes of the waveguide determine the decay channel, into which the single photon can be emitted when the emitter decays. Our calculations show that the quantum emitter can be coupled efficiently to the surface plasmons, i. e., a single photon will be injected into the plasmonic mode with high probability when the quantum emitter decays.

1. D. E Chang, A. S. Sørenson, P. R. Hemmer, and M. D. Lukin, Phys. Rev. Lett., 97(2006), 053002

104 Nuclear and high energy physics

NF1 W mass measurement with the ATLAS experiment at the LHC

By Esben Klinkby Niels Bohr Institute There is little doubt that LHC will bring insight with respect to the understanding of the universe on the funda- mental level. In particular, it is anticipated that light will be shed on the origin of mass which according to our current understanding proceeds via the Higgs mechanism. Either the corresponding particle; the Higgs boson is discovered by the LHC experiments, or its existence will be strongly disfavoured. In either case, a key measurement to understand the origin of mass, is the W boson, since it is intimitely linked to the Higgs mechanism. By precise measuring the W boson mass, the allowed mass range for the Higgs boson can be constrained, both within the Standard Model and in its various extensions. Thus, regardless of the results of the Higgs search, a precise determination of the W mass is of paramount importance, and in this presentation methods are presented aiming at measurering the W mass to the highest possible precision with the ATLAS experiment.

105 NF2 The ALICE Potential for Discovering new Physics at LHC in pp collisions

By P. Christiansen 1, and for the ALICE Collaboration.

1 Lund University, Sweden The ALICE experiment at LHC is optimized for the study of heavy ion collisions, but will also study pp collisions from the start up of LHC.

In this talk I will give a brief overview of the ALICE main detectors, focusing on the large 88 m**3 ALICE Time Projection Chamber (TPC), which is the main tracking detector in the central barrel (—eta— ¡ 1).

I will then compare the ALICE experiments capabilities in pp collisions to those of the other LHC experiments, and show that for a special class of new particles, stable heavy charged particles (m ¿ 100 GeV/c**2), the ALICE experiment has a complementary coverage. These particles are predicted by some models of physics beyond the stan- dard model (SM) with relative high cross sections, e.g., R-hadrons (gluino + quarks) in split-SUSY.

If these particles exist their characteristics will be that they have large momenta, but are slowly moving at cen- tral rapidities (velocities in the range of 30-90% of the speed of light) and this allows them to be directly separated from SM particles via the dE/dx in the TPC and the time-of-flight.

106 NF3 Search for Non-Commutative Geometry in the ATLAS experiment using dilepton events

By Peter Lundgaard Rosendahl A Non Commutative extention to the Standard Model(SM) of Particle Physics is studied. This model could be tested at the ATLAS experiment at Large Hadron Collider expected to start this summer at CERN. NC Space-Time could enable us to merge Quantum Field Theory and General Relativity by introducing a commutation relation between the position operators [xµ, xu] = i, θµu and hereby also introducing a minimum length scale. Using the Seiberg Witten maps and the Moyal product we are able to construct a NC Standard Model. This will lead to new Gauge Boson Cou- plings enabling this theory to be tested by looking at the angular distribution of γ’s in Zgamma events at the ATLAS.

107 NF4 Search for long lived KK-gluons at the LHC using the ATLAS detector

By Simon F. Jørgensen 1 1 Niels Bohr Institutet A direct implication of Universal Extra Dimensions, and some compactification scenarios for warped extra di- mensions, is the presence of excited states of the standard model (SM) particles, namely Kaluza-Klein (KK) states or KK-particles. This excitation is, in our 3+1 dimensional world, seen as an extra mass term to the else ordinary SM-particle.

In this study the focus is, in particular, on the possible detection of long lived KK-gluons in ATLAS at the LHC. The definition of long lived in this context is that they do not decay inside the ATLAS detector volume and hence are treated as heavy stable hadrons.

108 NF5 Microwave Diagnostic For Fusion Energy Research

By Vedran Furtula1 and

M.Salewski1, S.B.Korsholm1, F.Leipold1, S.K.Nielsen1, H.Bindslev1, P.Michelsen1, F.Meo1,2, M.Jessen1, J.Holm1, S.Nimb1

1 Risø National Laboratory – DTU, OPL-PLF, Denmark 1 CTS-AUG, IPP Institute of Plasma Physics, MPG-Research Center, Germany An introduction to current fusion energy research is given, emphasizing basic concepts of fusion plasmas confined by strong magnetic fields. A joint international research and development project has been started and is set out to build a machine on the plasma confinement principle with the vision to obtain more energy from fusion than is required for the operation of the device. This 5 billion Euro international project ITER is currently being built in Cadarache, France. One of the scientific cornerstones of the ITER mission is to study the physics of fast particles generated in the fusion process. For this purpose, a number of diagnostics are being developed which can measure these dynamics. Collective Thomson scattering (CTS) can fulfill this research objective at ITER by the use of electromagnetic waves in the millimeter range generated by 1 MW gyrotrons at 60 GHz. A CTS system for ITER is being developed at Risø DTU. One of the most critical components in a transmission line for microwaves in ITER is a set of mirrors. A full-scale mock-up of these mirrors has been constructed. We discuss software tools for 3-D simulations and techniques to characterize the microwave beams, e.g. network/spectrum analyzer, robot etc.

109 NF6 Search for New Physics Using High Mass Tau Pairs in ATLAS at the LHC.

By Zofia Czyczula Niels Bohr Institute Although the Standard Model (SM) is a well established theory applicable over a wide range of conditions, it is believed to be an effective low-energy approximation to a more fundamental theory which should appear at a scale of 1 TeV. The Large Hadron Collider (LHC), with center of mass energy of 14 TeV, will begin to operate in summer 2008 and therefore some Beyond Standard Model (BSM) theories will have the first chance to be tested. Many heavy BSM hypothetical particles couple preferentially to third generation of fermions. Based on Monte Carlo simulated data I will present prospect of observability of resonant production of tau lepton pairs with large invariant mass in ATLAS. Limits, set by other High Energy Physics experiments, on the production of heavy particles will be shortly reviewed.

110 NF1P Simulation of scintillor plates for DUKS

By Sune Jakobsen Niels Bohr Institutet DUKS (Danish Educational Cosmic Radiation Project) is an attempt to introduce Danish high school students to scientific research and at the same time produce experimental data on high energy radiation from outer space by detecting muons impacting Earth. By including the high schools, a large number of measuring points with large mutual distance are achieved, and therefore it will be possible to register airshowers from very high energy cosmic particles, which origin still is a mystery. The original idea was that each scintillator detector only would be able to register if particles (primary muons) passed the detector. But it is interesting to detect the density of particles passing because the number of passing particles will increase towards the center of the shower. It is being considered to add an analog-digital-converter (ADC) to measure the amount of energy absorbed in the scintillator plate, and thereby measure the number of particles which passed. To optimize the choice of ADC, I have simulated (in Geant 4) the energy absorption in a scintilltor plate to determent the required resolution of the ADC.

111 KF1P Preliminary studies of disturbances in the magnetic field measurements in Brorfelde caused by DC current in Baltic Cable

By C. Fox Maule and

J. Matzka L.W. Pedersen A. Nilsson

Danmark Meteorologiske Institut The magnetic field is continuously measured with high accuracy at the Geomagnetic Observatory in Brorfelde for global mapping and monitoring of the Earth’s magnetic field. Recently we discovered that long distance DC power lines cause disturbances in the magnetic field measurements. We have identified two power lines, the Kontek line running from Bjæverskov to Rostock and the Baltic Cable running from Malmø to L¨ubeck, as the causes of the disturbances. As the power lines both run continuously and often with similar variation pattern it is difficult to separate the contributions from the two power lines. However, due to maintenance the Kontek line was shut down from 22nd february to 17th april 2008, providing an opportunity to study the contribution from the Baltic line separately. Here we present the first results of this study.

112 KF2P Alternative interpretation of combined backscatter and humidity measurements of stratospheric particles during the SCOUT-AMMA balloon campaign

By J.K. Nielsen 1 and

N. Larsen 1 T. Christensen 1 S. Khaykin 2 J.-P. Pommereau 3

1 Danish Meteorological Institute 2 Central Aerological Observatory, Russia 3 Service d’A´eronomie du CNRS, France Analysis of Wyoming Backscatter Sonde data from Niamey, August 23, 2006 shows that there was indeed a distinct particle cloud above the tropopause at 18 km. The backscatter signature is consistent with relatively small solid particles of radius = 0.5- 10 µm and the Lyman alpha Flash B hygrometer measured a distinct water vapour sub- saturation with respect to ice (saturation ratio less than 0.5). Radar images and MCS- tracking images, overlayed with ECMWF back trajectories, show that there were no deep convective overshoot immediately upwind from the observation point, which implies that the particles must have been there for at least 4-5 hours, and possibly longer. This is a mystery because 0.5-10 µm ice particles should sublimate within a few minutes under these circumstances. We suggest that the observed particles could be stabilized by electric charge.

113 Dansk Optisk Selskab

114 Principles and applications of a speckle-based wavefront sensor

Percival F. Almoro* and Steen G. Hanson Danish Technical University Fotonik, Department of Photonics Engineering, Roskilde 4000, DK *[email protected]

The motivation for this study is to carry-out interferometric applications using phase retrieval which affords a simple setup. The wavefront sensor has 3 components: 1) diffuser, 2) speckle patterns, and a 3) phase retrieval algorithm. A coherent test wavefront incident on a diffuser facilitates the formation of a speckle field. The sampled speckle patterns are input in a phase retrieval algorithm to reconstruct and compare test wavefronts. In this presentation, basic principles of the algorithm and applications of the technique in deformation analysis and angular displacement measurements are presented.

Fig. 1. Setup. A test wavefront incident on a phase diffuser generates a volum e speckle field. Axially-displaced speckle intensity m easurem ents are input in an algorithm based on the wave propagation equation.

Fig. 2. Surface deform ation analysis. (a) Retrieved Fig. 3. Angular displacement phases for various deform ation states. (b) Phase m easurem ent. Differences of retrieved differences. phases for planar wavefronts with increasing angular displacem ents. Localized Field Enhancements in Fractal Shaped Periodic Metal Nanostructures

Jonas Beermann1,*, Ilya P. Radko1,2, Andrey B. Evlyukhin3, Alexandra Boltasseva4 and Sergey I. Bozhevolnyi1,2

1Institute of Signals, Sensors and Electrotechnics, University of Southern Denmark 2Department of Physics and Nanotechnology, Aalborg University, Aalborg Øst, Denmark 3Department of Physics and Applied Mathematics, Vladimir State University, Russian Federation 4Department of Communications, Optics & Materials, Technical University of Denmark

Fractal shaped structures (extending over ~ 100 × 100 μm2) formed with a 100-nm-period square lattice of gold nanoparticles (height ~ 50 nm, diameter ~ 60 nm) placed on a 50-nm-thick gold film are characterized using far-field nonlinear scanning optical microscopy, in which two-photon photoluminescence (TPL) excited with a strongly focused laser beam (in the wavelength range of 730 - 790 nm) is detected. Spatial locations of nanoparticles within the fractal structures are calculated using part of the Mandelbrot fractal geometry and defined with electron-beam lithography, resulting thereby in reproducible nanoparticle clusters of practically all possible shapes within the available spatial range (i.e., from 100 nm to 100 µm).

(a) (b) Fig. 1. Pseudo-color optical (a) FH and (b) TPL images FH TPL of the fabricated fractal shaped structure of 60-nm- diameter gold particles. The used excitation wavelength (FH) was 730 nm and the polarization configurations are indicated by a pair (incident FH, detection) of colored arrows on the optical images. The maximum TPL signal in (b) was ~12k counts/s obtained at 1.2 mW incident power. 20µ m

Min Max

TPL images obtained for all wavelengths in the laser range exhibit diffraction-limited (~ 0.6 µm) bright spots corresponding to intensity enhancements of up to ~170, whose positions are dictated by the incident light wavelength and polarization. We relate these field enhancements to the occurrence of constructive interference of surface plasmon polaritons (SPPs) excited by the incident radiation (due to scattering by nanoparticles) and partially reflected by fractal shaped boundaries due to a difference in the SPP effective refractive index at a flat and periodically corrugated gold surface. This conjecture on SPP refractive index difference has been verified with observations (using leakage radiation microscopy) of SPP focusing by circular and waveguiding by rectangular areas filled with periodically arranged nanoparticles. Furthermore, these findings are supported by considering the polarization dependent SPP propagation in TPL images obtained near round and apparently SPP defocusing fractal boundaries. In addition, TPL bright spots where also found at the fractal boundaries, especially in less dense outer branches of the fractal shape and related to multiple scattering between individual nanoparticles. We supplement the characterization of these areas with relevant numerical simulations using the total Green dyadic, including excitation of SPPs. Comparing TPL intensities from the fractal structure to that of an individual particle, the used simulation provide a qualitative prediction of the intensity enhancement levels (~220) obtainable from also less ordered metal nanostructures. Finally, we have obtained experimental TPL images of a large specially shaped defect leading to strong intensity enhancements of up to ~210 at a rather broad resonance

*Corresponding author: [email protected] Correlation measurement of squeezed light

L. A. Krivitsky1,2, U.L. Andersen2, R. Dong2, A. Huck1, Ch. Wittmann2 and G. Leuchs2 1- Department of Physics, Technical University of Denmark, 2800 Lyngby, Denmark 2- Max Plank Research Group, University of Erlangen Nurnberg, 91058 Erlangen, Germany

We have demonstrated an implementation of the correlation measurement technique (Hanbury-Brown and Twiss type experiment) to the characterization of the polarization squeezed light source. We have shown that the sign of the covariance coefficient is determined by the statistics of the incoming light state, representing in this way a useful tool for studying squeezed light. Moreover, in contrast to the standard approach for the measurement of the squeezed light (direct detection of variation of sum and difference photocurrents), the correlation measurements allow to eliminate any kind of electronic noise, which become a crucial issue in experiments with weak squeezed light. Generation of Non-Classical Surface-Plasmon-Polaritons

1, 2 2 2 1 1 Alexander Huck, ∗ Stephan Smolka, Peter Lodahl, Alexandra Boltasseva, Jiri Janousek, and Ulrik L. Andersen 1Department of Physics, Technical University of Denmark, Building 309, 2800 Lyngby, Denmark 2DTU Fotonik, Technical University of Denmark, Building 345V, 2800 Lyngby, Denmark (Dated: June 2, 2008)

Surface plasmon polaritons (SPPs) have strongly attracted the attention of the quantum optics community due to their unique properties. For instance, SPPs are predicted to couple to single emitters [2, 3] allowing huge non-linear interaction on the single photon level [4]. The first plasmon experiment in the quantum optics regime demonstrates the preservation of entanglement under plasmon assisted transmission through sub-wavelength holes [1]. What is still missing is a complete quantum characterization of SPPs. In our contribution we investigate the efficient generation of non-classical long-range SPPs in the continuous variable regime by exciting them with a squeezed optical light field. Our results show quantum fluctuations of up to 0.5dB below the shot noise limit, as presented in Fig. 1. −

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-0,5 Noise variance rel. to shot noise [dB] noise shot to rel. variance Noise

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FIG. 1: Measured noise variance of long-range SPPs relative to the shot noise limit. The fluctuations below the shot noise level clearly show the non-classical property of the excited SPPs.

[1] E. Altewischer et al., Nature (London) 418, 304 (2002); E. Moreno et al. Phys. Rev. Lett. 92, 236801 (2004). [2] D.E. Chang et al., Phys. Rev. Lett. 97, 053002 (2006). [3] A.V. Akimov et al., Nature (London) 450, 402 (2007). [4] D.E. Chang et al., Nature Physics 3, 807-812 (2007).

∗Electronic address: [email protected] Three-dimensional imaging and three-dimensional coordinate gathering in three- dimensional optical micromanipulation system

Jeppe Seidelin Dam*, Ivan Perch-Nielsen, Darwin Palima, Jesper Glückstad Danish Technical University Fotonik, Department of Photonics Engineering, Roskilde 4000, DK *[email protected]

We present a low cost three dimensional (3D) imaging solution in our three dimensional micromanipulation system. The imaging solution is capable of deducing 3D coordinates for multiple objects simultaneously in real time. The method described works with a single camera and a low cost, commercially available LED based projector. A variant of this method can be used to make stereoscopic images which the human brain can decode as a 3D structure by help of red/blue sterescopic glasses.

Figure 1: Angled illumination with different colors is used to make dual images of out of focus objects. The displacement between these colored shadows is proportional to the out of focus position.

Figure 2: Stereoscopic images of an assembly of trapped beads of various sizes. Second image shows image analysis of the first actual image. The last image shows how the analyzed image looks when a centered green illumination is added to the illumination seen in Fig. 1.

UV assisted rotational moulding of microstructures for high‐volume production of diffractive optical elements on foil

Lars R. Lindvold and Jan Stensborg Stensborg A/S Frederiksborgvej 399, Niels Bohr 4000 Roskilde Denmark

Abstract

We present the first commercially available system for in‐line printing of holographic microstructures as a part of a conventional 4‐colour printing machine for e.g. label printing.

The talk will focus on the challenges of transferring microstructures, by means of rotational micro‐ moulding and UV curable lacquers in a process known as Holoprint™ (see figure below), at a speed of 60 m/min with high fidelity.

Tranparent cylinder with mould

UV lamp with focusing lens

Structure forming nip

Micro surface relief

Foil with UV curable lacquer(red) UV light is focused by a cylinder lens in the nip. UV curable lacquer is Detail of mould prior to mounting on applied to a substrate material and brought into contact with a transparent cylinder transparent mould wound around a cylinder. UV lacquer is cured in the line of focus, the nip, and the microsurface relief is replicated onto the substrate

The possible use of this technology as a generalised platform in industrial roll‐to‐roll (R2R) fabrication of microstructures will also be discussed.

Fractional decay of quantum dots in photonic crystals

Philip Kristensen (1), A. Femius Koenderink (2), Peter Lodahl (1), Bjarne Tromborg (1) and Jesper Mørk (1)

(1): DTU Fotonik, Department of photonics engineering, Lyngby, DK (2): FOM Institute for Atomic and Molecular Physics, Amsterdam, NL

Spontaneous emission dynamics represents a spectacular display of the quantum nature of light-matter interaction as it results directly from the coupling of a quantum emitter to the electromagnetic vacuum. Using novel materials (such as photonic crystals, see Fig. 1) it is possible to locally change the distribution of the vacuum modes and thus to change the spontaneous emission. In most cases the decay remains exponential, but with an altered rate. This effect is known as the Purcell effect. In certain special cases, however the decay may take on fundamentally different forms. In particular, a regime of so-called fractional decay has been pointed out. In this regime, the emitter coherently interacts with modes of low group Fig 1. Unit cell of an inverse velocity in such a way that it never fully decays, but rather opal photonic crystal. By remains in a superposition of the excited state and the ground carefully positioning quantum state (see Fig. 2). Whereas the Purcell effect has been shown dots within the crystal it is experimentally for quantum dots (QDs) in e.g. photonic crystals possible to control the , there is to date no demonstration of fractional decay. spontaneous decay dynamics

In this work we define a practical measure of the degree of fractional decay and use it to investigate if the effect will be observable for QDs in real photonic crystals in the presence of absorptive losses.

Fig2. Decay curves from a quantum dot in the photonic crystal for different material absorption. Grey curve shows the fractional decay in the case of zero loss. Material absorption (red and blue curves) changes the decay from a fractional type into a single exponential decay. Γ is the decay rate in vacuum. 0 Refracting surface plasmons with nanoparticle arrays Ilya P. Radko†, Alexandra Boltasseva‡ and Sergey I. Bozhevolnyi*,† †Department of Physics and Nanotechnology, Aalborg University, Skjernvej 4A, DK-9220 Aalborg Øst, Denmark ‡Department of Photonics Engineering, Technical University of Denmark, Bldg. 345v, DK-2800 Kongens Lyngby, Denmark *Institute of Sensors, Signals and Electrotechnics, University of Southern Denmark, Niels Bohrs Alle 1, DK-5230 Odense M, Denmark Integrated plasmonics operates with surface plasmon polaritons (SPPs) and is hoped to substitute integrated optics, which suffers from its components being bulkier than electronic ones, but in turn much faster than those [1]. The success of development of this relatively young branch of physics depends on the variety of active and passive components available for the integration. Plasmonics, having features of both photonics and electronics, in terms of operational elements bears more resemblance to optics since Bragg mirrors, waveguides, beam splitters, and interferometers are used. For instance, dielectric optical elements for surface plasmons, featuring such functionality as focusing, refraction, and total internal reflection, have previously been demonstrated [2]. In this work we investigate variously shaped periodic gold nanostructures on top of a gold film having period much smaller than the wavelength. The SPP waves propagating along the surface inside a periodic array of nanoparticles experience an increase in the effective refractive index [3], and, for the array periods considerably smaller than the wavelength, relatively weak out-of-plane scattering [4]. Using leakage radiation microscopy (LRM), we show that those structures act as a refractive medium for SPPs featuring the effective refractive index (ERI) of about 1.08. This means that they can be used to make components for plasmonics, similar to optical prisms, lenses, and optical-fiber waveguides.

Figure shows a LRM image of a SPP beam scattered by a 7.5-µm-diameter circular-shaped periodic structure. The periodic structure is formed by 50-nm-high and 60-nm-wide rounded-square gold bumps on top of a gold film.

[1] R. Zia, J. A. Schuller, A. Chandran, M. L. Brongersma, “Plasmonics: the next chip-scale technology,” Materials Today 9, 20-27 (2006). [2] A. Hohenau, J. R. Krenn, A. L. Stepanov, A. Drezet, H. Ditlbacher, B. Steinberger, A. Leitner, F. R. Aussenegg, “Dielectric optical elements for surface plasmons,” Opt. Lett. 30, 893-895 (2005). [3] S. C. Kitson, W. L. Barnes, J. R. Sambles, “Full photonic band gap for surface modes in the visible,” Phys. Rev. Lett. 77, 2670-2673 (1996). [4] T. Søndergaard, S. I. Bozhevolnyi, A. Boltasseva, “Theoretical analysis of ridge gratings for long-range surface plasmon polaritons,” Phys. Rev. B 73, 045320 (2006). Observing of spatial quantum correlations induced by multiple scattering of light

Stephan Smolka1, Alexander Huck2, Ulrik L. Andersen2, and Peter Lodahl1

1 DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Building 345V, 2800 Kgs. Lyngby, Denmark 2 DTU Physics, Department of Physics, Technical University of Denmark, Building 309, 2800 Kgs. Lyngby, Denmark

We investigate the transport of non-classical light through multiple scattering random media. So far almost all experiments in the multidisciplinary field multiple light scattering have concentrated on the transport of light intensity. In recent years the quantum nature of multiple scattered light has been considered by studying the photon fluctuations of the light [1]. It was predicted that fluctuations below the classical limit can survive multiple scattering and novel spatial quantum correlations can be induced [2]. In accordance with the Heisenberg uncertainty principle, photon fluctuations smaller than the classical limit can only be generated with non-classical light sources. Using squeezed light we performed the first experimental demonstration that non- classical fluctuations survive multiple scattering of light. The experiments are in excellent agreement with theory. Moreover we demonstrate experimentally that multiple scattering induces novel spatial quantum correlations, cf. Fig. 1.

Fig 1. Illustration of multiple scattering process leading to spatial quantum correlations. A non-classical light source illuminates a medium consisting of a random distribution of scatterers. The incoming light is split into a multitude of different trajectories that perform a random walk through the medium. The number of photons exiting the medium in a specific direction can be anti- correlated with the number of photons in another direction, and this correlation depends on the quantum state of light illuminating the medium.

References 1. P. Lodahl and A. Lagendijk “Transport of quantum noise through random media”. Phys. Rev. Lett. 94, 153905--153909 (2005). 2. P. Lodahl, A. P. Mosk, and A. Lagendijk “Spatial quantum correlations in multiple scattered light”. Phys. Rev. Lett. 95, 173901--173904 (2005).

Wavelength Selective Nanophotonic Components Utilizing Channel Plasmon Polaritons

Valentyn S. Volkov,1 Sergey I. Bozhevolnyi,1 Eloї1se Devaux,2 Jean-Yves Laluet,2 and Thomas W. Ebbesen2 1Institute of Sensors, Signals and Electrotechnics (SENSE), University of Southern Denmark, Niels Bohrs Allé 1, DK-5230 Odense M, Denmark. 2Laboratoire des Nanostructures, ISIS, UniVersite´ Louis Pasteur, 8 alle´e Monge, BP 70028, 67083 Strasbourg, France.

Channel plasmon polaritons (CPPs) are electromagnetic waves that are bound to and propagate along the bottom of grooves cut into a metal.1 They are expected to exhibit useful subwavelength confinement, relatively low propagation loss, and single mode operation1, 2 as well as efficient transmission around sharp bends.3 Our previous experiments showed that the CPPs at telecom wavelengths propagate over tens of micrometers along grooves in gold and exhibit strong subwavelength confinement4 along with low bend losses in large-angle S-bends and Y-splitters,5 thereby enabling the realization of ultracompact plasmonic components, such as Mach-Zehnder interferometers and waveguide-ring (WR) resonators.6 The results obtained with the above set of structures encouraged us to further exploit the potential of CPPs and to investigate more sophisticated and/or new functional plasmonic components. Here, we report the fabrication and investigation of CPP-based wavelength selective components operating at telecom wavelengths: a WR resonator-based add-drop multiplexer (WRR-ADM) composed of two 0.5-μm-wide and 1.3- μm-deep gold grooves combined with a 5-μm-radius ring resonator and a compact (3.75-μm-long) Bragg grating filter (BGF) comprised 0.5-μm-long wells milled with the period of 0.75 μm across a groove. High quality SNOM images of the components have been obtained in the wavelength range of 1425-1600 nm and analyzed to determine their characteristics.

(1) Novikov, I. V.; Maradudin, A. A. Phys. ReV. B 2002, 66, 035403. (2) Moreno, E.; Garcia-Vidal, F. J.; Rodrigo, S. G.; Martin-Moreno, L.; Bozhevolnyi, S. I. Opt. Lett. 2006, 23, 3447. (3) Pile, D. F. P.; Gramotnev, D. K. Opt. Lett. 2005, 30, 1186. (4) Bozhevolnyi, S. I.; Volkov, V. S.; Devaux, E.; Ebbesen, T. W. Phys. ReV. Lett. 2005, 95, 046802. (5) Volkov, V. S.; Bozhevolnyi, S. I.; Devaux, E.; Ebbesen, T. W. Appl. Phys. Lett. 2006, 89, 143108. (6) Bozhevolnyi, S. I.; Volkov, V. S.; Devaux, E.; Laluet, J.-Y.; Ebbesen, T. W. Nature 2006, 440, 508. Posters for the Annual Meeting for the Danish Optical Society:

DOPS 1 “A many-body model of semiconductor single-photon sources" Per Kær Nielsen, Torben Roland Nielsen, Peter Lodahl, and Jesper Mørk DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark

DOPS 2 "Influence of Pure Dephasing on Emission Spectra from Single Photon Sources" Andreas Næsby, Troels Suhr, Philip T. Kristensen and Jesper Mørk DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark

DOPS 3 Photonics Workstation for optical manipulation of microstructures with nano-features Ivan R. Perch-Nielsen, Jeppe S. Dam, Darwin Palima and Jesper Glückstad* *Contact: [email protected] DOPS 4 Field enhancement by nano-strip antennas investigated using two- photon photoluminescence scanning optical microscopy.

Sergey Novikov1, Jonas Beermann1, Thomas Søndergaard2, Alexandra Boltasseva3, and Sergey I. Bozhevolnyi1,2.

1 Institute of Sensors, Signals and Electrotechnics, University of Southern Denmark, Odense, Denmark.

2 Department of Physics and Nanotechnology, Aalborg University, Denmark

3 COM·DTU, Department of Communications, Optics & Materials, Technical University of Denmark, Kongens Lyngby, Denmark.

Abstract

The local field enhancement effects are of high interest, in general, for fundamental optics and electrodynamics and for various applied research areas, such as surface-enhanced Raman spectroscopy and microscopy including optical characterization of individual molecules. For investigation of the resonant field enhancement by gold nano-strip antennas we apply a high resolution method, namely two-photon photoluminescence scanning optical microscopy (TPL-SOM). It is know, that the sub-wavelength-sized metal particles (stripes) can exhibit optical resonances associated with resonant collective electron oscillations known as localized surface plasmons (LSP). Excitation of LSP results in the occurrence of pronounced extinction bands and in local field enhancement effects. The TPL-SOM technique is based on the circumstance that strongly enhanced local fields due to the excitation of LSP in gold nanostructures give rise to two-photon absorption, which in turn leads to a broad emission continuum generated by interband transitions of d-band electrons into the conduction band known as two-photon-excited photo luminescence (TPL) in gold. The resolution obtained in TPL images was better than 0.27 μm, FH ~0.4 μm for a stripe of 100 nm width. The field enhancement effect was obtained for p-polarisation (electric field across the strip) incident power 1 and 1.5 mW. The field enhancement effect was not observed for s- polarisation (as expected). Parameters of scanning were: 100-fold objective, scanning time (at one point) 100 ms, speed of scanning 20 μm/s. The area of scanning 3x14 μm2, the number of points 60x70 units, the step 50 nm (x-axis), 200 nm (y-axis). The experimental results obtained for gold 11–nm–thin strips of 50-600 nm widths placed on quarts and covered with index-matching oil are in excellent agreement with theoretical prediction and allows suggesting an optimization of parameters for improving field enhancement effects. DOPS 5 Theoretical investigation of two-wave mixing in a broad-area semiconductor amplifier with moving gratings

Mingjun Chi,1* Jean-Pierre Huignard,2 and Paul Michael Petersen1 1Department of Photonics Engineering, Technical University of Denmark, P.O. Box 49, DK-4 000 Roskilde, Denmark 2Thales Research & Technology, RD 128 91767, Palaiseau Cedex, France

Abstract: The two-wave mixing in a broad-area semiconductor amplifier with moving gratings is investigated theoretically, where a pump beam and a signal beam with different frequencies are considered, thus both a moving phase grating and a moving gain grating are induced in the amplifier. The coupled-wave equations of two-wave mixing are derived based on the Maxwell’s wave equation and rate equation of the carrier density. The analytical solutions of the coupled-wave equations are obtained in the condition of small signal when the total intensity is far below the saturation intensity of the amplifier. The results show that the optical gain of the amplifier is affected by both the moving phase grating and the moving gain grating, and there is energy exchange between the pump and signal beams. Depending on the moving direction of the gratings and the anti- guiding parameter, the optical gain may increase or decrease due to the two-wave mixing.

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Fig. 1. The two-wave mixing gain gTWM versus frequency difference between signal and pump δ with different anti-guiding parameter β. DOPS 6

High Power NIR Laser Bar with Improved Beam Quality

D. Vijayakumar, O. B Jensen and B. Thestrup

DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark

High Power diode laser bars are interesting light sources for e,g, the graphics industry due to their small physical size (in the order of cubic milli metres), high output power levels (up to 100W) and long life time (more than 10000 hours). But the major drawback of these laser sources is the poor beam quality in the freely running mode due to a broad emitting junction.

An efficient method for improving the beam quality of laser bars is Off Axis Spectral Beam Combining (Ref. 1). The light from the various emitters on the laser bar is combined using a reflection grating and made to travel in parallel to each other using an output coupler (Ref. 2). In addition to this, a few modes are fed back to the laser using a high reflective D shaped mirror. The experiments on a NIR laser bar yielded an output beam of 5.4 Watts of optical power at 20A of operating current and the measured M2 values of the combined beam from 13 emitters were 1.9 and 3.5 for the fast and the slow axis respectively. Comparing these results to that obtained from simple Spectral Beam Combining, the beam quality along the slow axis was improved by a factor of more than 30 without reduction in the output power.

References:

1. O.B. Jensen, B. Thestrup, P.E. Andersen, P. M. Petersen, Appl. Physics. B. 83, 225- 228 (2006). 2. V. Daneu, A. Sanchez, T. T Fan, H. K. Choi, G. W. Turner, C. C. Cook, Optics Letters, Vol. 25, No. 6, 405- 407 (2000). DOPS 7

Excitation of strongly confined dielectric-loaded surface plasmon-polariton waveguide modes at telecommunication wavelengths

ABSTRACT: The excitation of surface plasmon-polariton (SPP) waveguide modes in subwavelength dielectric ridges deposited on a thin gold film has been characterized and optimized at telecommunication wavelengths. The experimental data on the electromagnetic mode structure obtained using scanning near-field optical microscopy have been directly compared to full vectorial 3D finite element method simulations. Two excitation geometries have been investigated where SPPs are excited outside or inside the dielectric tapered region adjoint to the waveguide. The dependence of the efficiency of the SPP guided mode excitation on the taper opening angle has been measured and modeled. Single-mode guiding and strong lateral mode confinement of dielectric-loaded SPP waveguide modes have been characterized with the near-field measurements and compared to the effective index method model.

Med venlig hilsen

Tobias Holmgaard Department of Physics and Nanotechnology Aalborg University Skjernvej 4A DK-9220, Aalborg Øst Denmark Phone: +45 9940 9226 E-mail: [email protected] DOPS 8 DOPS 9 DOPS 10

Controlling the Emission Profile of a Nanowire with a Conical Taper

Niels Gregersen, Torben R. Nielsen and Jesper Mørk DTU Fotonik, Department of Photonics Engineering Technical University of Denmark, Building 343, DK-2800 Kongens Lyngby, Denmark

Julien Claudon and Jean-Michel Gérard CEA-Grenoble/INAC/Laboratoire Nanophysique et Semiconducteurs 17 rue des Martyrs, 38054 Grenoble Cedex 9, France

The influence of a tapering on nanowire light emission profiles is studied. We show that, for nanowires with divergent output beams, the introduction of a conical tapering with a small opening angle reduces the beam divergence and increases transmission. This results in a dramatic increase in the collection efficiency of the detection optics. For a realistic tapering and a modest numerical aperture, the collection efficiency is enhanced by more than a factor of 2. This improvement is ensured by the adiabatic expansion of the guided mode in the tapering.