SPIE Optics and Electronics Prague

18 - 21 April 2011
Prague Congress Centre
Prague, Czech Republic

Del Mar Photonics featured products

 Trestles LH Ti:Sapphire laser Trestles LH is a new series of high quality femtosecond Ti:Sapphire lasers for applications in scientific research, biological imaging, life sciences and precision material processing. Trestles LH includes integrated sealed, turn-key, cost-effective, diode-pumped solid-state (DPSS). Trestles LH lasers offer the most attractive pricing on the market combined with excellent performance and reliability. DPSS LH is a state-of-the-art laser designed for today’s applications. It combines superb performance and tremendous value for today’s market and has numerous advantages over all other DPSS lasers suitable for Ti:Sapphire pumping. Trestles LH can be customized to fit customer requirements and budget. Reserve a spot in our Femtosecond lasers training workshop in San Diego, California. Come to learn how to build a femtosecond laser from a kit DPSS DMPLH lasers DPSS DMP LH series lasers will pump your Ti:Sapphire laser. There are LH series lasers installed all over the world pumping all makes & models of oscillator. Anywhere from CEP-stabilized femtosecond Ti:Sapphire oscillators to ultra-narrow-linewidth CW Ti:Sapphire oscillators. With up to 10 Watts CW average power at 532nm in a TEMoo spatial mode, LH series lasers has quickly proven itself as the perfect DPSS pump laser for all types of Ti:Sapphire or dye laser. Ideal for pumping of: Trestles LH Ti:Sapphire laser T&D-scan laser spectrometer based on narrow line CW Ti:Sapphire laser New laser spectrometer T&D-scan for research  that demands high resolution and high spectral density in UV-VIS-NIR spectral domains - now available with new pump option! The T&D-scan includes a CW ultra-wide-tunable narrow-line laser, high-precision wavelength meter, an electronic control unit driven through USB interface as well as a software package. Novel advanced design of the fundamental laser component implements efficient intra-cavity frequency doubling as well as provides a state-of-the-art combined ultra-wide-tunable Ti:Sapphire & Dye laser capable of covering together a super-broad spectral range between 275 and 1100 nm. Wavelength selection components as well as the position of the non-linear crystal are precisely tuned by a closed-loop control system, which incorporates highly accurate wavelength meter.Reserve a spot in our CW lasers training workshop in San Diego, California. Come to learn how to build a CW Ti:Sapphire laser from a kit
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Permanent wavegides in glassy As4Ge30S66 induced by femtosecond filaments

Paper 8071-21 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 17:00 – 17:20

Author(s): Viktor M. Kadan, Ivan V. Blonsky, Institute of Physics (Ukraine); Oleh I. Shpotyuk, Lviv Scientific Research Institute of Materials (Ukraine) and J. Dlugosz Univ. de Czestochowa (Poland); Mihail S. Iovu, Institute of Applied Physics (Moldova); Petro Korenyuk, Institute of Physics (Ukraine)

We report the first observation of the femtosecond filaments and filament-induced permanent waveguides in bulky ChGs exemplified by a glassy As4Ge30S66. This wide-gap (3.0 eV) ChG has been synthesizes to reduce the two-photon absorption (2PA) which prevents the filament formation in more narrow-gap ChGs. We focus the femtosecond laser beam (110 nJ, 150 fs, 800 nm, 1 kHz) into a 3 mm thick sample at different pulse energies, exposures T, and positions of the beam waist inside the sample. The near-field beam profiles are measured on the exiting face of the sample. A reversible Kerr filament of 4.8 µm core diameter and of 1.8 mm length forms at T ≤ 10 s, while at T ≥ 25 s, a permanent waveguide appears. Two principal mechanisms are involved in the waveguide formation. First the Kerr filament forms, while the formation of the permanent waveguide occurs later due to the positive Δn build-up on the filament axis. A physical reason for the permanent index change is the generation of free carriers by 2PA in the filament core, which trigger structural transformation in the material. The Δn profile of the waveguide is numerically recovered from its defocused microscopic transmission images, applying 1D transport-of-intensity equation and inversed Abel transform. The index profile features positive axial Δn, enveloped by a negative zone. Such a shape of the profile suggests the axial densification of the material, while the tensile stress generates the enveloping area of decreased index.

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Femtosecond laser-induced periodic surface structures: importance of transient excitation stages

Paper 8077-8 of Conference 8077
Date: Monday, 18 April 2011
Time: 11:30 – 11:55

Author(s): Jörn Bonse, Jörg Krüger, Bundesanstalt für Materialforschung und -prüfung (Germany); Marcus Rohloff, Susanta K. Das, Sandra Höhm, Arkadi Rosenfeld, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany)

The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of metals, semiconductors and dielectrics by linearly polarized high-intensity Ti:sapphire fs-laser pulses (pulse duration ~130 fs, center wavelength ~800 nm) is studied experimentally and theoretically. In the experiments, two different types of LIPSS exhibiting very different spatial periods are observed (so-called LSFL - low spatial frequency LIPSS, and HSFL - high spatial frequency LIPSS), both having a different dependence on the incident laser fluence and pulse number per spot. The experimental results are analyzed by means of a new theoretical approach, which combines the generally accepted LIPSS theory of J.E. Sipe and co-workers with a Drude model, in order to account for transient changes of the optical properties of the irradiated materials. The joint Sipe-Drude model is capable of explaining numerous aspects of fs-LIPSS formation, i.e., the orientation of the LIPSS, their fluence dependence as well as their spatial periods. The latter aspect is specifically demonstrated for crystalline silicon, which show experimental LSFL periods somewhat smaller than the laser wavelength. This behaviour is caused by the excitation of surface plasmon polaritons, and the subsequent interference between its electrical fields with that of the incident laser beam, resulting in a spatially modulated energy deposition at the surface. In dielectric materials, experiments with double-fs-laser-pulse irradiation sequences of variable temporal pulse-to-pulse separation further confirm the importance of the transient excitation stages during the early stages of LIPSS formation.

Large aperture Nd:glass amplifiers with high-pulse repetition rate

Paper 8080B-37 of Conference 8080B
Date: Monday, 18 April 2011
Time: 14:00 – 14:20

Author(s): Alexey A. Kuzmin, Andrey A. Shaykin, Efim A. Khazanov, Institute of Applied Physics (Russian Federation)

Recently an interest in nanosecond Nd:glass lasers has increased all over the world. Such lasers are widely used for experiments on laser thermonuclear synthesis and in other fundamental and applied researches. One of the examples is ELI. Nd:glass is indispensable for creation of powerful femtosecond laser setups of petawatt level. In all types of petawatt lasers and projects energy is initially reserved in a nanosecond pulse of Nd:glass laser. Limitations on pulse repetition rate are thermal effects in Nd:glass caused by low heat conductivity and large aperture of glass amplifiers. A basic restriction is glass fracture when the thermally induced pressure threshold is exceeded. In practice, however, lasers work with smaller repetition rates because of accumulation of radiation depolarization and strong aberrational thermal lens. All these effects reduce the quality of laser radiation. The results of studies of thermally induced depolarization and thermal lens in large aperture Nd:glass rod amplifiers (100, 85, 60 and 45 mm in diameter) are reported in this paper. These amplifiers are used in a petawatt parametrical laser system PEARL (IAP RAS, Nizhny Novgorod, Russia). Our investigation will allow us significantly decrease the pulse repetition period from 30 to 3 minutes. Also it is shown the possibility of creation of a 200 J 20 ns Nd:glass laser with a pulse repetition period about a minute. The radiation of this laser can be used as a pump for a Ti:Sa crystal. It allows generating sub-petawatt pulses with high repetition rate.

Holographic recording diffraction gratings in BB-640 photographic emulsions with femtosecond pulses in infrared region

Paper 8074-12 of Conference 8074
Date: Tuesday, 19 April 2011
Time: 8:40 – 9:10

Author(s): Antonio Fimia, Pablo Acebal, Salvador Blaya, Luis Carretero, Roque Fernando Madrigal, Angel Murciano, Jose Neftalí, Univ. Miguel Hernández de Elche (Spain)

In this paper we show the experimental response of BB-640 photographic emulsion to the interference of two infrared femtosecond pulses. We have analyzed the influence of bleaching process and the thickness of the emulsions, considering shrinkage effects and sensitivity of photographic materials. The experimental setup consists of an afocal system composed of two plano-convex lenses of focal length of 100 mm and numerical aperture of 0.22, with a distance between them set to be equal in order to have a 4f system. A beamsplitter is a diffraction grating that is placed at the front focal plane of the first lens. The gratings are recorded by the interference of two gaussian beams from a femtosecond pulse laser mode sapphire laser. The pulse width is 120 fs and 76 Mhz of repetition frequency. At the interference planes the intensity is 340 mW and the area is 950 micron of diameter. In this conditions we have 0.47 MW/cm2 of pulse intensity. Due to the BB-640 photographic plate is red sensitive but with an absorption at 790 nm lower than 1%, and the grain size is 18-20nm, so the sensitivity is very low, so the exposure time need to record the gratings is from 1s to 96s. As a result we have experimentally demonstrated that transmission holographic gratings can be recorded in BB-640 emulsion with femtosecond laser in near infrared region with diffraction efficiency up to 30%, the thickness of the photographic emulsions and the bleached process has been analyzed and the sensitivity has been optimized with D8 developer

Electron kinetics in semiconductors and metals irradiated with VUV-XUV femtosecond laser pulses

Paper 8077-27 of Conference 8077
Date: Tuesday, 19 April 2011
Time: 14:20 – 14:45

Author(s): Nikita A. Medvedev, Baerbel Rethfeld, Technische Univ. Kaiserslautern (Germany)

When ultrashort laser pulses irradiate a solid, photoabsorption by electrons in conduction or valence band (as well as by ionization of deep atomic shells) produces nonequilibrium highly energetic free electrons gas. We study the ionization and excitation of the electronic subsystem in a semiconductor and a metal (solid silicon and aluminum, respectively). The irradiating femtosecond laser pulse has a duration of ~10 fs, and a photon energy of few tens of femtoseconds. The classical Monte Carlo method is extended to take into account the electronic band structure and Pauli's principle for excited electrons. In the case of semiconductors this applies to the holes as well. Conduction band electrons and valence band holes induce secondary excitation and ionization processes. We discuss the transient electron dynamics with respect to the differences between semiconductors and metals. For the case of semiconductors it is split into two parts by the band gap. For metals, the electronic distribution is split up into two different branches: a low energy distribution as a slightly distorted Fermi-distribution and a long high energy tail. We compare the calculated electron distributions with the spectroscopy data obtained in recent experiments with the FLASH laser in DESY, Hamburg. We also calculate a lattice heating by electrons irradiated with photons of different energies. The results suggest that the lattice dynamics is affected by the initial nonequilibrium electronic state.

Deep UV generation and fs pulses characterization using strontium tetraborate

Paper 8071-19 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 16:20 – 16:40

Author(s): Aleksandr S. Aleksandrovsky, Kirensky Institute of Physics (Russian Federation); Andrey M. Vyunishev, Siberian Federal Univ. (Russian Federation); Aleksandre I. Zaitsev, Kirensky Institute of Physics (Russian Federation); Anton A. Ikonnikov, Gennadiy I. Pospelov, Vladimir E. Rovsky, Vitaliy Slabko, Anastasiya A. Zhokhova, Siberian Federal Univ. (Russian Federation)

Strontium tetraborate (SBO) is attractive for nonlinear optics due to its transparency window that allows nonlinear optical conversion to the wavelengths down to 125 nm. It possesses largest nonlinearity among crystals transparent below 270 nm. Angular phase matching and standard QPM in SBO are absent. Phase matching is, however, possible due to random QPM using one-dimensional nonlinear photonic crystal (NPC) structures. These NPC are of growth origin and cannot be formed in desired geometry, but their properties depend on the growth process. Different types of NPC possess different nonlinear properties and must exhibit different spectral dependence of frequency conversion efficiency. These spectral dependences for NPC SBO typically protrude from near IR to near UV in the fundamental wave scale. Various NPC structures are described, and their calculated spectral dependences are compared. Experimental study of these structures is reported for the process of doubling of the second harmonic of fs Ti:S laser. Tuning of generated radiation is obtained in the range 187.5 - 232.5 nm, with extreme insensitivity to the angular orientation of NPC. Behaviour of tuning curve along investigated fundamental wave range is similar in all studied samples. Conversion efficiency and spectral quality of generated radiation is experimentally shown to grow better when using NPC with improved structure. Prospects of VUV converter on a single NPC are discussed. The concept of NPC band structure is discussed, and experimental proof for red rotational shift of NPC band structure is presented, in contrast to blue rotational shift of the linear PC band structure.

Damage of amorphous carbon induced by x-ray femtosecond free electron lasers pulses

Paper 8077-35 of Conference 8077
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Shafagh Dastjani Farahani, European XFEL GmbH (Germany)

Free-electron lasers (FEL) deliver femtosecond millijoule light pulses in the soft to hard x-ray photon energy range. The interaction of such light pulses with x-ray mirror coating is a very important issue for the efficient operation of these facilities. Hence, understanding the interaction mechanisms occurring at the surface of the optical elements is a critical factor. We investigate the damage caused by an FEL pulse on x-ray mirror coatings. The interesting candidate for this purpose is amorphous Carbon (a-C). We will present results of damage studies performed at two different Free-Electron Laser facilities: FLASH in Hamburg and LCLS in Stanford. The experiments at FLASH were performed with two different photon energies (91 eV and 177 eV) and under different geometrical conditions: normal and grazing incidence, above and below the critical angle. Amorphous-Carbon samples with 40 and 900 nm thickness coated on silicon (Si) substrate were used. The damage fluence threshold corresponding to each experimental condition was determined, in particular the damage fluence threshold of a 40 nm a-C sample under 4.3 ° grazing incidence angle at 177 eV photon energy was found out to be 43.7mJ/cm2. The experiments at LCLS were performed at 830 eV photon energy and normal incidence angle. For the 1400 nm thick a-C sample, a fluence threshold of 0.27 J/cm² was determined. To grasp a better understanding of the structural changes, the damage spots were investigated by Atomic Force Microscopy and Micro Raman Spectroscopy. The corresponding results indicate that the irradiated a-C undergo a phase transition leading to formation of nanocrystallites of graphite.

Electron kinetics in liquid water excited with a femtosecond VUV laser pulse

Paper 8077-43 of Conference 8077
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Klaus Huthmacher, Bärbel Rethfeld, Nikita Medvedev, Technische Univ. Kaiserslautern (Germany)

We describe theoretically the interaction of an ultrashort VUV-XUV laser pulse (10fs, photon energy of 50eV) with liquid water. Incident photons ionize water molecules and create free electrons. These excited electrons interact via elastic collisions with other water molecules and produce secondary electrons due to ionization. To track each free electron and its collisions event by event, we use the Monte Carlo method similar to [1], which we extended to take into account the electron transport. This approach allows us to describe a transient non-equilibrium behaviour of irradiated water at femtosecond timescales. As results we present the transient electron- and energy- distributions as a function of depth. Furthermore, we exhibit a time resolved description of the total amount of electrons and we also show the corresponding energy redistribution: change in the kinetic energy of excited electrons, increase of the energy of holes, and energizing of water molecules via elastic collisions. [1] N. Medvedev and B. Rethfeld New Journal of Physics 12 (2010) 073037

Multi-threaded parallel simulation of non-local non-linear problems in ultrashort laser pulse propagation in the presence of plasma

Paper 8071-41 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Mandana Baregheh, Aston Univ. (United Kingdom); Holger Schmitz, Imperial College London (United Kingdom); Vladimir K. Mezentsev, Aston Univ. (United Kingdom)

We describe a parallel multi-threaded approach for high performance modelling of wide class of phenomena in ultrafast non-linear optics. Non-linear wave equation in the form of the Generalised Non-Linear Schroedinger Equation (GNLSE) is a generic mathematical model describing narrow bandwidth wave propagation in envelope approximation. In this paper we consider a parallel numerical solution for a specific model which describes femtosecond laser pulse propagation in transparent media. In this case GNLSE is coupled to Drude model of plasma resulting from multi-photon and avalanche ionisation processes. However our approach can be extended to similar models. We compare performance of the multithreaded parallel code implemented for Nvidia Graphics Processing Units using CUDA programming interface with a serial CPU version. Coupling between the equations makes GNLSE non-local which results in impossible straightforward parallel implementation. To simplify the problem, the splitting operator method is used to reduce GNLSE it into a succession of linear and non-linear steps. The linear term is solved in frequency domain using CUDA's multi-threaded version of the Fast Fourier Transform. The parallel simulation of the non-linear term is not straightforward due to non-locality induced by coupling between plasma and electromagnetic wave. We develop the parallel numerical solution of non-linear step by expressing the non-linear problem as an integral equation in time domain. We have managed to successfully parallelise solution of GNLSE non-locally coupled with plasma using CUDA interface. We have tested the accuracy of the results and found satisfactory linear scaling up with 10x to 30x factor of speedup on Nvidia Tesla C1060 compared to CPU implementation.

Partial-coherence colored-noise approach to model FEL pulse statistics

Paper 8078-35 of Conference 8078
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Thomas Pfeifer, Yuhai Jiang, Max-Planck-Institut für Kernphysik (Germany); Stefan Duesterer, Deutsches Elektronen-Synchrotron (Germany); Robert Moshammer, Joachim Ullrich, Max-Planck-Institut für Kernphysik (Germany)

A convenient model was developed to describe the electric fields produced by free-electron laser pulses (FELs). In the self-amplified spontaneous emission (SASE) mode, these fields vary significantly on a shot-to-shot basis. Our method allows to generate sets of pulse shapes that statistically match experimentally accessible information: the single-shot and average spectral shape, and the average pulse duration. As will be shown, this statistical information on the FEL pulse shape is important to obtain agreement between experimental and theoretical data on strong-field FEL-matter interaction. In addition, it will become clear how statistically fluctuating FEL fields of a given average pulse duration allow for a better temporal resolution than attainable with bandwidth-limited shot-to-shot reproducible fields of the same duration.

Pilot experiment on ion acceleration and diagnostics at the new femtosecond laser system at PALS

Paper 8079A-61 of Conference 8079A
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Jan Prokupek, Daniele Margarone, Jan Hrebicek, Miroslav Krus, Andriy Velyhan, Institute of Physics of the ASCR, v.v.i. (Czech Republic); Miroslav Pfeifer, Josef Krasa, Institute of Physics (Czech Republic); Tomáš Mocek, Bedrich Rus, Institute of Physics of the ASCR, v.v.i. (Czech Republic)

An experimental campaign on laser-driven ion acceleration by using the 20 TW, Ti:Sapphire laser system recently installed at PALS facility, was performed. The experiment was mainly aimed to proof that a time-of-flight (TOF) based diagnostics is capable of characterizing light, fast ion beams (mainly protons) accelerated by fs-class lasers. The standard TNSA (target normal sheath acceleration) scheme was used with various thin plastic and metallic targets (1÷10m) in order to optimize both the fast proton beam maximum energy and total charge. The main diagnostics used along the experiment were: i) Faraday cups with various geometries, placed at short and long distances from the irradiated target, giving an absolute estimation of the total ion beam charge; ii) silicon carbide (SiC) semiconductor detectors showing a very high sensitivity in the detection of high energy particles. A filtering technique was used in order to cutoff the X-ray/UV plasma radiation hitting the detector surface, as well as to stop the slow plasma particles. The complementary information provided by the employed diagnostics showed a maximum proton energy approaching 1 MeV with a total charge strongly depending on the target thickness and material.

Determination of temporal FEL pulse properties: challenging concepts and experiments

Paper 8078-16 of Conference 8078
Date: Thursday, 21 April 2011
Time: 8:30 – 9:00

Author(s): Stefan Duesterer, Deutsches Elektronen-Synchrotron (Germany)

One of the most challenging tasks for the FEL photon diagnostics is the precise determination of the FEL pulse duration or even getting information on the substructure of the SASE pulses. The knowledge of the temporal pulse characteristics is not only important for nonlinear interactions which rely purely on the correct determination of the intensity, but also to gain insight on the dynamics of the investigated processes. Here, the resolution of pump-probe experiments relies heavily on knowledge of the pulse duration for one color pump-probe and in addition on the precise arival time difference for 2-color pump probe experiments. Due to the wide range of available parameters at the existing and planed - photon energies ranging from VUV to X-rays with pulse durations of few fs or even sub fs range up to pulses with several 100 fs pulse duration - a variety of methodes has to be investigated and utilized in order to characterize the temporal structure of these pulses. Moreover due to the statistical nature of the SASE process the pulse shape (consisting of few up to hundreds of sub pulses) varies pulse by pulse. Here, techniques to characterize the pulse shot by shot - increasing the level of complexity in contrast to averaging techniqhes by far - are needed. The talk will provide an overview of various concepts how to measure the pulse duration for VUV to X-rays focussing on the range of application, the strength and weaknesses for the different approaches. Finaly, results of several experimental campaigns characterizing the temporal shape of the FEL pulses at FLASH and LCLS will be presented.

Study of acousto-optic programmable dispersive filter for amplitude and phase control of femtosecond seed pulse in sub PW OPCPA laser system

Paper 8080B-38 of Conference 8080B
Date: Monday, 18 April 2011
Time: 14:20 – 14:40

Author(s): Vladislav Ginzburg, Eugeny Katin, Efim Khazanov, Vladimir Lozhkarev, Mikhail Martyanov, Ivan Yakovlev, Institute of Applied Physics (Russian Federation); Sergey Chizhikov, Vladimir Molchanov, Nikolay Solodovnikov, Moscow State Institute of Steel and Alloys Technological Univ. (Russian Federation); Yuriy Kitaev, Voronezh State Univ. (Russian Federation)

The quality of compressed pulse in high peak power laser systems based on chirped pulse amplification is determined by non compensated high order dispersion and gain bandwidth narrowing in amplifiers. Programmable device modifying spectral amplitude and phase of seed femtosecond pulse can be used for improving duration and contrast of compressed pulse and increasing amplification efficiency. Proposed by P. Tournois acousto-optic programmable dispersive filter (AOPDF) seems to be the most suitable for this purpose. We designed and implemented an original AOPDF and tested it in front-end system of sub PW OPCPA laser. AOPDF cell was placed between femtosecond oscillator and stretcher. The diffracted output beam has no deflection from initial direction, this fact allowed to implement AOPDF in existing lasers easily. The filter operated with central wavelength of 1250nm with bandwidth of 120nm. Maximal programmable delay was 15ps. Usage of acousto-optic paratellurite single crystal with length of 53mm allowed reaching diffraction efficiency of 70%. The AOPDF has demonstrated high spectral resolution (~1nm) and acceptable contrast (not worse than 1:100). Proper shaping of transforming function allowed enlarging amplified signal spectrum bandwidth in twice. Applying of additional dispersion to the phase of injected femtosecond pulse provided corresponding changes in the measured autocorrelation function of compressed pulse. Those changes were in good agreement with results of numerical simulation. AOPDF cell demonstrated high efficiency, flexibility of seed pulse control and simplicity of operation. It opens way for achievement signal radiation with power more than 1PW by increasing of parametric efficiency and shortening pulse duration dew to compensation of stretcher-compressor dispersion.

Coherent transition radiation generated by a femtosecond electron beam from an optically injected laser-plasma accelerator

Paper 8079A-14 of Conference 8079A
Date: Tuesday, 19 April 2011
Time: 8:30 – 9:00

Author(s): Olle Lundh, Lund Univ. (Sweden); Jerome Faure, Jaeku Lim, Clement Rechatin, Victor Malka, Ecole Nationale Supérieure de Techniques Avancées (France); Erik Lefebvre, Commissariat à l'Énergie Atomique (France)

Laser-plasma accelerators, driven by ultraintense and ultrashort laser pulses, sustain accelerating gradients of several hundred giga-volts-per-metre and can deliver high quality electron beams with low energy spread, low emittance and up to giga-electron-volt peak energy. The use of two colliding pulses in a collinear geometry can produce a stable source of electrons that is easily tunable in energy. Here, we report on results of recent experiments with two laser beams colliding with an angle of 135°, thus having the advantage of protecting the laser system from any feedback and facilitating immediate access to the electron beam. For temporal characterization of the electron beam, we measure coherent optical transition radiation in a wide spectral band. Measurements of the absolute number of photons in the mid-infrared spectral band indicate that the electron bunches have durations of only a few femtoseconds. The shape and absolute intensity of the measured CTR spectrum agrees with analytical modeling of electron bunches with durations of 3 to 5 fs [full width at half maximum (fwhm)] and peak currents of 3 to 4 kA, depending on the bunch shape. Under certain conditions, we observe strong oscillations in the visible part of the CTR spectrum. A detailed Fourier analysis reveals that these spectral modulations result from interference of radiation produced by multiple electron bunches. The bunch separation is related to the fringe separation and shifts with plasma density but is always an integer number of plasma wavelengths. It is found that electrons are injected in single- and multiple buckets up to at least ten plasma wave periods behind the first electron bunch.

Up- and down-conversion at three-waves interaction in medium with combined nonlinear response

Paper 8071-5 of Conference 8071
Date: Tuesday, 19 April 2011
Time: 15:50 – 16:10

Author(s): Vyacheslav A. Trofimov, Vladislav V. Trofimov, Lomonosov Moscow State Univ. (Russian Federation)

We investigate an efficiency of SFG and DFG of femtosecond pulse in medium with quadratic and cubic responces of medium simultaneously. This analysis is made on the base of obtained explicit solution of set of Schrodinger equations in the frame-work of long pulse approximation both for the case of phase-matching and phase mismatching of interacting waves. Using the found explicit solution of Schrodinger equations, we make full analysis of number of solutions. We have shown the bistable regime of frequency conversion. The efficiency of SFG and DFG process strongly depends on phase mismatching, on ratio of intensities of interacting waves and on intensities of optical pulses. Our analysis is proved by computer simulation made on the base of set of nonlinear Schrodinger equations. It should be stressed that considered process is widely used for trebling of frequency of laser pulse. First stage is a doubling of optical frequency. Then, the second stage is a mixing of pulses with fundamental and doubling frequencies. As a consequence, a generation of laser pulse with summary frequency is obtained. The other application of considered problem is a genration of wave with THz frequence at mixing of high intensive femtosecond pulses in medium with quadratic nonlinear response. As it is well-known for such conditions of interaction of laser pulses it is necessary to take into account the action of cubic nonlinear response also.

Optimization and characterization of a femtosecond tunable light source based on the soliton self-frequency shift in photonic crystal fiber

Paper 8071-17 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 15:10 – 15:30

Author(s): Charles-Henri Hage, Bertrand Kibler, Univ. de Bourgogne (France); Eric Mottay, Amplitude Systemes (France); Hervé Rigneault, Institut Fresnel (France); John M. Dudley, Univ. de Franche-Comté (France); Guy Millot, Christophe Finot, Univ. de Bourgogne (France)

We report here an extensive experimental study dealing with the optimization and the full characterization of a photonic crystal fiber (PCF)-based light source for generating femtosecond tunable pulses that are suitable for coherent anti-Stokes Raman scattering microscopy. Starting from a commercial oscillator which delivers 20 nJ/ 190 fs Gaussian pulses at 1033 nm, we have taken advantage of the process of soliton-self frequency shift (SSFS) induced by Raman scattering. As a first optimization step, we have experimentally tested the performance of three commercially available PCFs exhibiting distinct group velocity dispersion (GVD) characteristics. The spectral profile of GVD highly impacts the SSFS process. The Power Spectral Density (PSD) is directly proportional to the ratio of the GVD over the nonlinearity. Using high dispersion value at the pump wavelength, we have achieved a 300 µW/nm PSD with a 30% conversion efficiency from the pump to the shifted soliton. Regarding the spectral shift, a maximum frequency shift of 340nm has been achieved and a close to linear dependence of the frequency shift versus the initial power has been recorded. Autocorrelation measurements have confirmed that the output pulses are nearly transform limited with a duration of 100-fs. Additional measurements based on radio-frequency spectrum analysis were finally carryed out to estimate the level of amplitude and timing jitters of the output pulses. 0.15% intensity noise and 300-fs timing jitter for any wavelength shifts of the femtosecond soliton pulse have been demonstrated, those values being quite similar to the jitters of the initial oscillator.

Observation of long range coherent OTR from LPA electron beams

Paper 8079A-16 of Conference 8079A
Date: Tuesday, 19 April 2011
Time: 9:20 – 9:40

Author(s): Chen Lin, Kei Nakamura, Jeroen van Tilborg, Anthony J. Gonsalves, Nicholas H. Matlis, Thomas Sokollik, Satomi Shiraishi, Jens Osterhoff, Carl B. Schroeder, Carlo Benedetti, Eric Esarey, Wim P. Leemans, Lawrence Berkeley National Lab. (United States)

We report the observation of coherent optical transition radiation (COTR) from electron bunches that have propagated for up to 4 m from the exit the laser plasma accelerator (LPA) inside a vacuum tube. Transition radiation images and their spectra, produced by electrons passing through two separate foils (located from the LPA at 2.3 m and 3.8 m) were recorded with a high resolution imaging system and spectrometer, respectively. Transition radiation in the visible wavelength regime was measured that had signal levels that are more than two orders of magnitude greater than expected from incoherent emission, indicating that femtosecond structure on the electron beams persists over multi-meter scale propagation distances. The persistence of femtosecond timescale structure on the bunches after multi-meter propagation, implies an upper limit for energy spread and emittance. Different coherent enhancement between the two stations has also been observed, consistent with dynamic changes of the bunch structure due to beam velocity bunching. Work supported by US DOE Contract No. DE-AC02-05CH11231.

Coherent transition radiation as a tool for investigating bunches of electrons produced by laser wakefield accelerators

Paper 8075-21 of Conference 8075
Date: Thursday, 21 April 2011
Time: 9:40 – 10:00

Author(s): Constantin Aniculaesei, Gregor Welsh, Riju Issac, Enrico Brunetti, Richard P. Shanks, Silvia Cipiccia, Maria P. Anania, Bernhard Ersfeld, Samuel M. Wiggins, Dino A. Jaroszynski, Univ. of Strathclyde (United Kingdom)

The laser plasma wakefield accelerator can produce electron bunch that are 1-5 femtosecond in duration. These extremely short durations preclude using conventional methods such as electro-optic crystals or streak cameras to measure their lengths. However, coherent transition radiation emitted when charged particles cross the boundary between two different dielectric media, can be used to accurately determine the electron bunches parameters. We will show how an interference pattern in transition can be used to extract relevant parameters of the electron bunch, such as emittance, bunch duration and energy.

Tunable two-stage laser-plasma accelerator based on longitudinal density tailoring

Paper 8079A-1 of Conference 8079A
Date: Monday, 18 April 2011
Time: 8:40 – 9:10

Author(s): Anthony J. Gonsalves, Kei Nakamura, Chen Lin, Dmitriy Panasenko, Satomi Shiraishi, Thomas Sokollik, Carlo Benedetti, Carl B. Schroeder, Cameron G. R. Geddes, Jeroen van Tilborg, Eric Esarey, Csaba Toth, Wim P. Leemans, Lawrence Berkeley National Lab. (United States)

The high acceleration gradient in laser-driven plasma accelerators (LPAs) has allowed for the production of compact devices delivering high-quality electron beams with GeV energies from acceleration over centimeter length scales. LPAs have been considered for driving modules of future high energy colliders, and hyper-spectral light sources capable of delivering intrinsically synchronized femtosecond beams of electrons and light pulses, with frequency ranging from THz to gamma ray. These applications require a high degree of stability, beam quality, and tunability. Similar to the implementation of conventional accelerators, here we report on the generation of such beams from a laser plasma accelerator using separate injection and acceleration modules. This two-stage approach relies on a longitudinally tailored plasma density profile and has allowed for the generation of stable beams with energies tunable in the range of 100 to 400 MeV. Work supported by US DOE Contract No. DE-AC02-05CH11231.

Development of a 10 mJ-level optically synchronized picosecond Yb:KYW amplifier at 1040 nm for OPCPA pumping

Paper 8080A-7 of Conference 8080A
Date: Monday, 18 April 2011
Time: 11:30 – 11:50

Author(s): Celso P. João, Instituto de Plasmas e Fusão Nuclear, Associação EURATOM/IST (Portugal); Jörg Körner, Martin Kahle, Hartmut Liebetrau, Ruediger Seifert, Mathias Lenski, S. Pastrik, Joachim Hein, Thomas Gottschall, Jens Limpert, Friedrich-Schiller-Univ. Jena (Germany); Vincent Bagnoud, Gesellschaft für Schwerionenforschung GmbH (Germany)

We report the results on a novel 10 mJ-level diode-pump Yb:KYW amplifier at 1040 nm. This amplifier operates in the picosecond regime with a repetition rate of 10 Hz. It will be used in the front end of a petawatt laser system for pumping an optical parametric chirped pulse amplifier (OPCPA) for contrast enhancement. For the synchronization purpose the amplifier is seeded by pulses that are derived from the femtosecond oscillator of the petawatt laser system. After amplification in a double stage fiber amplifier the pulses are injected into the Yb:KYW regenerative cavity. Finally, the pulses are compressed to 1 ps before second harmonic conversion in order to achieve a high contrast with the parametric amplification sage. This work was partially supported by Fundação para a Ciência e a Tecnologia (grants PTDC/FIS/71101/2006 and SFRH/BD/68865/2010), LASERLAB-Europe (EC's FP7, grant agreement no. 228334), and Association EURATOM/IST.

Saturation of Ce:YAG scintillator exposed to ultrashort VUV, XUV and hard X-ray radiation pulses

Paper 8077-32 of Conference 8077
Date: Tuesday, 19 April 2011
Time: 16:50 – 17:15

Author(s): Jacek Krzywinski, SLAC National Accelerator Lab. (United States); Andrzej Andrejczuk, Univ. of Bialystok (Poland); Richard M. Bionta, Lawrence Livermore National Lab. (United States); Jaromir Chalupský, Jaroslav Cihelka, Libor Juha, Institute of Physics of the ASCR, v.v.i. (Czech Republic); Marco Kirm, Univ. of Tartu (Estonia); Marek Jurek, Ryszard Sobierajski, Institute of Physics (Poland); Kai Tiedtke, Deutsches Elektronen-Synchrotron (Germany)

We report on investigation of saturation phenomena of the Ce:YAG scintillator crystal under influence of intense, femtosecond VUV, XUV and hard X-ray radiation pulses. The study was performed at the DESY and SLAC FEL sources delivering photons at 90 nm, 13.5 nm and 0.15 nm wavelength. The saturation of the photon yield occurs at the energy deposition level of 25±15 J/cm3 into the crystal in the photon energy range 10 eV - 8300 eV. This is consistent with earlier findings [1] that the internal radiance efficiency ksi does not depend strongly on the energy of incident photons ksi=0.035 +/- 0.015 in the range 10eV - 100000 eV. The results obtained in this report can be applied in prediction of saturation effects for imaging diagnostics of bright photon and particle beams provided by novel accelerators. The discussion of possible saturation mechanisms follows. [1] I. Kandarakis et al., Nucl. Instr. and Meth. A 538, 615 (2005)

Lifetime and damage threshold properties of reflective x-ray coatings for the LCLS free electron laser

Paper 8077-1 of Conference 8077
Date: Monday, 18 April 2011
Time: 8:30 – 8:55

Author(s): Regina Soufli, Lawrence Livermore National Lab. (United States); Mónica Fernández-Perea, Lawrence Livermore National Lab. (United States) and Consejo Superior de Investigaciones Científicas (Spain); Stefan P. Hau-Riege, Sherry L. Baker, Jeff C. Robinson, Eric M. Gullikson, Lawrence Livermore National Lab. (United States); John D. Bozek, Nicholas M. Kelez, Sebastien Boutet, SLAC National Accelerator Lab. (United States)

The Linac Coherent Light Source (LCLS) x-ray free electron laser (FEL) has been operational since 2009 at the SLAC National Accelerator Laboratory in California. This first-of-a-kind x-ray source produces ~100 femtosecond monochromatic x-ray pulses of unprecedented brightness (about 10 orders of magnitude higher than current 3rd generation synchrotron sources) in the first harmonic ranging between 0.8 and 8 keV. The revolutionary capabilities of the LCLS will generate a wealth of new research in the fields of physics, biology and materials science. The uniquely high instantaneous dose of the LCLS beam led to x-ray mirror designs consisting of an especially modified reflective coating (boron carbide or silicon carbide) deposited on a silicon substrate. Furthermore, the coherence preservation requirements for these mirrors result in very stringent surface figure and finish specifications. We have demonstrated working LCLS x-ray mirrors with coating thickness errors < 0.35 nm rms and overall figure errors ~ 2.5 nm rms across 385-mm-long clear apertures after mounting and installation were completed. Some of the LCLS mirrors start showing signs of degradation exhibited as carbon-based deposits on top of the coating surface. The main challenge in removing such contamination and restoring the mirror performance is that carbon is the main constituent of both the contaminated regions and the carbide coatings. Experimental results from techniques aiming in extending the lifetime of the LCLS x-ray mirrors will be discussed. Experimentally determined damage thresholds for the LCLS reflective coatings will also be presented and compared with theoretical models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Work was supported in part by DOE Contract DE-AC02-76SF00515. This work was performed in support of the LCLS project at SLAC.

Soft x-ray laser driven ion acceleration and ablation in solids: niobium, vanadium and their deuterides

Paper 8077-4 of Conference 8077
Date: Monday, 18 April 2011
Time: 9:40 – 10:00

Author(s): Bianca S. Iwan, Jakob Andreasson, Uppsala Univ. (Sweden); Andrzej Andrejczuk, Univ. of Bialystok (Poland); Elsa Abreu, Uppsala Univ. (Sweden); Magnus Bergh, Swedish Defence Research Agency (Sweden); Carl Caleman, Technische Univ. München (Germany); Art J. Nelson, Lawrence Livermore National Lab. (United States); Saša Bajt, Deutsches Elektronen-Synchrotron (Germany); Jaromir Chalupský, Institute of Physics of the ASCR, v.v.i. (Czech Republic); Henry N. Chapman, Roland R. Fäustlin, Deutsches Elektronen-Synchrotron (Germany); Vera Hajkova, Institute of Physics of the ASCR, v.v.i. (Czech Republic); Philip A. Heimann, Lawrence Berkeley National Lab. (United States); Björgvin Hjörvarsson, Uppsala Univ. (Sweden); Libor Juha, Institute of Physics of the ASCR, v.v.i. (Czech Republic); Dorota Klinger, Institute of Physics (Poland); Jacek Krzywinski, SLAC National Accelerator Lab. (United States); Bob Nagler, Univ. of Oxford (United Kingdom); Gunnar K. Palsson, Uppsala Univ. (Sweden); Waldemar Singer, Deutsches Elektronen-Synchrotron (Germany); Marvin M. Seibert, Uppsala Univ. (Sweden); Ryszard Sobierajski, Institute of Physics (Poland) and FOM-Institute for Plasma Physics (Netherlands); Sven Toleikis, Thomas Tschentscher, Deutsches Elektronen-Synchrotron (Germany); Sam M. Vinko, Univ. of Oxford (United Kingdom); Richard W. Lee, Lawrence Livermore National Lab. (United States); Janos Hajdu, Nicusor Timneanu, Uppsala Univ. (Sweden)

Extremely intense and ultra-short soft X-ray pulses from the FLASH Free-electron Laser in Hamburg were focused to produce sufficiently high energy densities to study materials under extreme conditions (MEC). These conditions are the focus of interest for a wide range of disciplines, from structural biology to fusion, as any sample subjected to a tightly focused FLASH pulse will rapidly turn into plasma. Here we describe results with a new sub-micron focusing optic, where power densities exceeding 10^17 W/cm^2 could be reached with 20 fs soft X-ray pulses. We report the interaction of such pulses with solids, including niobium, vanadium and their deuterides. The interaction was characterized by time-of-flight ion spectrometry and by an off-line analysis of the ensuing craters on the sample surfaces. The results were modelled, using a non-local thermodynamic equilibrium code with radiation transfer, complemented with a self-similar isothermal fluid model for plasma expansion into vacuum. The results show saturation in the ablation process at power densities exceeding 10^16 W/cm^2. This effect can be linked to a transiently-induced X-ray transparency in the solid by the femtosecond X-ray pulse at high power densities. Furthermore, protons and deuterons with kinetic energies of several keV have been measured, and these concur with predictions from plasma expansion models. Our results show a clear correlation between the energy density on the sample surface and the number and energy of ions ejected during crater formation. The correlation can be used to find the focus, which is not a trivial task by conventional methods when using sub-micron focusing. Combined with the information about beam intensity, an ion time-of-flight spectrometer provides sensitive indication about the power density on the sample.

Transient analysis of thermal distorsion in a silicon substrate on incidence of a single soft X-ray FEL pulse

Paper 8077-10 of Conference 8077
Date: Monday, 18 April 2011
Time: 13:25 – 13:50

Author(s): A. Rubens B. de Castro, Univ. Estadual de Campinas (Brazil) and Brazilian Synchrotron Source LNLS (Brazil); Aurea R. Vasconcellos, Roberto Luzzi, Univ. Estadual de Campinas (Brazil)

The analysis of thermal distortion in optical surfaces subjected to X-ray FEL pulses must address entirely new issues, as compared to the simpler case of synchrotron light produced in a storage ring. Our method starts from a formulation of non-equilibrium hydrodynamics, contemplating the energy and matter densities in the material medium, and its tensor fluxes of all orders. For times t>T0 (T0 estimated here as about 200 fsec) it is possible to truncate the infinite system of equations and solve them. T0 is a time after the optical excitation, such that for t>T0 local time-dependent functions quasi-temperature T(r,t) and density of matter n(r,t) can be defined. The solution of the resulting pair of equations then shows that, after incidence of a single typical soft X-ray FEL pulse, a silicon substrate will bulge locally at t about 200 nsec, creating a local surface figure error of circa 1 microrad. Its amplitude decays on a time scale of microseconds. If trains of femtosecond pulses spaced by a few hundred nanoseconds are contemplated, resonant enhancement of the surface bulge may increase the figure error to intolerable values. Current work is focused on extending the applicability of this non-equilibrium hydro-dynamic approach to times shorter than T0.

LASERIX: an open facility for developments of Soft X-ray and EUV lasers and applications

Paper 8080B-36 of Conference 8080B
Date: Monday, 18 April 2011
Time: 13:40 – 14:00

Author(s): David R. Ros, Univ. Paris-Sud 11 (France)

LASERIX is a high-power laser facility designed to produce High-repetition-rate XUV laser beams pumped by a Titanium:Sapphire la-ser. The objectives are to develop soft X-ray lasers (SXRL) at various wa-velengths and use them for applications. The facility is based on a tita-nium-doped sapphire (Ti:Sa), delivering pulse energy of 2 J at 10 Hz repetition rate at the exit of the front-end and 40 J before compression at 0.1 Hz repetition rate. The large width of the Ti:Sa spectrum opens the way to short pulses and to new SXRL schemes. Three different EUV and soft x-ray beam lines will run simultaneously: An EUV DGRIP/GRIP laser line at 10Hz, a femtosecond EUV high order harmonic laser line at 10Hz and a high energy soft x-ray laser line at 0.1Hz. This configuration highly enhances the scientific opportunities of the facil-ity. Indeed it will be possible to perform both Soft X-ray laser experiments and more generally pump/probe experiments, mixing IR and EUV sources. Then, this facility will be useful for the community, opening a large scale of Laser Interaction with Matter investigations. In this contribution, the main results concerning both the perspectives of the development of EUV and soft x-ray laser sources and their use for scientifical applications will be presented. Finally, we will indicate the perspectives of the LASERIX facility in the near future, especially taking into account the national (Institut de la Lu-mière Extrême: ILE project, laboratories working on the development of the XUV sources) and international (Extreme Light Infrastructure project) contexts.

The performance of a versatile setup for superconducting nanowire single photon detectors

Paper 8072A-3 of Conference 8072A
Date: Tuesday, 19 April 2011
Time: 9:30 – 9:50

Author(s): Mohsen Keshavarz Akhlaghi, Amir Hamed Majedi, Univ. of Waterloo (Canada)

We report on the performance of our new setup for testing Superconducting Nanowire Single Photon Detectors (SNSPDs). The optical cryostat consists of a dipstick that is firmly mounted on the edge of an optical table. It goes inside a liquid helium Dewar while not touching the body of the Dewar to achieve low-vibration operation with minimized cryogen consumption. A system of high vacuum chamber, radiation shields and cold widows is exploited to isolate the cold plate and SNSPD from unwanted heat loads and radiations. A temperature sensor, a heater, a capillary tube together with a roughing pump and a controller is used to adjust and monitor the operation temperature. A room temperature beam shaping and steering mechanism delivers the intensity and polarization controlled optical signals to the detector through free space optical access. The optical signals are generated by tuneable parametric down conversion of 1064nm femtosecond laser pulses in Periodically Poled Lithium Niobate. The electric response of the biased SNSPD after amplification stages can be monitored in real time on a fast oscilloscope or statistically on a programmable counter. We present our results on the performance of the various parts of the system. The achieved operation temperature range, its stability and also cryogen consumption rate is presented to elaborate the performance of the cryostat. We also present the results on the quantum efficiency and system quantum efficiency measurements in different operation temperatures and different excitation wavelengths. Furthermore, the dependency of the timing delay and timing jitter of the Niobium Nitride SNSPDs on biasing, operation temperature and excitation wavelengths are illustrated through a set of measured curves.

Modelling and design of high harmonic seeding in soft x-ray laser plasmas with both direct and stretched amplification techniques: application to ELI facilities

Paper 8080B-43 of Conference 8080B
Date: Tuesday, 19 April 2011
Time: 9:40 – 10:00

Author(s): Philippe Zeitoun, Ecole Nationale Supérieure de Techniques Avancées (France) and ENSTA-ParisTech (France) and ecole Polytechnique-ParisTech (France); Eduardo Oliva, Ecole Polytechnique (France); Marta Fajardo, Univ. Técnica de Lisboa (Portugal); Pedro Velarde, Univ. Politécnica de Madrid (Spain); David Ros, Univ. Paris-Sud 11 (France); Stéphane Sebban, Ecole Nationale Supérieure de Techniques Avancées (France)

Modelling and design of high harmonic seeding in soft x-ray laser plasmas with both direct and stretched amplification techniques. Application to ELI facilities. Philippe Zeitoun1, Eduardo Oliva1,2, Marta Fajardo3, Pedro Velarde1,2, D. Ros4, S. Sebban1 1- Laboratoire d'Optique Appliquée, France 2 - Instituto de Fusion Nuclear, Spain 3- Centro de Fisica dos Plasmas, Portugal 4- CLUPS, France Seeding soft x-ray laser by high harmonic beam demonstrated outstanding optical qualities [Zeitoun, 2004]. However, despite several attempts worldwide seeded soft x-ray lasers never succeeded in reaching energy per pulse higher than 1 µJ and even 90 nJ for solid amplifiers [2]. Based on 2D hydrodynamic and 3D ray-trace modelling we demonstrated that plasma tailoring opens up the way to achieve up to 40 µJ per pulse [Wang 2006]. In ASE mode, x-ray lasers pumped by long (400 ps) laser pulse demonstrated energy up to 12 mJ, but with very weak coherence and no polarisation[Rus, 2002]. Seeding such high-energy amplifier represents a very promising challenge [Ditmire, 1995]. Our Bloch-Maxwell model shown that seeding such amplifier with femtosecond HHG cannot extract more than 100 µJ. Therefore, we studied the seeding of stretched high harmonic leading to output energy up to 12 mJ in pulse that may be compressed down to 200 fs. We performed the full design of such soft x-ray amplification chain to be implemented on ELI, completed by possible timetable showing that seeded soft x-ray laser may deliver photons to users within few years followed by strong intensity raise with time culminating around 10^19 Wcm-2.

Tellurite suspended nanowire surrounded with large holes for single-mode SC and THG generations

Paper 8073B-103 of Conference 8073B
Date: Tuesday, 19 April 2011
Time: 9:50 – 10:10

Author(s): Meisong Liao, Guanshi Qin, Xin Yan, Chitrarekha Chaudhari, Takenobu Suzuki, Yasutake Ohishi, Toyota Technological Institute (Japan)

For a suspended nanowire, the holes surrounding the core are expected to be as large as possible to propagate the light at wavelengths as long as possible. However, the fabrication of nanowire surrounded with large holes is still a challenge so far. In this paper, a method which involves pumping positive pressure of nitrogen gas in both the cane fabrication and fiber-drawing processes, is proposed. A suspended nanowire, with a core diameter of 480 nm and an unprecedented large diameter ratio of holey region to core (DRHC) of at least 62, is fabricated in the length of several hundred meters. Owing to the large holes, the confinement loss of the suspended nanowire is insignificant when the wavelength of light propagated in it is 1700 nm. Additionally, the tube-shaped glass cladding of the suspended nanowire shifts the single-mode cutoff wavelength to 810 nm, which is much shorter than the cutoff wavelength, 1070 nm, of a naked nanowire with the same diameter. At the pump wavelength of 1064 nm the nanowire has an optimized nonlinear coefficient. A single-mode supercontinuum (SC) generation covering a wavelength range of 900-1600 nm is obtained under 1064 nm pump pulse with the peak power as low as 24 W. A single-mode third harmonic generation (THG) is observed by this nanowire under the pump of a 1557 nm femtosecond fiber laser. This work indicates that the suspended nanowire with large holes can provide high nonlinearity together with single-mode propagation, which leads to interesting applications in compact nonlinear devices.

Molecular dynamics simulations on time-dependent potential energy surfaces for the study of ultrafast phase transitions and coherent phonons

Paper 8077-26 of Conference 8077
Date: Tuesday, 19 April 2011
Time: 13:55 – 14:20

Author(s): Harald O. Jeschke, Johann Wolfgang Goethe-Univ. Frankfurt am Main (Germany)

Laser induced femtosecond structural changes in diamond, graphite, silicon and germanium are studied theoretically. In an attempt to treat both ionic motion and the changes in the electronic structure with sufficient accuracy, we employ molecular dynamics simulations on the basis of a time-dependent potential energy surface derived from a tight-binding Hamiltonian. The tight-binding description represents a compromise between computational efficiency and a sufficiently realistic treatment of the bonding and electronic structure in the materials. The shape and spectral composition of the laser pulse is explicitly taken into account. This approach is applied to the laser excitation of bulk diamond and allows a study of the conditions under which ultrafast graphitization takes place. A study of graphite in a slab geometry permits the investigation of a preablation mechanism: The deposited energy is not sufficient for ultrafast bond breaking, but the excitation of intense vibrational motion leads to repulsive interaction between the graphite layers. In the investigation of intense laser excitation of ultrathin silicon films, density modulations and thus the formation of large clusters is observed. By implementing a nonorthogonal tight binding scheme for germanium, we can address the softening of phonon modes in laser induced nonequilibrium. We determine the time scales of the structural response by following the attenuation of relevant Bragg peaks. Recent experiments are in good agreement with predictions from our theoretical approach.

Fast ions generation from nanostructure target irradiated by high intensity short laser pulse

Paper 8079A-24 of Conference 8079A
Date: Tuesday, 19 April 2011
Time: 14:20 – 14:40

Author(s): Alexander A. Andreev, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany)

One of the problems of laser particle acceleration physics is increasing of transformation of laser pulse energy into particle energy. Rather recently it was revealed that transformation of laser energy in ion energy increases at use a thin foils limited in size anywhere laser radiation absorption of such targets was not so high. In the present report it is offered to increase target absorption up to 95% and to optimize parameters of a relief and basic part of a target so that the additional absorbed energy is transferred mainly to the accelerated protons. The choice of optimum characteristics of a target is made by means of analytical and numerical modeling of a target set with characteristics near to optimum values. We investigated plastic foils consisting of a substrate in the form of a few hundereds nanometers with different elements of a relief put on this substrate. The laser pulse irradiated targets had relativistic intensity and femtosecond duration. It was found that the optimal relief is capable to increase absorption of a target to extremely high values. The shape of profile does not change significantly the absorption. For effective acceleration of ions the volume of relief should be less than the volume of the basic foil, otherwise absorption can be high but efficiency of ion acceleration low. The additional absorbed energy passes in energy of heavy ion components more effectively. To redirect energy to protons it is necessary to use a heterogeneous target. Laser pre-pulse is capable to destroy a relief and to change these results. With the account of laser pulse contrast larger relief and thicker foil can be the optimum.

Dispersion design of all-normal dispersive microstructured optical fibers for coherent supercontinuum generation

Paper 8073B-111 of Conference 8073B
Date: Tuesday, 19 April 2011
Time: 14:50 – 15:10

Author(s): Alexander Hartung, Institut für Photonische Technologien e.V. (Germany); Alexander M. Heidt, Stellenbosch Univ. (South Africa); Hartmut Bartelt, Institut für Photonische Technologien e.V. (Germany)

Recently, the generation of coherent, octave-spanning, and recompressable supercontinuum (SC) light has been demonstrated in optical fibers with all-normal group velocity dispersion (GVD) behavior by femtosecond pumping. In the normal dispersion regime, soliton dynamics are suppressed and the SC generation process is mainly due to self-phase modulation and optical wave breaking. This makes such white light sources suitable for time-resolved applications. The broadest spectra can be obtained when the pump wavelength equals the wavelength of maximum all-normal GVD. Therefore each available pump wavelength requires a specifically designed optical fiber with suitable GVD to unfold its full power. We investigate the possibilities to shift the all-normal maximum dispersion wavelength in microstructured optical fibers from the near infra red (NIR) to the ultra violet (UV). In general, a submicron guiding fiber core surrounded by a holey region is required to overcome the anomalous material dispersion of silica. Photonic crystal fibers (PCFs) with a hexagonal array of holes as well as suspended core fibers are simulated for this purpose over a wide field of parameters. The PCFs are varied concerning their air hole diameter and pitch and the suspended core fibers are varied concerning the number of supporting bridges and the bridge width. We show that these two fiber types complement each other well in their possible wavelength regions for all-normal GVD. While the PCFs are suitable for obtaining a maximum all-normal GVD in the NIR, suspended core fibers are applicable in the visible wavelength range.

Relaxation and interaction of electronic excitations induced by intense ultra short light pulses in scintillators

Paper 8077-31 of Conference 8077
Date: Tuesday, 19 April 2011
Time: 16:25 – 16:50

Author(s): Marco Kirm, Vitali Nagirnyi, Sebastian Vielhauer, Eduard Feldbach, Univ. of Tartu (Estonia)

Ultra short high intensity XUV light pulses (below 100 fs) supplied by novel accelerator-based free electron lasers (FEL), by high order harmonic generation (HHG) systems based on a Ti-Sapphire laser or by powerful femtosecond UV-lasers allow investigating relaxation processes and interaction of electronic excitations in scintillators under extreme density conditions. Recent years we have carried out such investigations for different scintillators (tungstates, doped rare-earth oxides, crystals with cross-luminescence) in non-linear regime at the exciting photon energies ranging from resonant conditions near intrinsic absorption edge to the deep core levels by means of time-resolved luminescence spectroscopy. Such investigation help to clarify causes of non-proportional response of scintillators, which is one of the key factors restricting their efficiency and energy resolution. The spatial density of thermalized electrons and holes, their transport and interaction as well as competition between radiative and non-radiative recombination are the main factors influencing the response of light converting materials. The decrease of the total luminescence yield and the shortening of the luminescence decay time as a function of excitation density are the main experimental evidences revealed. The latter one allows development of the quantitative model describing interaction of closely spaced excitations. Different light sources in wide excitation energy range gave us an opportunity to study such interaction for resonantly formed single excitations as well as for multiple spatially confined excitations created in inelastic scattering process of hot electrons. Defect formation will be also discussed.

Ferromagnet/superconductor bilayer nanostripes for optical-photon detection applications

Paper 8072A-18 of Conference 8072A
Date: Tuesday, 19 April 2011
Time: 17:10 – 17:40

Author(s): Giovanni P. Pepe, CNR-SPIN UOS Napoli (Italy) and Univ. degli Studi di Napoli Federico II (Italy); Loredana Parlato, Antonio Capretti, Vito Pagliarulo, Corrado De Lisio, Univ. degli Studi di Napoli Federico II (Italy) and CNR-SPIN UOS Napoli (Italy); Carmine Attanasio, Carla Cirillo, Univ. degli Studi di Salerno (Italy) and CNR-SPIN (Italy); Roberto Cristiano, Mikkel Ejrnaes, Istituto di Cibernetica Eduardo Caianiello (Italy); Hyroaki Myoren, Taino Toru, Saitama Univ. (Japan); Roman Sobolewski, Univ. of Rochester (United States)

Superconducting single-photon detectors (SSPDs), based on meander-type, ultrathin NbN nanostripes, are currently becoming optical-photon detectors of choice, due to their unique physical characteristics in terms of the response time, quantum efficiency, photon-number and energy resolving capabilities. Here, we investigate the use of the proximity effect in weak-ferromagnet/superconductor nano-layered heterostructures with the aim of enhancing the SSPD performances. We have fabricated and characterized nanostripe devices formed by NbN films (thickness < 8 nm) covered by 3-to-10 nm thick NiCu alloy over-layers. Large detector areas have been obtained by pattering our NbN/NiCu bilayers as an "in-series" connection of multiple, parallel nanostripe meander-type blocks; thus, realizing a so-called "cascade switch mechanism." The above geometry allows a cascade transition of all blocks after the photon absorption and, hence, results in a large voltage output. We ha performed femtosecond pump-probe spectroscopy at cryogenic temperatures down to 4 K, using 100-fs-wide, 850-nm-wavelength optical pulses with 82-MHz repetition rate. This study shows that the proximity effect influences the dynamics of photo-induced, nonequilibrium quasiparticles by significantly decreasing their energy relaxation time. Simultaneously, the investigation of the NbN/NiCu transport properties [i.e., current vs. voltage (I-V), critical current density vs. temperature, and magnetic critical field measurements] demonstrates a very large increase (up to a factor 6) of the critical current density in the proximitized nanostructures, as compared to the pure NbN nanostripes. The observed enhancement is due to the increase of the vortex pinning and correspondingly results in large photo-response voltage signals of our NbN/NiCu photodetectors. Finally, the presence of current steps on the I-V characteristics of our detectors indicated formation of phase-slip centers in the 2-dimensional nanostripes and suggested the possibility of a new photon detection mechanism in such mesoscopic heterostructures.

Ultrafast pump/probe diffraction and spectroscopy experiments with FEL radiation: setup development from the soft to the hard X-rays with the aim of studying chemical processes

Paper 8078-9 of Conference 8078
Date: Wednesday, 20 April 2011
Time: 14:20 – 14:40

Author(s): Ivan Rajkovic, Sebastian Gruebel, Rene More, Wilson Quevedo, Marcel Petri, Mirko Scholz, Simone Techert, Max-Planck-Institut für biophysikalische Chemie (Germany)

Recent developments of highly intense ultrashort X-ray radiation generated with the soft X-ray free electron lasers (FLASH) and the hard X-ray FEL (LCLS) allows for new kind of diffraction and spectroscopy experiments in chemistry and biochemistry. The additional coupling of an optical femtosecond laser enables for ultrafast time-resolved experiments of that kind: the optical laser excitation can be used to change the state of matter, to generate structures far away from equilibrium and initiate chemical or biochemical reactions with the advantage of an initial, optically well-defined and coherent excitation of the sample. The FEL pulse is then used to probe structure and electron evolution of the transiently formed state. By varying the time delay between optical laser pump and X-ray probe it is possible to perform these experiments in a time-resolved manner on an ultrafast timescale. For that purpose we developed a multipurpose vacuum chamber which function is to be used in the pump/probe diffraction / scattering and spectroscopy experiments with FEL radiation. By using a liquid jet setup to deliver the sample into the chamber it is possible to overcome the difficulties coming from the fact that a single shot of the FEL radiation is sufficient to induce irreversible damage to the sample. The refreshment of the sample allows for the experiments with the repetition rate of up to the MHz regime. The liquid jet nozzle size will be in the sub-micrometer range. This multipurpose chamber is in particular suited for chemistry and biochemistry experiments in solution.

Raman amplification of long laser beams to kilojoule energies and petawatt powers

Paper 8075-14 of Conference 8075
Date: Wednesday, 20 April 2011
Time: 16:20 – 16:50

Author(s): Raoul M. G. M. Trines, Robert Bingham, Peter A. Norreys, Rutherford Appleton Lab. (United Kingdom); Frederico Fiuza, Ricardo A. Fonseca, Luis O. Silva, Univ. Técnica de Lisboa (Portugal); Alan Cairns, Univ. of St. Andrews (United Kingdom)

The demonstration of fast-ignition (FI) inertial confinement fusion (ICF) requires the delivery of 40 kJ - 100 kJ of laser energy to the hot spot within 16 ps, assuming that the energy conversion from laser beams to fast electrons is in the range 20% - 50%. In addition, it is necessary to optimise $I\lambda^2$ to ensure that the hot electron energy falls within the correct range for stopping of the fast electrons, implying third harmonic conversion to 351 nm. High-energy picosecond petawatt beams at 351 nm are extremely difficult to generate using conventional solid-state laser systems. Previous studies of Raman amplification have concentrated on reaching the intensity frontier, which requires ultra-short pulses in the femtosecond regime [1]. Here we present novel particle-in-cell simulations, supported by analytic theory, that confirm that Raman amplification of high-energy nanosecond pulses in plasma can generate efficient petawatt peak power pulses of picosecond duration with high conversion efficiency (up to 60%), even at 351 nm wavelength [2]. This scheme provides a new route to explore the full parameter space for the realisation of the fast ignition inertial confinement fusion concept in the laboratory. This work also opens up a wide range of other high energy density physics research applications, including monochromatic K$_\alpha$ x-ray, proton beam and Compton radiography of dense plasmas, among many others. [1] R. Trines, F. Fiuza et al., Nature Physics 7, 87 (2011). [2] R. Trines, F. Fiuza et al., ArXiv 1102.0460 (2011).

Generation of nondiffracting subwavelength-beams in finite metal-dielectric structures

Paper 8070-34 of Conference 8070
Date: Wednesday, 20 April 2011
Time: 16:50 – 17:10

Author(s): Carlos J. Zapata-Rodriguez, David Pastor, Univ. de València (Spain); Juan J. Miret Mari, Maria T. Caballero Caballero, Vicent Camps Sanchis, Univ. de Alicante (Spain)

In this contribution we identify nano-structured devices sustaining out-of-plane NDBs with near-grazing propagation and transverse beam sizes clearly surpassing the diffraction limit of half a wavelength. This type of device consists of a planar multilayer metal-dielectric (MD) structure with a finite number of layers deposited on a solid substrate. The metallic and dielectric media are silver and fused silica respectively. Realistic material losses are also considered. The beam is launched from the substrate with a set of monochromatic PWs all having the same on-axis WV (β). In fact, we construct the NDB superposing only those PWs that are resonantly transmitted. Specifically, the system presents a series of transmission bands, which coincide with allowed bands of the infinite 1D MD. High transmission resonances appear within these bands, associated with the excitation of bound modes of the structure. We perform an optimization process concerning the layers width as free parameters in order to reach the most efficient and uniformly-transmitted resonances. Finally, the value of β and the focal placement are initially arbitrary and can be chosen according to the potential application. Possible applications include optical trapping and guiding of micro- and nano-size objects and femtosecond laser submicrochannel machining in glass.

FEL multilayer optics damaged by multiple shot laser beam: experimental results and discussion

Paper 8077-38 of Conference 8077
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Angelo Giglia, Consiglio Nazionale delle Ricerche (Italy); Nicola Mahne, Lab. Nazionale TASC (Italy); Anna Bianco, Cristian Svetina, Sincrotrone Trieste S.C.p.A. (Italy); Stefano Nannarone, Univ. di Modena e Reggio Emilia (Italy)

The irradiation effects of multiple femtosecond shots of a 400 nm laser beam with estimated fluences of some tens of mJ/cm2 on a EUV Mo/Si multilayer have been studied. The study has been motivated by the need of multilayer Mo/Si optics for the delay lines of the FEL source FERMI@Elettra, where these mirrors will be used to reflect 100 fs pulses at 13 nm with a fluence of some mJ/cm2. The analysis was carried on by means of different techniques as EUV and soft X-ray reflectivity, XPS, Total Electron Yield and Standing wave enhanced XPS. Measurements have been performed at the BEAR synchrotron beamline @ Elettra. Simulations have been carried on by means of a new home made software 'OPAL' for the calculation of the intensity of the electric field inside the stratified medium. Preliminary measurements have been performed also with a new fluorescence detector. A simple thermodynamic model have been also used to investigate the propagation of heat during the laser irradiation. AFM and SEM surface images have been also acquired. We observed a significant change in the multilayer performance at fluences of 100 mJ/cm2 and above with a significant reduction of reflectivity. Spectroscopic analysis allowed to correlate the decrease of reflectivity with the degradation of the multilayer stacking, ascribed to Mo-Si intermixing at the Mo/Si interfaces of the first layers, close to the surface of the mirror.

Ion imaging experiments at FLASH, LCLS, and SCSS

Paper 8078-28 of Conference 8078
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Daniel Rolles, Max-Planck-Institut für Kernphysik (Germany)

Results and conclusions drawn from various ion (and electron) imaging experiments performed at the three VUV and X-ray FELs currently in operation - FLASH, SCSS, and LCLS - will be presented. These include in particular pump-probe experiments on laser-aligned molecules performed with a double velocity map imaging (VMI) spectrometer at LCLS and ion-ion coincidence and electron-ion coincidence experiments using a reaction microscope (REMI) setup at FLASH, SCSS, and LCLS. In the former, diiodobenzene and dibromobenzene molecules were adiabatically aligned with a nanosecond IR-laser and the alignment was probed with the FEL pulse by means of ion imaging. In addition, the molecules were dissociated by a femtosecond IR-laser prior to the FEL pulse and ion and photoelectron images were recorded for various delays between IR-laser and FEL. The reaction microscope experiments range from coincidence experiments on various small and medium-sized molecules to VUV-pump-VUV-probe experiments performed at FLASH and SCSS with a split-mirror refocusing setup. These pump-probe experiments image directly the nuclear dynamics in photo-excited molecules and allow following chemical reactions such as isomerisations in real-time. In addition, they provide a means to perform autocorrelation experiments and to thus determine the FEL pulse length and coherence time. Based on our experiences at the three FEL facilities, a comparative analysis on the particular strengths and weaknesses of each machine for ion imaging experiments (e.g. with regards to the pulse patterns and repetition rates) will be attempted to conclude the presentation.

Performance benchmark of a gateable micro-channel plate detector for extreme ultraviolet radiation with high temporal resolution

Paper 8076-25 of Conference 8076
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Johannes Hauck, Ralf Freiberger, Larissa Juschkin, RWTH Aachen (Germany)

Research in ultrafast nanoscale phenomena requires high spatial and temporal resolution detectors. Optical imaging microscopes achieve high time resolution but low spatial resolution and scanning microscopes vice versa. Extreme ultraviolet imaging microscopy closes this gap but demands a suited two dimensional detector for efficient use of photons and simultaneously enabling fast gating. We use a micro-channel plate photoelectron multiplier together with a phosphor screen as detector. A channel spacing of 3 microns leads to a state-of-the-art spatial resolution. We pulse the operation voltage of the electron-multiplier during 1 ns. Only during that time the detector is highly sensitive to extreme ultraviolet light. We analyzed the following performances of the detector system: • Temporal behavior is measured by femtosecond illumination with a high harmonic generation laser at different relative delays. • Spatial resolution is determined by mapping the shadow of a sharp edge on the detector. The smearing gives information about the modulation transfer function. It could be shown that single channels are visible. • Spectral sensitivity of the detector is calibrated for extreme ultraviolet wavelengths ranging from 1 nm to 30 nm at the Physikalisch-Technische Bundesanstalt facility at the BESSY synchrotron in Berlin. In summary the detector leads to resolutions below 50 nm and shorter than 1 ns using a discharge produced plasma EUV source and a zone plate based microscope with a moderate magnification of ~ 250x. This is a highly interesting combination and will help understanding short time nanophysics in laboratory usage.

Towards a table top free-electron laser

Paper 8075-22 of Conference 8075
Date: Thursday, 21 April 2011
Time: 10:30 – 11:00

Author(s): Maria P. Anania, Enrico Brunetti, David Clark, Silvia Cipiccia, Riju Issac, Tom McCanny, Albert Reitsma, Richard P. Shanks, Gregor Welsh, S. Mark Wiggins, Univ. of Strathclyde (United Kingdom); Bas van der Geer, Marieke de Loos, Pulsar Physics (Netherlands); Mike Poole, Jim Clarke, Ben Shepherd, Daresbury Lab. (United Kingdom); Dino A. Jaroszynski, Univ. of Strathclyde (United Kingdom)

Recent progress in developing laser-plasma accelerators is raising the possibility of a compact coherent radiation source that could be housed in a medium sized university department. Furthermore, since the duration of electron bunches from laser-plasma wakefield accelerators (LWFAs) is determined by the relativistic plasma wavelength, radiation sources based on these accelerators can produce pulses with femtosecond durations. Beam properties from laser-plasma accelerators have been traditionally thought of as not being of sufficient quality to produce amplification. However, our work shows that this is not the case. Here, we present a study of the beam characteristics of a laser-plasma accelerator and the compact ALPHA-X (Advanced Laser Plasma High-energy Accelerators towards X-rays) free-electron laser (FEL). We will present a study of the influence of beam transport on FEL action in the undulator, paying particular attention to bunch dispersion in the undulator. We will also show how the electron beam properties can be optimized to allow FEL lasing in the VUV region. We will also present simulations that have been performed using the beam properties measured on the ALPHA-X beam line. This is an important step for developing a compact synchrotron source or a SASE free-electron laser.

Observation of the optical peregrine soliton

Paper 8071-27 of Conference 8071
Date: Thursday, 21 April 2011
Time: 12:10 – 12:30

Author(s): Bertrand Kibler, Kamal Hammani, Julien Fatome, Christophe Finot, Guy Millot, Univ. de Bourgogne (France); Frederic Dias, Ecole Normale Supérieure de Cachan (France) and Univ. College Dublin (Ireland); Goery Genty, Tampere Univ. of Technology (Finland); Nail Akhmediev, The Australian National Univ. (Australia); John M. Dudley, Univ. de Franche-Comté (France)

We report the first experimental observation of the optical Peregrine soliton, a novel class of nonlinear localized structure first predicted to exist over 25 years ago. Our results confirm the increasingly important role that experiments in optics play in providing insight into wider areas of nonlinear physics. In optics, the most well-known solitons are the hyperbolic secant envelope solitons of the nonlinear Schrodinger equation (NLSE), but the NLSE admits many other classes of localised structure, and there has been significant interest in soliton solutions existing upon a finite background. One particular structure of this type is the Peregrine soliton which surprisingly has never been the subject of any systematic experimental study. The Peregrine soliton is of fundamental significance because it is a two dimensional soliton localised in both time and space, and because it defines the limit of a wide class of solutions to the NLSE. A weakly modulated CW field injected into an anomalous dispersive fiber described by the standard NLSE undergoes induced modulation instability where the modulation cycles of the field experience temporal compression and amplification. At the low-frequency limit of this process, the Peregrine soliton is excited, associated with a simple polynomial form for the field amplitude. In this study, we implement experiments in optical fibre generating femtosecond pulses with strong temporal and spatial localization, and near-ideal temporal Peregrine soliton characteristics. Experimental measurements using autocorrelation, spectral analysis and frequency-resolved optical gating were used to measure the reshaping of the input field towards the solution predicted by Peregrine.

Time resolved EUV pump-probe microscopy of fs-LASER induced nanostructure formation

Paper 8076-19 of Conference 8076
Date: Thursday, 21 April 2011
Time: 13:30 – 13:50

Author(s): Ralf Freiberger, Johannes Hauck, Martin Reininghaus, Dirk Wortmann, Larissa Juschkin, RWTH Aachen (Germany)

We report on our efforts on setting up and building a compact Extreme Ultraviolet (EUV)-pump-probe microscope. The goal is the observation of femtosecond (fs)-laser induced nanostructure formation. The unique interaction processes induced by fs-laser radiation open up new markets in laser material processing and are therefore matter of actual research. "Sub 100 nm"-structures offer vast potential benefits in photonics, biotechnology, tribological surface design, plasmonic applications and production of nanoparticles. Focused fs-laser radiation causes a local modification resulting in nanostructures of high precision and reproducibility. However the formation dynamics is not well understood. Research in this field requires high temporal and spatial resolution. A combination of fs-laser and EUV-microscope provides a tool for "in situ"-observation of the formation dynamics. As exemplary structures to be investigated, we use nanojets on thin gold films and periodic surface structures (ripples) on dielectrics. In the future, the EUV-pump-probe microscope can become a versatile tool to observe physical or biological processes. Microscopy using EUV-light is capable of detecting structures on a scale down to several tens of nanometers. For detailed investigations a compact EUV-microscope has been realized utilizing OVI Balmer-alpha radiation at 17.3 nm coming from a discharge produced oxygen plasma. As optical elements a grazing incidence elliptical collector and a zone plate with a width of outermost zone of 50 nm and a spectral filter to avoid chromatic aberrations are used. The detector is a fast gated microchannel plate with a pore size of 2 microns contacted by a low impedance transmission line, so that we expect resolutions smaller than 100 nm and better than 1 ns. The newly developed EUV-microscope is a powerful tool for a wide field of investigations that need high time and spatial resolutions.

Quasi-phase-matched third harmonic generation in optical fibers using refractive-index gratings

Paper 8071-30 of Conference 8071
Date: Thursday, 21 April 2011
Time: 14:30 – 14:50

Author(s): Karol Tarnowski, Wroclaw Univ. of Technology (Poland); Bertrand Kibler, Christophe Finot, Univ. de Bourgogne (France); Waclaw Urbanczyk, Wroclaw Univ. of Technology (Poland)

The purpose of this work is to demonstrate the quasi-phase-matching of third harmonic generation process in photonic crystal fibers using refractive-index gratings. We compare conversion efficiency calculated with analytical coupled modes theory and numerical approach employing the generalized nonlinear Schrödinger equation. We discuss the effect on conversion efficiency of several parameters including pump power, mode field diameter, glass nonlinearity and grating modulation depth. Moreover, we show that introducing the phase matching condition that takes into account the nonlinear contribution to propagation constants significantly increases the conversion efficiency by several orders of magnitude. Our results show not only that the grating must satisfy the nonlinear quasi-phase matching condition but also that we must take into account the modulation of the grating nonlinear parameters in order to reach the maximum conversion efficiency. For the optimum grating period in a standard single-mode optical fiber, the efficiency reaching 20% over the propagation distance of 45 cm can be achieved, whereas in fiber without grating the maximum efficiency is only 10-7. Nevertheless, we outline that even small detunings from the phase matching condition can be very destructive to the process. Finally, we study a possible way of further improvement of the efficiency through the application of a microstructured fiber with small mode area and high nonlinearity. Indeed, an increase of efficiency is expected by application of high power femtosecond pump pulses, which requires here a special fiber design matching the group velocity at pump and third harmonic frequencies to avoid the effect of pulse walk-off.

Multiphoton

Enhanced resolution in lossy phase estimation by optical parametric amplification

Paper 8072B-22 of Conference 8072B
Date: Monday, 18 April 2011
Time: 11:10 – 11:30

Author(s): Nicolò Spagnolo, Chiara Vitelli, Univ. degli Studi di Roma La Sapienza (Italy) and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (Italy); Lorenzo Toffoli, Univ. degli Studi di Roma La Sapienza (Italy); Francesco De Martini, Univ. degli Studi di Roma La Sapienza (Italy) and Accademia Nazionale dei Lincei (Italy); Fabio Sciarrino, Univ. degli Studi di Roma La Sapienza (Italy) and Istituto Nazionale di Ottica (Italy)

The aim of quantum sensing is to develop quantum strategies in order to achieve the best possible precision in the estimation of an unknown parameter with minimal disturbance upon the system. In optical phase estimation, an interferometric approach is typically exploited in order to measure an unknown phase shift introduced by a sample. However, most of the protocols developed up to now have been tailored for a noise-free scenario, thus reducing their potential applications in typical experimental conditions. Here we propose to exploit optical parametric amplification to enhance the resolution in a minimally-invasive phase estimation context in the presence of losses. By performing the amplification process on the microscopic probe after the interaction with the sample, we can broadcast the information on the phase into a larger number of particles. This strategy allows to compensate for losses that occur after the amplification process, that is, at the transmission and at the detection stages. Furthermore, it remains minimally-invasive on the sample since the amplification process is performed after the interaction. We have studied and experimentally tested the amplification interferometric measurement strategy with a single-photon probe, and by comparing the achieved sensitivity with and without the optical parametric amplifier. The enhancement obtained with our strategy in the phase estimation is much greater than one, and reaches the experimental value of 200 for high losses eta =10^(-4). Further investigation will be devoted to the generalization of this protocol with more general probe state with respect to single photons.

Ultrafast atomic and molecular photoionization at the LCLS

Paper 8078-6 of Conference 8078
Date: Wednesday, 20 April 2011
Time: 11:40 – 12:10

Author(s): John D. Bozek, Christoph Bostedt, Sebastian Schorb, SLAC National Accelerator Lab. (United States)

The atomic, molecular and optical physics instrument at the LCLS has been used for approximately 30 experiments at the LCLS x-ray free electron laser at the SLAC National Accelerator Laboratory. The instrument has been used to study the interaction of ultrafast and ultraintense x-rays with atoms, molecules and clusters as intended but has also been used in the study of warm dense matter, material damage, and inorganic and biological particle imaging. Initial experiments on the ionization of atoms and molecules conducted in the fall of 2009 have already resulted in the publication of five peer-reviewed articles at the time of writing of this abstract, with many more to follow.

Enhanced resolution in lossy phase estimation by optical parametric amplification

Paper 8072B-22 of Conference 8072B
Date: Monday, 18 April 2011
Time: 11:10 – 11:30

Author(s): Nicolò Spagnolo, Chiara Vitelli, Univ. degli Studi di Roma La Sapienza (Italy) and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (Italy); Lorenzo Toffoli, Univ. degli Studi di Roma La Sapienza (Italy); Francesco De Martini, Univ. degli Studi di Roma La Sapienza (Italy) and Accademia Nazionale dei Lincei (Italy); Fabio Sciarrino, Univ. degli Studi di Roma La Sapienza (Italy) and Istituto Nazionale di Ottica (Italy)

The aim of quantum sensing is to develop quantum strategies in order to achieve the best possible precision in the estimation of an unknown parameter with minimal disturbance upon the system. In optical phase estimation, an interferometric approach is typically exploited in order to measure an unknown phase shift introduced by a sample. However, most of the protocols developed up to now have been tailored for a noise-free scenario, thus reducing their potential applications in typical experimental conditions. Here we propose to exploit optical parametric amplification to enhance the resolution in a minimally-invasive phase estimation context in the presence of losses. By performing the amplification process on the microscopic probe after the interaction with the sample, we can broadcast the information on the phase into a larger number of particles. This strategy allows to compensate for losses that occur after the amplification process, that is, at the transmission and at the detection stages. Furthermore, it remains minimally-invasive on the sample since the amplification process is performed after the interaction. We have studied and experimentally tested the amplification interferometric measurement strategy with a single-photon probe, and by comparing the achieved sensitivity with and without the optical parametric amplifier. The enhancement obtained with our strategy in the phase estimation is much greater than one, and reaches the experimental value of 200 for high losses eta =10^(-4). Further investigation will be devoted to the generalization of this protocol with more general probe state with respect to single photons.

Ultrafast atomic and molecular photoionization at the LCLS

Paper 8078-6 of Conference 8078
Date: Wednesday, 20 April 2011
Time: 11:40 – 12:10

Author(s): John D. Bozek, Christoph Bostedt, Sebastian Schorb, SLAC National Accelerator Lab. (United States)

The atomic, molecular and optical physics instrument at the LCLS has been used for approximately 30 experiments at the LCLS x-ray free electron laser at the SLAC National Accelerator Laboratory. The instrument has been used to study the interaction of ultrafast and ultraintense x-rays with atoms, molecules and clusters as intended but has also been used in the study of warm dense matter, material damage, and inorganic and biological particle imaging. Initial experiments on the ionization of atoms and molecules conducted in the fall of 2009 have already resulted in the publication of five peer-reviewed articles at the time of writing of this abstract, with many more to follow.

Prime number decomposition: the hyperbolic function, Gauss sums and multi-path interference

Paper 8072B-27 of Conference 8072B
Date: Monday, 18 April 2011
Time: 14:30 – 14:50

Author(s): Vincenzo Tamma, Carroll O. Alley, Univ. of Maryland, Baltimore County (United States); Augusto Garuccio, Univ. degli Studi di Bari (Italy); Wolfgang P. Schleich, Univ. Ulm (Germany); Yanhua Shih, Univ. of Maryland, Baltimore County (United States)

Interference of probability amplitudes rather than addition of probabilities is the central lesson of quantum mechanics. The problem of factoring numbers using interference in a classical device, such as a Michelson interferometer, or in a quantum system, characterized by multi-photon quantum interference is part of the much broader theme of connecting the fields of quantum mechanics and number theory. Indeed, it is the periodicity as expressed by the modular functions used in Shor method that is at the heart of the algorithm. Such functions are closely connected to Gauss sums which also manifest remarkable periodicity properties. Motivated by the power of interference and by the periodicity characterizing Gauss sums we use in the present paper interference in a multi-path Michelson interferometer to encode the hyperbolic function into a sequence of generalized curlicue functions. The locations of the central maxima of the resulting optical interferogram allow us to factor numbers as demonstrated by a recent experiment. A novel factoring algorithm which takes advantage of a remarkable scaling property induced the functional dependence on the hyperbolic function allows us to recognize the factors by measuring a number of interferograms scaling logarithmically with respect to the largest number to be factored. The connection between Shor modular functions and Gauss sums at the core of this work serves as a motivation to extend such a parallelism between the two methods to the use of quantum interference in a binary representation in order to achieve a polynomial scaling in the number of resources.

On the design of experiments for the study of extreme field limits in the ultra-relativistic interaction of electromagnetic waves with plasmas

Paper 8080B-58 of Conference 8080B
Date: Wednesday, 20 April 2011
Time: 9:00 – 9:30

Author(s): Sergei V. Bulanov, Timur Z. Esirkepov, Japan Atomic Energy Agency (Japan)

On the Design of Experiments for the Study of Extreme Field Limits in the Ultra-Relativistic Interaction of Electromagnetic Waves with Plasmas S. V. Bulanov-a, T. Zh. Esirkepov-a, Y. Hayashi-a, M. Kando-a, H. Kiriyama-a, J. K. Koga-a, K. Kondo-a, H. Kotaki-a, A. S. Pirozhkov-a, Y. Kato-b, S. S. Bulanov-c, A. G. Zhidkov-d, G. Korn-e a-Advanced Photon Research Center, JAEA, Kizugawa, Kyoto,619-0216 Japan b-The Graduate School for the Creation of New Photonics Industries, Hamamatsu, Japan c-University of California, Berkeley, CA 94720, USA d-Central Research Institute of Electric Power Industry, Yokosuka, Kanagawa, Japan e-Max-Planck-Institut fuer Quantenoptik, Garching, Germany Abstract. We discuss how to conduct the experiments on the collision of laser light and high intensity electromagnetic pulses generated by relativistic flying mirrors, with electron bunches produced by a conventional accelerator and with laser wake field accelerated electrons for studying extreme field limits in the nonlinear interaction of electromagnetic waves. The regimes of dominant radiation reaction, which completely changes the electromagnetic wave-matter interaction, can be revealed in the laser plasma experiments. This will result in a new powerful source of ultra short high brightness gamma-ray pulses. A possibility of demonstration of the electron-positron pair creation in vacuum in a multi-photon processes can be realized. This will allow modelling under the terrestrial laboratory conditions the neutron star magnetospheres, the cosmological gamma ray bursts and Leptonic Era of the Universe.

Multi-threaded parallel simulation of non-local non-linear problems in ultrashort laser pulse propagation in the presence of plasma

Paper 8071-41 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Mandana Baregheh, Aston Univ. (United Kingdom); Holger Schmitz, Imperial College London (United Kingdom); Vladimir K. Mezentsev, Aston Univ. (United Kingdom)

We describe a parallel multi-threaded approach for high performance modelling of wide class of phenomena in ultrafast non-linear optics. Non-linear wave equation in the form of the Generalised Non-Linear Schroedinger Equation (GNLSE) is a generic mathematical model describing narrow bandwidth wave propagation in envelope approximation. In this paper we consider a parallel numerical solution for a specific model which describes femtosecond laser pulse propagation in transparent media. In this case GNLSE is coupled to Drude model of plasma resulting from multi-photon and avalanche ionisation processes. However our approach can be extended to similar models. We compare performance of the multithreaded parallel code implemented for Nvidia Graphics Processing Units using CUDA programming interface with a serial CPU version. Coupling between the equations makes GNLSE non-local which results in impossible straightforward parallel implementation. To simplify the problem, the splitting operator method is used to reduce GNLSE it into a succession of linear and non-linear steps. The linear term is solved in frequency domain using CUDA's multi-threaded version of the Fast Fourier Transform. The parallel simulation of the non-linear term is not straightforward due to non-locality induced by coupling between plasma and electromagnetic wave. We develop the parallel numerical solution of non-linear step by expressing the non-linear problem as an integral equation in time domain. We have managed to successfully parallelise solution of GNLSE non-locally coupled with plasma using CUDA interface. We have tested the accuracy of the results and found satisfactory linear scaling up with 10x to 30x factor of speedup on Nvidia Tesla C1060 compared to CPU implementation.

Rapid prototyping of color structures using 3D laser lithography

Paper 8071-32 of Conference 8071
Date: Thursday, 21 April 2011
Time: 14:50 – 15:10

Author(s): Pirmin Proier, Volker Schmidt, Ma R. Belegratis, Barbara Stadlober, Paul Hartmann, JOANNEUM RESEARCH Forschungsgesellschaft mbH (Austria); Joachim Krenn, Karl-Franzens-Univ. Graz (Austria)

Nature is colorful. Inspired by feathers, insects and plants, we try to produce brilliant colored surfaces, resulting from structures on the scale of the wavelength of the ambient light. Employing 3D laser lithography based on two-photon- absorption, the structures are written into a photosensitive polymer. A highly intense pulsed laser in the near infrared is focused into a spot within the photosensitive material and moved along the confines of a selected structure. The material itself is transparent for the used wavelength, but within the laser's focal volume the probability of multi-photon absorption is strongly increased and leads to local polymerisation. The produced structures look similar to stretched trees with varying heights; they exhibit lamellas of high index polymerised material surrounded by air. This index difference leads to diffraction and interference of light within a lamella, resulting in a wavelength-dependent reflectance and as a consequence to a colored surface. The observed colors display a strong brilliance and an excellent uniformity with respect to the observation angle. This procedure could prove beneficial for prototyping of bionic structures and for a better understanding of their principles. Compared to pigments, the resulting colors are strong and long-lasting.

Biphoton compression in standard optical fiber

Paper 8071-29 of Conference 8071
Date: Thursday, 21 April 2011
Time: 14:10 – 14:30

Author(s): Alice Meda, Istituto Nazionale di Ricerca Metrologica (Italy)

Generation of two-photon light with given spectral and temporal properties it's of great interest for quantum communication and quantum metrology applications. In particular, preparation of biphotons with ultra-narrow correlation time is a very important task. In a recent series of papers [1, 2], our group analyzed the production of two-photon wavepackets, by means of spontaneous parametric down conversion emission, in crystals with linearly chirped quasi-phase matching grating. Wavepackets present very broad spectra but a broad spectrum does not necessarily imply small correlation times, although the inverse is true. Indeed, the spectrum broadening induced by the grating is inhomogeneous; for this reason, the two-photon spectral amplitude presents a phase (a frequency chirp) that depends nonlinearly on the frequency. Hence, the two-photon wavepackets are not Fourier transform-limited. As suggested in [3], the ideal way to make the wavepacket perfectly transform limited is to insert in the path of the biphotons a proper optical medium that compensates the non-linear part of the phase factor present in the spectral amplitude. In our work, we investigate the non-local temporal compression of the photons induced by the insertion of a standard optical fibre in the path of one of the two photons. We present and discuss systematic study of this phenomenon and some optimal situation where the full numerical calculation shows an effect that can be clearly observed with a realistic set-up. The study has open the way to the practical realization of this idea[4]. [1] G. Brida, M. V. Chekhova, I. P. Degiovanni, M. Genovese, G. Kh. Kitaeva, A. Meda and O. A. Shumilkina, Phys. Rev. Lett. 103, 193602 (2009). [2] G. Brida, M. V. Chekhova, I. P. Degiovanni, M. Genovese, G. Kh. Kitaeva, A. Meda and O. A. Shumilkina, Phys. Rev. A 81, 053828 (2010). [3] S. E. Harris, Phys. Rev. Lett. 98, 063602 (2007). [4] S. Sensarn, G. Y. Yin, and S. E. Harris, Phys. Rev. Lett. 104, 253602 (2010).

Nonlinear optical properties of silver nanoparticles synthesized in ORMOCER by ion implantation

Paper 8071-13 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 11:20 – 11:40

Author(s): Andrey L. Stepanov, E.K. Zavoisky Physical-Technical Institute (Russian Federation); Roman Kiyan, Laser Zentrum Hannover e.V. (Germany); Vladimir Nuzhdin, Valery Valeev, E.K. Zavoisky Physical-Technical Institute (Russian Federation); Boris N. Chichkov, Laser Zentrum Hannover e.V. (Germany)

First experimental results on a synthesis of metal nanoparticles in ORMOCER by ion implantation and nonlinear optical properties of such composite are presented. Silver ions were implanted into organic/inorganic matrix at an accelerating energy of 30 keV and doses in the range from 0.25⋅1017 to 0.75⋅1017 ion/cm2. The silver ions form metal nanoparticles, which demonstrated surface plasmon absorption at the wavelength of 425-580 nm. The nonlinear absorption of composites was measured by z-scan technique using 150 fs laser pulses at 780 nm. ORMOCER with silver nanoparticles shows nonlinear saturation absorption, than matrix itself demonstrates two-photon absorption. Superposition on two nonlinear absorptions in same composite material is discussed.

Light up-conversion and single photon directional emission beaming from quantum dots embedded in subwavelength metallic nano-slit arrays

Paper 8071-14 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 11:40 – 12:00

Author(s): Ronen Rapaport, The Hebrew Univ. of Jerusalem (Israel)

We show a large, 20-fold enhancement of two-photon absorption processes in nanocrystal quantum dots and of light upconversion using a hybrid optical device in which near-IR emitting InAs nanocrystal quantum dots were embedded in a metallic nanoslit array. We also demonstrate a directional beaming of the photons that are emitted from these quantum dots with a divergence angle of less than 4 degrees. The resonant enhancement of the nonlinear optical processes is due to the strong local electromagnetic field enhancements inside the nanoslit array structure at the extraordinary transmission (EOT) resonances. The photon beaming is achieved using the resonant coupling of the quantum dots to the Bragg standing EOT modes, where exciton - plasmon polariton coupling dominates the emission properties of the quantum dots. We show this beaming effect down to the single quantum dot - single photon level. Therefore we conclude that engineering structures which incorporate nanocrystal quantum dots with subwavelength metallic nanostructures is a promising way for a range of new types of active optical devices, allowing new ways to manipulate and control the optical properties of these nano-emitters.

Superconducting single photon detectors based on parallel NbN nanowires

Paper 8072A-2 of Conference 8072A
Date: Tuesday, 19 April 2011
Time: 9:00 – 9:30

Author(s): Mikkel Ejrnaes, Istituto di Cibernetica Eduardo Caianiello (Italy); Alessandro Casaburi, Sergio Pagano, Univ. degli Studi di Salerno (Italy); Francesco Mattioli, Alessandro Gaggero, Roberto Leoni, Istituto di Fotonica e Nanotecnologie (Italy); Roberto Cristiano, Istituto di Cibernetica Eduardo Caianiello (Italy)

Superconducting single photon detectors (SSPD) based on ultrathin NbN nanowires are of significant current interest for long distance quantum optics applications due to their good efficiency, dark count rate and timing jitter at 1550 nm wavelength. Current SSPD research is focusing on the use of parallel nanowires for achieving pseudo photon number resolution, increasing the efficiency at longer wavelengths and increasing the area coverage. When increasing the SSPD area one must face both the problem of maintaining nanowire uniformity across large areas and also avoid the decrease in SSPD operation speed. Here we present how these problems can be overcome using parallel nanowires and show our results on SSPDs with area coverage up to 40 x 40 µm2 based on 100 nm wide ultrathin NbN nanostrips with a 40% filling factor. Using a standard SSPD operation we achieved a maximum count rate of 33 MHz which is faster than the standard meandered serial SSPDs. Furthermore, using an innovative operation procedure, that exploits the large signal amplitude of our parallel nanowire SSPDs, we could achieve 80 MHz operation. Due to the large area coverage we also identified a new operation region with two-photon sensitivity which we argue could be used to make a sampling photon number resolution SSPD. The increase in SSPD area coverage should open the way towards applications using multimode fibers or irregular photon emitters.

Cross phase modulation in photonic crystals

Paper 8071-6 of Conference 8071
Date: Tuesday, 19 April 2011
Time: 16:10 – 16:30

Author(s): Karolina Slowik, Nicolaus Copernicus Univ. (Poland); Maurizio Artoni, Univ. degli Studi di Brescia (Italy); Giuseppe C. La Rocca, Scuola Normale Superiore di Pisa (Italy); Andrzej Raczynski, Jaroslaw Zaremba, Sylwia Zielinska-Kaniasty, Nicolaus Copernicus Univ. (Poland)

Our work belongs to a large group of studies devoted to engineering optical properties of atomic media by optical means. Those investigations have in view far going applications in information processing, in particular constructing optical elements like quantum switches or gates. We consider a simultaneous propagation of two weak pulses (the 'probe' and 'trigger') in the tripod configuration atomic medium irradiated by a strong control field. Such a system provides conditions similar to those present in the electromagnetically induced transparency phenomenon, when an originally absorptive medium becomes transparent for both probe and trigger due to the control field. In such situation a usually weak interaction between two photons may become enhanced by many orders of magnitude. This gives rise to nonlinear effects, i.e. large cross phase modulation which allows for constructing a polarization phase gate. A wide area of investigations opens when the control field is taken in the standing wave form, leading to periodic modulation of the refractive index of the medium which now becomes a photonic crystal. While propagating in such a medium both probe and trigger are split into transmitted and reflected components whose nonlinear phase shifts are of particular interest. In our approach we calculate the nonlinear periodic susceptibilities and make numerous simulations of the propagation of the pulses in different conditions. We calculate the phases of the outgoing fields and find the optimal values of parameters characterizing the system, i.e. when the nonlinear phase shifts of both transmitted and reflected probe and trigger components are large. We show a convenient way of controlling the process by shifting the frequency of the incoming probe. We plot the transmission and reflection spectra for different values of parameters of the system.

Permanent wavegides in glassy As4Ge30S66 induced by femtosecond filaments

Paper 8071-21 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 17:00 – 17:20

Author(s): Viktor M. Kadan, Ivan V. Blonsky, Institute of Physics (Ukraine); Oleh I. Shpotyuk, Lviv Scientific Research Institute of Materials (Ukraine) and J. Dlugosz Univ. de Czestochowa (Poland); Mihail S. Iovu, Institute of Applied Physics (Moldova); Petro Korenyuk, Institute of Physics (Ukraine)

We report the first observation of the femtosecond filaments and filament-induced permanent waveguides in bulky ChGs exemplified by a glassy As4Ge30S66. This wide-gap (3.0 eV) ChG has been synthesizes to reduce the two-photon absorption (2PA) which prevents the filament formation in more narrow-gap ChGs. We focus the femtosecond laser beam (110 nJ, 150 fs, 800 nm, 1 kHz) into a 3 mm thick sample at different pulse energies, exposures T, and positions of the beam waist inside the sample. The near-field beam profiles are measured on the exiting face of the sample. A reversible Kerr filament of 4.8 µm core diameter and of 1.8 mm length forms at T ≤ 10 s, while at T ≥ 25 s, a permanent waveguide appears. Two principal mechanisms are involved in the waveguide formation. First the Kerr filament forms, while the formation of the permanent waveguide occurs later due to the positive Δn build-up on the filament axis. A physical reason for the permanent index change is the generation of free carriers by 2PA in the filament core, which trigger structural transformation in the material. The Δn profile of the waveguide is numerically recovered from its defocused microscopic transmission images, applying 1D transport-of-intensity equation and inversed Abel transform. The index profile features positive axial Δn, enveloped by a negative zone. Such a shape of the profile suggests the axial densification of the material, while the tensile stress generates the enveloping area of decreased index.

SROP and DROP spectra with alkali atomic vapor cell and applications

Paper 8072B-35 of Conference 8072B
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): Junmin Wang, Qiangbing Liang, Jing Gao, Baodong Yang, Tiancai Zhang, Kunchi Peng, Shanxi Univ. (China)

Two schemes of Doppler-free high-resolution velocity-selective optical-pumping (VSOP) atomic spectroscopy, called single-resonance optical pumping (SROP) and double-resonance optical pumping (DROP), are performed in room-temperature cesium and rubidium vapor cells. SROP and DROP signals actually indicate the variation of the zero-velocity atom population of one hyperfine fold of ground state, and this population variation is due to velocity-selective optical pumping from one hyperfine fold of ground state to another via one-photon excitation or cascade two-photon excitation and thereafter decay processes. 1)SROP scheme is employed to measure the dressed-state splitting of 133Cs 6S_1/2 (F=4) ground state with cesium vapor cell,but normally the dressed-state splitting of atomic ground state only can be detected with laser-cooled atomic sample. 2)DROP scheme can remarkably improve SNR of spectroscopic signal of a transition between atomic excited states. With 87Rb 5S_1/2 (F=2) - 5P_3/2 (F'=3) - 4_D3/2 ladder-type system, DROP spectra are obtained and compared with conventional optical-optical double-resonance (OODR) spectra. Co-propagating (CP) and counter-propagating (CTP) configurations are also compared. Thanks to EIT in ladder-type atomic system with the CTP configuration, DROP spectra for 87Rb 5P_3/2 (F'=3) - 4D_3/2 transitions around 1529nm are achieved with rubidium vapor cell. And a 1529-nm diode laser's frequency is preliminarily stabilized via DROP scheme, and clearly CTP-DROP scheme greatly improves the frequency stability, which is significant in optical telecommunication field for correction of the communication channels in DWDM system.

Fabrication and characterisation of metallised woodpile structures

Paper 8070-21 of Conference 8070
Date: Thursday, 21 April 2011
Time: 9:20 – 9:40

Author(s): Maksim Zalkovskij, Radu I. Malureanu, Andrei Andryieuski, Andrei Lavrinenko, Technical Univ. of Denmark (Denmark)

The request for fabrication and characterization 3D structures possessing desired functionalities has boosted in the last years. The so-called woodpile structures (WpSs) have a great potential in nanophotonics exhibiting broad functionality and controlled adjustment of their behaviour. Due to their 3D tunability, WpSs can be used as superprisms, 3D photonic crystals with complete bandgaps and even invisibility cloaks. In this paper we report on fabrication and characterisation of metal-coated WpSs. The structures were fabricated using the two photon polymerisation technique. To increase their functionality, we developed an electroless based technique for depositing thin layers of silver on 3D structures. In spite that silver is the best optical metal its deposition with controlled characteristics is far from trivial. Although, there are other techniques for depositing metals on 3D structures, they require huge optimisation efforts due to the multiple-parameter space or conductive substrates thus limiting the coating possibilities. The characterisation of WpSs is generally based on measurements and simulations of the bulk while the border effects are usually ignored. By measuring the transmission characteristics at the edge of these structures we show pronounced differences with respect to the bulk. Also, the transmission at the border of the structure shows peculiar characteristics like enhanced transmission spectra at different wavelengths and in different directions. We present here both the silver deposition technique and transmission/reflection results in the bulk as well as close to the edges of the structures.

Rapid prototyping of color structures using 3D laser lithography

Paper 8071-32 of Conference 8071
Date: Thursday, 21 April 2011
Time: 14:50 – 15:10

Author(s): Pirmin Proier, Volker Schmidt, Ma R. Belegratis, Barbara Stadlober, Paul Hartmann, JOANNEUM RESEARCH Forschungsgesellschaft mbH (Austria); Joachim Krenn, Karl-Franzens-Univ. Graz (Austria)

Nature is colorful. Inspired by feathers, insects and plants, we try to produce brilliant colored surfaces, resulting from structures on the scale of the wavelength of the ambient light. Employing 3D laser lithography based on two-photon- absorption, the structures are written into a photosensitive polymer. A highly intense pulsed laser in the near infrared is focused into a spot within the photosensitive material and moved along the confines of a selected structure. The material itself is transparent for the used wavelength, but within the laser's focal volume the probability of multi-photon absorption is strongly increased and leads to local polymerisation. The produced structures look similar to stretched trees with varying heights; they exhibit lamellas of high index polymerised material surrounded by air. This index difference leads to diffraction and interference of light within a lamella, resulting in a wavelength-dependent reflectance and as a consequence to a colored surface. The observed colors display a strong brilliance and an excellent uniformity with respect to the observation angle. This procedure could prove beneficial for prototyping of bionic structures and for a better understanding of their principles. Compared to pigments, the resulting colors are strong and long-lasting.

Optical and nonlinear optical studies of Ba0.5Sr0.5TiO3 thin films

Paper 8071-47 of Conference 8071
Date: Wednesday, 20 April 2011
Time: 17:40

Author(s): K. Venkata Saravanan, K. C. James Raju, M. Ghanashyam Krishna, Surya Prakash Tewari, Soma Venugopal Rao, Univ. of Hyderabad (India)

Herein we present our detailed experimental results on the physical, linear, and nonlinear optical properties of rf sputtered Ba0.5Sr0.5TiO3 (BST) films deposited on MgO substrates at different deposition temperatures (Td), ranging from 500oC to 800oC. X-ray diffraction studies revealed that the films deposited at 500oC were amorphous in nature. The films deposited at 600oC were preferentially oriented along (111) direction whereas films deposited at 700oC and 800oC were oriented along (110) and (200) directions, respectively. Scanning Probe Microscopic studies showed that the surface of the BST5 films deposited at 500oC was smooth (RMSroughness = 0.7 nm) and the films deposited at 600oC had an RMSroughness value of ~8.7 nm which decreased to ~3.3 and ~2.2 nm for the films deposited at 700 and 800oC, respectively. The linear refractive index (n0) and optical band gap (Eg) determined from the transmission spectra indicated that n0 increased from 1.97 to 2.21 and Eg decreased from 4.2 to 3.7 eV with increase in Td from 500oC to 800oC. The nonlinear absorption studies were performed near 800 nm using ~2 ps and ~25 ps pulses with the Z-scan technique. The nonlinear absorption switched from reverse saturable absorption type in the films deposited at Td <600oC to three-photon absorption (3PA) in the films deposited at Td >600oC. The magnitude of the 3PA coefficient was estimated to be ~10^-21 cm3/W2. The variation of nonlinear coefficients with growth conditions is studied and explained.

Finite element modelling of induced gratings in nonlinear optics

Paper 8071-33 of Conference 8071
Date: Thursday, 21 April 2011
Time: 15:40 – 16:00

Author(s): Pierre Godard, Frederic Zolla, André Nicolet, Institut Fresnel (France)

In this paper, we present a multiharmonic model able to allow for general nonlinear optical media. As a particular example, two- and three-photon processes are considered here. The numerical model is based on the finite element method that allows to take into account the inhomogeneities of the refraction index due to the nonlinearities. It consists of several harmonic equations at various frequencies coupled via some nonlinear terms. As an illustration we propose a simple homogeneous uniform slab made of non-linear material but illuminated by three plane waves in order to create an artificial periodic structure with a fictitious permittivity. This system exhibits a non trivial and quite complex behavior because of the induced diffraction grating.