Monday, October 7

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Poster Session 1

P1.1: Progress in development of an ultrafast power-scalable long-wave infrared parametric source

X. Xiao, H. Huang, W. Du, J. Nees, A. Galvanauskasb, I. Jovanovic, University of Michigan (United States)

Abstract
Ultrabroadband optical parametric chirped-pulse amplification (OPCPA) is a promising route for generation of highenergy ultrafast optical pulses in the long-wave infrared (LWIR) regime from all solid-state sources. We discuss the progress in developing a new power-scalable LWIR OPCPA architecture based upon high-power mid-infrared nanosecond pumping at 2.7 μm, which can be provided by Er:ZBLAN fiber lasers. It is shown through numerical simulation that a design based on OPCPA in GaSe crystals could access the few-cycle operating regime. The experimental progress on Er:ZBLAN fiber laser and surrogate pump pulse generation is described, where 2.7-μm nanosecond pulses were produced using cascaded optical parametric oscillation and amplification in KTA crystals. We also discuss the experimental progress in the production of broadband seed pulses in an AGS crystal through chirped-pulse difference-frequency generation driven by a Ti:sapphire laser, where seed pulses centered near 10 μm were demonstrated. These preliminary results represent the foundation for continued LWIR source development based upon this architecture.

P1.2: Tunable ultrafast Yb-fiber laser for efficient seeding of cryogenic Yb:YLF amplifiers

Y. Hua, Y. Liu, U. Demirbas, M. Pergament, F. Kärtner, DESY (Germany)

Abstract
We present a compact and efficient Ytterbium-fiber-based ultrafast laser system that provides tunable output spectra centered either around 995 nm or 1020 nm via a pre-chirp managed nonlinear amplification scheme. The central wavelengths of the generated pulses match the two distinct emission peaks of Yb:YLF gain media at cryogenic temperatures (995 & 1020 nm), making this source an ideal and flexible front-end laser seed system for cryogenically-cooled Yb:YLF amplifiers. For both central wavelengths, pulse energies approaching 10 nJ, and spectral bandwidth above 4-nm have been achieved. We believe that usage of this seed source could potentially enable generation of sub-500-fs long pulses with multi-100 mJ-level energies in the following cryogenic Yb:YLF amplifier chain.

 

P1.3: Large-aperture CO2 amplifiers for mid-IR picosecond laser system

H. M. von Bergmann, Laser Research Institute (South Africa); F. Morkel, PaR Systems, (Pty) Ltd (South Africa); R. Mulder, PaR Systems (South Africa)

Abstract
A large-aperture, high-pressure, transversely excited CO2 laser with large discharge x-section of 22×22 mm2 and gain length of 800 mm has been developed. The laser will be employed as multi-pass or final amplifier in multi-TW, mid-infrared ps laser systems emitting at a wavelength of 10 μm. The self-contained amplifier operates reliably at gas pressures of up to 12 bar and provides stable discharges with a small signal gain of >3 %/cm. Development and design of the amplifier will be described and measured performance characteristics will be presented. Further scaling of the high-pressure amplifier to high repetition rates and discharge x-sections>40×40 mm2 is being investigated and preliminary results obtained with an experimental test system will be reported.

 

P1.4: Simulation of Gain Narrowing for Near-Infrared Ultrashort Pulses

R. Springer,C. Pflaum, Friedrich-Alexander-Univ Erlangen-Nürnberg (Germany)

Abstract
Within this work, a novel chromatic amplification model for ultrashort pulses is presented. By performing a modified Wigner transform including the Kaiser window function, a time-frequency correlation is obtained that contains only positive values. The positive value range enables the physical correct amplification and propagation of the Wigner distribution in gain media with nonlinear gain bandwidth. To demonstrate the applicability to ultrashort pulses, the presented model is used to simulate a Ho:YAG regenerative amplifier. In this particular example, pulses with a spectral range of 30 nm are seeded into the cavity and amplified from the nanojoule to the millijoule level. As a result of the proposed modeling technique, pulse energy and spectral changes during amplification could be precisely calculated. The simulated results are in well agreement with experimental measurements.

 

P1.5: Nonlinear pulse compression of OPCPA at 1.55 ¬µm by multiple plate continuum

M.-W. Lin,National Tsing Hua University (Taiwan); C. Tsai, Y. Tseng, National Tsing Hua University/Institute of Photonics Technologies (Taiwan); A. Liang, National Tsing Hua University/ Institute of Photonics Technologies (Taiwan); S. Yang, M. Chen, National Tsing Hua University/Institute of Photonics Technologies (Taiwan)

Abstract
Nonlinear pulse compression is demonstrated using 0.7-mJ, 80-fs, 1.55-μm pulses generated from an optical parametric chirped-pulse amplification system. By focusing the pulses into 9 pieces, 200-μm-thick quartz plates, the involved multiple plate continuum generation and the subsequent pulse compression using a Fourier pulse shaper can ultimately produce pulses with a nearly transform-limited duration of 20 fs.

 

P1.6: Second harmonic generation in lithium triborate with temperature gradients

P. Dansette, EKSPLA (Lithuania) and Laboratory for fundamental BioPhotonics (LBP), École Polytechnique Fédérale de Lausanne (EPFL) (Switzerland); M. Eremchev, Laboratory for fundamental BioPhotonics (LBP), École Polytechnique Fédérale de Lausanne (EPFL) (Switzerland); A. Michailovas, EKSPLA (Lithuania) and Center for Physical Sciences and Technology (Lithuania)

Abstract
Frequency doubling of stretched pulses can be advantageous when using quasi-phase matching crystals with a linearly chirped period. We propose a similar solution using a bulk lithium triborate crystal with a linear temperature gradient. Unlike the chirp of a periodically poled crystal, the temperature gradient can be easily varied to optimize the second harmonic properties. We demonstrate, through both simulation and experiment, that such a temperature gradient can improve not only second harmonic conversion efficiency, but also the beam quality and either increase the bandwidth or shorten the pulse duration of the second harmonic radiation at the output of the crystal.

 

P1.7: Filamentation and supercontinuum generation in polycrystalline strontium barium niobate (SBN) using infrared femtosecond laser pulses

R. Šuminas, N. Garejev, A. Marcinkevičiūtė, V. Jukna, G. Tamošauskas, A. Dubietis, Vilnius University (Lithuania)

Abstract
We demonstrate broadband supercontinuum generation in polycrystalline strontium barium niobate using infrared femtosecond laser pulses in the regimes of normal, zero and anomalous group velocity dispersion. The characteristic properties of polycrystalline strontium barium niobate allow us to observe off-axis second harmonic generation, which provides a simple and straightforward way to visualize filamentation dynamics and to determine the nonlinear refractive index of the material.

 

P1.8: Influence of color centers on filamentation and supercontinuum generation in alkali metal halides NaCl and KBr

A. Marcinkevičiūtė, V. Jukna, R. Šuminas, N. Garejev, G. Tamošauskas, A. Dubietis, Vilnius University (Lithuania)

Abstract
We report on supercontinuum generation with femtosecond mid-infrared laser pulses in 5 mm-thick alkali metal halide (NaCl and KBr) samples. Multi-octave supercontinuum spectra (in the range of 0.85-5.2 μm and 0.9-5.2 μm in NaCl and KBr, respectively) are produced by filamentation of 70 fs and 3.6 μm input pulses in continuously translated samples, while in the static setup the width of supercontinuum spectra readily decreases due to rapid formation of color centers. We show that the influence of color centers on the supercontinuum spectrum can be simulated numerically by using a simple phenomenological model considering color centers as impurities with a certain energy bandgap.

 

P1.9: Considerations in modelling supercontinuum in bulk and numerical investigation of the stability of highly nonlinear processes

A. Špacek, J. T. Green, L. Indra, J. Novák, F. Batysta, P. Bakule, B. Rus, ELI Beamlines (Czech Republic)

Abstract
We discuss the implementation of a 3D numerical model capable of simulating filamentation and supercontinuum generation by solving the propagation equation for ultrashort pulses. There are many different ways for implementing such numerical model. The usual method is to solve a unidirectional propagation equation. The equation used in our model will be presented in detail and we will discuss important considerations when implementing such model. Making valid approximations in the nonlinear driving terms is especially important to improve the speed of the calculation and allow extensive simulation scans over a broad parameter space. We will discuss the validity of these approximations when calculating the plasma density and ionization rates, and we will compare them to the ones commonly used in the field. Furthermore, we will present our methods of improving the performance of our code.

The numerical model is then used to investigate the behavior of the supercontinuum with varying input parameters and identify the conditions under which the supercontinuum can be of suitable stability for applications. The aim of these simulations is to explain the stability of the supercontinuum measured at ELI-Beamlines for picosecond driving pulses in a YAG crystal. We also examine a passive method of stabilizing the peak intensity of input pulses and the effect of using these stabilized pulses as pump for supercontinuum generation.

 

P1.10: Femtosecond infrared synchronously pumped optical parametric oscillator based on PPKTP crystal

I. Pipinyte, J. Vengelis, V. Tamulienė, Vilnius University (Lithuania); R. Grigonis, Vilnius University (Lithuania) and Light Conversion (Lithuania); V. Sirutkaitis, Vilnius University (Lithuania)

Abstract
We present results obtained during investigation of synchronously pumped optical parametric oscillator (SPOPO) pumped by femtosecond Yb:KGW laser (1.03 μm) with several different output couplers and focusing lenses. The periodically poled potassium titanyl phosphate crystal (PPKTP) was used as the nonlinear medium for parametric generation. The obtained efficiency of the maximum parametric light conversion to signal power was more than 40% at 1516 nm wavelength, whereas the achieved continuous tuning range of the signal was 1490 nm – 1820 nm with signal pulse durations ranging from 90 fs to 330 fs.

 

P1.11: Design and demonstration of Thomson scattering laser architecture for generation of quasi-monoenergetic gamma photons at multi-kHz

M. WhittleseyS. Chen, University of Michigan (United States); C. Geddes, Lawrence Berkeley National Lab (United States); A. Galvanauskas, University of Michigan (United States)

Abstract
In order to generate quasi-monoenergetic gamma photons, a laser source is needed that provides 1 ps – 10 ps flat-top and bandwidth-limited pulses with multi-kW average power and multi-J pulse energy. Utilizing spatial, temporal, and spectral combination, we are proposing a power and energy scalable system architecture for coherently synthesizing the prescribed pulse profiles. We report a proof-of-principle experimental validation of this laser architecture, which includes demonstrating optical systems for simultaneous pulse stretching and spectral shaping/slicing, simultaneous pulse compression and spectral combination, producing the correct spectral profile for synthesizing flat-top bandwidth-limited pulses, and design of control techniques for implementing coherent time-domain pulse synthesis. Experimental work on completing time-domain synthesis and stabilization is in progress.

 

P1.12: High-accuracy single-shot CEP noise measurement at arbitrary repetition rate

M. Kurucz,ELI-ALPS (Hungary); S. Toth, ELI-ALPS (Hungary) and University of Szeged (Hungary); R. Flender, L. Haizer, B. Kiss, ELI-ALPS (Hungary); B. Perseille, E. Cormier, CELIA, Université de Bordeaux – CNRS – CEA (France)

Abstract
The TOUCAN method is an arbitrary repetition rate single-shot CEP drift measurement technique based on dispersive Fourier transformation and has been experimentally tested at 100 kHz. TOUCAN was validated by a direct comparison with an independent traditional CEP drift measurement technique. The impact of a temporal jitter on the measurement is investigated and a new mitigation technique is shown to produce high accuracy jitter-free CEP noise extraction.

 

P1.13

Self-referenced carrier-envelope phase stabilization of Er:Yb:glass lasers

R. Lemons, Colorado School of Mines (United States) and SLAC National Accelerator Laboratory (United States); W. Liu, I. Fernandez de Fuentes, S. Droste, SLAC National Accelerator Laboratory (United States); G. Steinmeyer, Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (Germany); C. G. Durfee III, Colorado School of Mines (United States); S. Carbajo, SLAC National Accelerator Laboratory (United States)

Abstract
We present ultralow jitter carrier-envelope phase (CEP) stabilization of a SESAM modelocked Er:Yb:glass laser at 1.55 μm via the feed-forward method using an acousto-optic frequency shifter (AOFS). We demonstrate jitter stabilization of 2.9 as (3.5 mrad over 1 Hz – 3 MHz) and long-term stabilization over a period of eight hours.

 

P1.14: Single cavity dual-comb generation from a polarization-maintaining nonlinear-amplifying-loop-mirror modelocked dual-color Yb:fiber laser

J. Fellinger, A. S. Mayer, G. Winkler, University of Vienna (Austria); S. Droste, C. Li, C. M. Heyl, I. Hartl, Deutsches Elektronen-Synchrotron DESY (Germany); O. H. Heckl, University of Vienna (Austria)

Abstract
We demonstrate for the first time the generation of a dual-comb from a single all-polarization-maintaining ytterbium (Yb)-fiber laser via spectral subdivision using a tunable mechanical filter. The laser emits two pulse trains (centered around 1030 nm and 1060 nm respectively) with repetition rates that differ by 2.5 kHz around a nominal repetition rate of 77 MHz. Spectral overlap is achieved outside of the cavity by amplifying the 1030-nm pulse train and broadening it in a nonlinear fiber. Subsequently, spatial overlapping generates a down-converted radio frequency comb. The usability of this dual-comb setup is demonstrated by measuring the transmission of a 5-mm thick zinc selenide (ZnSe) etalon while the laser is completely free-running.

 

P1.15: Extraction and amplification of an optical comb line using an auxiliary continuous-wave laser in a feedforward scheme

P. Brochard, Université de Neuchâtel (Switzerland); B. Rudin, F. Emaury, Menhir Photonics AG (Switzerland); V. Wittwer, S. Schilt, T. Südmeyer, Université de Neuchâtel (Switzerland)

Abstract
We present a simple method based on a feedforward scheme to extract and amplify a single line of a frequency comb spectrum from a mode-locked laser that is straightforwardly applicable to arbitrary comb mode spacing. This is a benefit compared to previously reported approaches relying on optical injection locking of an auxiliary laser by the selected comb line, which becomes challenging for low repetition rate combs. The proposed method consists in transferring the frequency noise properties and stability of the selected comb line to an auxiliary laser using a feedforward scheme. The heterodyne beat signal between the laser and the comb mode is used as a driving signal in an acousto-optic modulator that shifts the frequency of the auxiliary laser while removing the laser noise. We present a proof-of-principle demonstration of this method using low-noise mode-locked lasers with different repetition rates. We show a faithful transfer of the comb noise to the auxiliary laser, which is equivalent to isolating and amplifying this comb line. The amplification factor is typically 20-30 dB. We present a detailed noise analysis and discuss the present limitations of the method.

 

P1.16: Generation of intense single-cycle pulse in the air based on all solid state system (WITHDRAWN)

M. Seo, Max Planck POSTECH/Korea Research Initiative (Korea)

Abstract
Generation of intense single-cycle pulses is demonstrated in the air, using a compact double-stage of multiple thin solid plates. Dispersion control between each stage gives symmetric spectral broadening as a result of self-phase modulation. The conversion efficiency from input pulses to the final continuum was optimized to be as 70% by adjusting beam size between each stage, minimizing energy loss. Pre and post compressions are done by optimizing dazzler parameters and set of chirped mirrors. As a result, octave-spanning spectrum, covering from 405 nm to 985 nm, has been generated at the -20 dB intensity level which supports transform-limited pulse duration down to 2.41 fs while maintaining good beam quality with long-term power stability. Generated intense broadband supercontinuum can be used not only to generate bright isolated attosecond pulses but also tool for exploration of other ultrafast phenomena.

 

P1.17: Nonlinearly compressed CEP-stable YDFA delivering 60 ŒºJ, 80 fs at 1030 nm

M. Natile,Amplitude Laser Group (France) and LIDYL, CEA Saclay (France); A. Golinelli, Laboratoire Charles Fabry (France); F. Guichard, Amplitude Laser Group (France); M. Hanna, Laboratoire Charles Fabry (France); Y. Zaouter, Amplitude Laser Group (France); R. Chiche, Laboratoire de l’Accélérateur Linéaire, IN2P3 (France); X. Chen, Amplitude Laser Group (France); J. Hergott, W. Boutu, LIDYL (France); P. Georges, Laboratoire Charles Fabry (France)

Abstract
We report on the CEP stabilization of a nonlinearly compressed Yb-doped fiber amplifier delivering 60 μJ-pulses, 80 fs of duration at 100 kHz. The stabilization setup relies on a hybrid technique where a passively stabilized Yb-doped fiber based CEPstable front-end (FE) seeds a rod-type chirped pulse Yb-doped fiber amplifier (FCPA) and a multi-pass compression cell. The amplified signal is actively CEP-stabilized acting on an integrated Electro-Optical-Modulator (EOM). The CEP stability of the system has been characterized using a f-2f setup and different detection techniques. A short-term stability of the system measured every shot at the full laser repetition rate shows a CEP noise lower than 325 mrad over 1 s. The long-term stability is 375 mrad single shot over 66 minutes at 10 kHz. The CEP-stable FCPA followed by a nonlinear compression stage opens the way for high repetition rate HHG applications for atto-science.

 

P1.18: Investigation of the Noise Properties of the Offset Frequency in a Quantum Cascade Laser Frequency Comb

A. Shehzad,P. Brochard, R. Matthey, University of Neuchâtel (Switzerland); F. Kapsalidis, M. Shahmohammadi, M. Beck, ETH Zurich (Switzerland); A. Hugi, P. Jouy, IRsweep SA (Switzerland); J. Faist, ETH Zurich (Switzerland); S. Thomas, S. Schilt, University of Neuchâtel (Switzerland)

Abstract
The generation of frequency combs in the mid-infrared (MIR) spectral region by quantum cascade lasers (QCLs) has the potential for revolutionizing dual-comb multi-heterodyne spectroscopy in the molecular fingerprint region. However, in contrast to frequency combs based on passively mode-locked ultrafast lasers, their operation relies on four-wave mixing in the semiconductor gain medium, and so far, no direct self-referencing has been achieved. We present a detailed frequency noise characterization of a MIR QCL frequency comb operating at 7.4-GHz mode spacing. Using a beat measurement with a narrow-linewidth single-mode QCL in combination with a dedicated electrical scheme, we measured the frequency noise properties of an optical mode of the QCL-comb, and indirectly of its offset frequency for the first time, without detecting it by the standard approach of nonlinear interferometry used with ultrafast mode-locked lasers, in addition to the separate measurement of its mode spacing. We observed a strong anti-correlation between the frequency fluctuations of the indirect offset frequency signal and of the mode spacing, leading to optical modes with a linewidth below 1 MHz in the free-running QCL-comb (at 1-s integration time), much narrower than the individual contributions of the offset frequency and mode spacing that amount to a few MHz each. The observed behavior is similar to a diode-pumped solid-state mode-locked laser operating at 1.5 µm with a high repetition rate of 25 GHz that we evaluated with the same approach.

 

P1.19: Phase Stabilization in a Sub-Cycle Parametric Waveform Synthesizer

R. E. Mainz, CFEL at DESY (Germany); G. Rossi, F. Scheiba, Y. Yang, M. Silva Toledo, G. Cirmi, F. X. Kaertner, Center for Free-Electron Laser Science (Germany)

Abstract
An all in-line multi-phase detector allows to fully stabilize and control the optical waveform generated by a multichannel, multi-stage parallel parametric waveform synthesiyzer at the experimental point. Stable HHG continuous spectra proof the short and long term stability of the synthesized waveform.

 

P1.20: Achieving extreme light intensities using optically-curved plasma mirrors

H. Vincenti, CEA Saclay (France)

Abstract
Achieving a light source delivering intensities up to the Schwinger limit of 1029W/cm2 would allow exploring novel regimes of strong-field Quantum ElectroDynamics (QED) where vacuum would be ripped apart. A promising candidate to build such a light source would be to find a realistic implementation of the Curved Relativistic Mirror (CRM) concept which consists in: (i) inducing a Doppler upshift and temporal compression of a counter-propagating incident laser (ii) focusing the upshifted radiation down to a focal spot size much smaller than the one possible with the incident laser. Since its emergence in 2003, many implementations of the CRM concept were proposed. However, none has led to a detailed and feasible experimental proposal, mainly because they make use of idealized experimental conditions that are either not realistic or beyond present experimental know-how. In this context, we propose a novel and realistic all-optical scheme to implement the CRM concept using so-called relativistic ‘Plasma Mirrors’ (PM) formed when an ultra-intense laser with high-contrast is focused on an initially-flat solid target. In this scheme, the PM surface is optically curved, either by radiation pressure or using secondary pre-pulse beams. As we demonstrate, this enables a considerably higher control of the PM shape than the one obtained with all other schemes proposed so far relying on the use of preshaped solid targets, which are beyond present State-Of-The-Art of manufacturing techniques. Besides and as opposed to previous implementations, our new scheme is validated using cutting-edge 3D PIC simulations at an unprecedented scale using the pseudo-spectral 3D PIC code WARP+PICSAR. These simulations show that intensities between 1025W/cm2 and up to 1028W/cm2 can be achieved with a 3PW laser. The very high robustness of this scheme to potential laser/plasma defects and its feasibility are demonstrated by inputting the measured spatio-temporal profile (amplitude and phase) of the BELLA PW laser in PIC simulations. To account for the QED effects occurring at such intensities, novel QED modules have been added in the code and will be discussed here. These modules will be essential to find clear signatures of the intensities achieved in experiments. As our scheme is achievable with current experimental know-how on a multi-PW laser, it should soon become a game-changer in high field Science.

 

P1.21: Five-fold compression of 250 TW laser pulses

E. A. Khazanov,V. Ginzburg, I. Yakovlev, A. Zuev, A. Korobeinikova, A. Kochetkov, A. Kuzmin, S. Mironov, A. Shaykin, I. Shaikin, Institute of Applied Physics (Russian Federation)

Abstract
The pulse spectrum at the laser output was stretched due to self-phase modulation in glass and then compressed by chirping mirrors. It was demonstrated that with an optimal choice of mirror dispersion, a pulse with an energy of 17 J can be compressed from 70 fs to 14 fs. The method has three undoubted merits: simplicity and low cost, negligible pulse energy loss, and applicability to any high-power laser.

 

P1.22: Technical Aspects of Generating Intense Few-Cycle Pulses in the Long-Wave Infrared

D. Wilson, Advanced Laser Light Source and few-cycle inc., Institut Nationale de la Recherche Scientifique (Canada); A. Summers, S. Zigo, J. R. Macdonald Laboratory, Department of Physics, Kansas State University (United States); B. Davis, Department of Physics, University of Connecticut (United States); S. Robatjazi, J. A. Powell, D. Rolles, A. Rudenko, J. R. Macdonald Laboratory, Department of Physics, Kansas State University (United States); C. A. Trallero-Herrero, Department of Physics, University of Connecticut (United States)

Abstract
We present technical aspects of generating intense fields in the long-wave infrared using the method of difference frequency generation. The laser source delivers fields with tunable central wavelengths from 5 to 9 micron with peak powers greater than 1 Gigawatt at a repetition rate of 1 kHz. We have demonstrated peak intensities greater than 10 TW/cm2 with this source by observing strong-field ionization of xenon from its ground state from the entire tunable range.

 

P1.23: The current commissioning results of the Allegra kilohertz ultra-fast high-energy laser system at ELI-Beamlines

J. Novák,R. Antipenkov, ELI Beamlines (Czech Republic); F. Batysta, ELI Beamlines (Czech Republic) and Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering (Czech Republic); R. Boge, ELI Beamlines (Czech Republic); E. C. Erdman, Charles University, Faculty of Mathematics and Physics (Czech Republic) and ELI Beamlines (Czech Republic); M. Greco, J. T. Green, B. Himmel, M. Horáček, ELI Beamlines (Czech Republic); Z. Hubka, L. Indra, ELI Beamlines (Czech Republic) and Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering (Czech Republic); K. Majer, T. Mazanec, P. Mazůrek, J. A. Naylon, V. Šobr, ELI Beamlines (Czech Republic); A. Špaček, ELI Beamlines (Czech Republic) and Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering (Czech Republic); P. Strkula, M. Torun, B. Tykalewicz, P. bakule, B. Rus, ELI Beamlines (Czech Republic)

Abstract
The Allegra laser system is designed to provide sub-20 fs pulses with tens of mJ of energy with exceptionally high contrast at a 1 kHz repetition rate. It is the main driver for high harmonic and plasma X-ray secondary sources at ELI-Beamlines facility. The system is based on 7 stages of picosecond OPCPA pumped by 5 Yb:YAG thin-disk picosecond lasers and has been already commissioned at a preliminary energy level of 30 mJ and compressed by 90 % efficient chirped mirror compressor to less than 15 fs. Even at this 30 mJ preliminary energy, Allegra has been successfully used to drive a high harmonic generation experiment. In this paper, we present an overview of Allegra system and the current state of deployment with an outline of the path towards an output energy of 50 mJ and above.

 

P1.24: All solid-state intra-pulse Raman shifting of high-power 1 µm, microjoule-level femtosecond pulses at multi-megahertz repetition rate (WITHDRAWN)

K. Fritsch, Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg (Germany) and Ludwig-Maximilians- Universität München (Germany); S. Gröbmeyer, Ludwig-Maximilians-Univ München (Germany); M. Poetzlberger, Max-Planck-Institut für Quantenoptik (Germany); K. Mak, Ludwig-Maximilians-Univ München (Germany); F. Krausz, Ludwig-Maximilians-Univ München (Germany) and Max-Planck-Institut für Quantenoptik (Germany); J. Brons, TRUMPF Laser GmbH (Germany) and Ludwig-Maximilians-Universität München (Germany); O. Pronin, Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg (Germany) and Max-Planck-Institut für Quantenoptik (Germany)

Abstract
We show first experimental evidence as well as numerical calculations for soliton Raman self-frequency shifting in a Herriott-type multi-pass cell. The system is driven by a nonlinearly spectrally broadened and compressed high-power Yb:YAG thindisk laser system delivering 70 W, 16 fs and 2.5 μJ pulses. This first demonstration holds promise for realization of all-solid-state compact, efficient power scalable Raman shifters pumped by well-established 1 μm femtosecond laser sources.

 

P1.25: Thermal investigation of nonlinear crystals for high power ultrashort MID-IR OPCPA pumped at 1μm

M. Namboodiri, Deutsches Elektronen-Synchrotron DESY (Germany); T. Golz, J. H. Buß, I. Grguraš, M. Schulz, R. Riedel, Class 5 Photonics GmbH (Germany); T. Laarmann,  Deutsches Elektronen-Synchrotron DESY/The Hamburg Centre for Ultrafast Imaging CUI (Germany); M. J. Prandolini, Class 5 Photonics GmbH (Germany)

Abstract
The aim of the present study is to understand the limiting factors due to high thermal load when high power levels and high intensity are present inside infrared nonlinear crystals (NLCs).

 

P1.26: High average power modelocked thin-disk lasers: nonlinearity management and power scaling to 350 W

F. Saltarelli, I. Graumann, L. Lang, ETH Zurich (Switzerland); D. Bauer, TRUMPF Laser GmbH (Germany); C. R. Phillips, U. Keller, ETH Zurich (Switzerland)

Abstract
Modelocked thin-disk lasers (TDL) oscillators are interesting sources for compact table-top generation of femtosecond pulses with high average power and megahertz repetition rates. Scaling these oscillators beyond 300 W has been elusive for several years, due to various experimental constraints. Here we present scaling guidelines to overcome these constraints, and show our latest TDL result so obtained. Our new laser produces 940 fs pulses at 1030 nm at 8.8 MHz repetition rate, with an average power of 350 W, which is a record for modelocked oscillators.

 

P1.27: Free-propagating femtosecond laser filamentation for standoff excitation of uranium

M. Burger,P. Skrodzki, L. Finney, J. Nees, I. Jovanovic, University of Michigan (United States)

Abstract
Laser-based techniques and particularly ultrafast high-power lasers can be effectively utilized to address many challenges associated with nuclear safety and security. Detection of uranium over long distances presents one such challenge. By optimizing the beam dispersion, we demonstrate that the free-propagating ultrafast laser filaments can induce uranium plasma emission from 10-m range in laboratory environment. The results show promise towards significantly extending the excitation range, and thus improving diagnostics and analytical capabilities in ultrafast laser-induced breakdown spectroscopy of high-Z elements.

 

P1.28

Elemental LIBS analysis of wheat samples using nJ femtosecond laser

I. Plavšin, Agricultural Institute Osijek (Croatia) and Centre of Excellence for Biodiversity and Molecular Plant Breeding, University of Zagreb, Faculty of Agriculture, Zagreb (Croatia); M. Ivić, Agricultural Institute Osijek (Croatia); D. Novoselović, Agricultural Institute Osijek (Croatia) and Centre of Excellence for Biodiversity and Molecular Plant Breeding, University of Zagreb (Croatia); B. Resan, University of Applied Sciences and Arts Nortwestern Switzerland (Switzerland)

Abstract
In agriculture, elemental plant analysis is one of the most important steps towards efficient crop production. The information obtained through elemental analyses are a useful guide for crop producers and breeders how to estimate nutritional status and improve fertilizer effectiveness in plants, stress resistance, quality of crops and crop products, and developing diseases. Currently available analytical methods involve complex and extensive sample preparation which usually makes them time-consuming and expensive. One of the most attractive alternative analytical methods that allows rapid, in-situ and multi-elemental analysis is laserinduced breakdown spectroscopy (LIBS). In this experiment we demonstrated the potential of femtosecond pulse, MHz pulse repetition rate, nJ pulse energy level, LIBS (fs-nJ-LIBS) for the determination of elements in wheat. The laser generated 160 fs pulses, with 30 nJ energy, 80 MHz pulse repetition rate, and centered spectrum at 1030 nm. In obtained spectra, we identified chemical elements in our sample. We are working on setup improvements to increase the signal-to-noise ratio in order to enable elemental concentration determination from fs-nJ-LIBS spectra.

 

P1.29: Selective ablation of ultrathin aluminium film on silicon substrate using ultrashort pulse laser radiation

L. Pabst, R. Ebert, H. Exner, Laserinstitute Hochschule Mittweida (Germany)

Abstract
The selective structuring of 30 nm thin aluminium films on silicon wafers with a 100 nm silicon dioxide layer was investigated using ultrashort pulsed laser radiation (l = 1028 nm, tp = 0.2 – 10 ps, w86 = 15 μm). The influence of the processing parameters such as pulse duration, fluence, pulse number and scan speed was investigated. With increasing pulse duration the ablation threshold of the 30 nm aluminium thin film decreased. Whereas, the damage threshold of the substrate material increased with increasing pulse duration. Therefore, the processing window for complete ablation of the 30 nm aluminium film without damaging the underlying silicon oxide increased with increasing pulse duration. The processing window for selective ablation of thin films on absorbing substrates was comparative small compared to none absorbing substrates, like glass. Due to fact that the ablation thresholds were in the same order of magnitude for the aluminium thin film and the substrate material. A suitable selection of the pulse duration could significantly increase the processing window. Therefore, the pulse duration was an important processing parameter not only influencing the ablation quality but also to achieve a selective ablation of the thin film.

 

P1.30: Time resolved few cycle pulse laser damage/ablation of thin film coatings

E. A. Chowdhury, N. Talisa, A. AlShafey, B. Harris, Ohio State Univ (United States); A. Davenport, E. Randell, Colorado State University (United States); C. S. Menoni, Colorado State University (United States) and Colorado State University (United States)

Abstract
With the push to approach Schwinger’s Limit with exa-watt class lasers, energy constraints necessitates going to shorter and shorter pulses with highest possible energies. This type of architecture requires ultra-broad band mirrors to operate at very high intensities (>1014 Wcm-2), or fluences > 1 J/cm2. Current state of the art optics have to operate well below an order of magnitude of these fluence/intensities. So, to approach exawatt peak power this way requires us to study the fundamental physical mechanisms of few cycle pulse laser induced damage of thin films interference coatings in a systematic way, to pave the pathway for development of high damage threshold few cycle optics. Here we report time resolved surface microscopy study of few cycle pulse laser induced damage and ablation of one, two and four layer thin film interference coatings, and compare how their damage and ablation dynamics differ from few cycle pulse regime (< 10 fs) and longer pulse (110 fs) regime.