Tuesday, October 8

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Poster Session 2

 

P2.1: A phase-only pulse shaper for multi-octave light sources

N. Forget, S. Bux, Fastlite (France); V. M. di Pietro, Fastlite (France) and Institut de Physique de Nice (France); U. Bortolozzo, S. Residori, A. Jullien, Institut de Physique de Nice (France)

Abstract
Continuous spectral phase shaping is demonstrated over a spectral bandwidth of 450 THz, spanning from 540 nm to 2500 nm. The spectral and dynamic ranges of the shaper are large enough to significantly shape single-cycle pulses or even transient electric fields in the near infrared.

 

P2.2: Temporal characterization of laser pulses in a multi-octave wavelength range

W. Cho, Gwangju Institute of Science and Technology (Korea, Republic of); K. Kim,S. Hwang, Institute for Basic Science (Korea)

Abstract
We demonstrate the temporal characterization of laser pulses using a method called the tunneling ionization with a perturbation for the time-domain observation of an electric field (TIPTOE). The TIPTOE method can be generally applied for a broad wavelength range from UV to IR. Since it utilizes extreme nonlinearity of ionization, it requires a certain amount of pulse energy to induce ionization. In this work, we estimate the required pulse energy for various gaseous targets. We calculate the total ionization yield by solving time dependent Schrodinger equation for Ar, O2, Xe, and difluoroethane. It is found that the required pulse energy for the TIPTOE measurement can be greatly reduced by using low-ionization-potential gases. Therefore, the use of the low ionization potential gas will extend the applicability of the TIPTOE methods even for low power laser systems.

 

P2.3: Removal of time smearing artifact in PG FROG

D. J. Kane, Mesa Photonics LLC (United States); N. Hartmann, R. N. Coffee, A. R. Fry, SLAC National Accelerator Laboratory (United States)

Abstract
Time smearing can be a large problem in polarization-gate frequency-resolved optical gating (PG-FROG) measurements because the signal travels in the same direction as the probe beam. Large time windows in single-shot pulse measurements requiring large crossing angles exacerbate the problem. In this work, we experimentally demonstrate that by using a blind-FROG algorithm, the time smearing can be localized to the gate by independently measuring the gate pulse. As a result, when using an X-FROG algorithm with a PG X-FROG trace, care must be taken when using an independent measurement of the gate in the X-FROG algorithm.

 

P2.4: Third-generation pulse characterization with FROG and d-scan

E. R. Escoto, MBI für Nichtlineare Optik und Kurzzeitspektroskopie (Germany); D. Gerth, Chemnitz University of Technology (Germany); R. Jafari, R. Trebino, Georgia Institute of Technology (United States); B. Hofmann, Chemnitz University of Technology (Germany); G. Steinmeyer, MBI für Nichtlineare Optik und Kurzzeitspektroskopie (Germany)

Abstract
Multi-shot pulse-measurement techniques, when used to characterize an unstable pulse train, usually exhibit what is known as the coherent artifact. Failing to detect and account for this artifact may lead to erroneous results. It therefore appears mandatory to understand the response of a pulse characterization technique in the presence of pulse instability. Modifying the respective retrieval algorithms, we propose strategies not only to detect but also to measure the instability of a pulse train using FROG and d-scan. Without requiring any additional measurements, our novel retrieval methods can be readily adapted to working experimental setups and completely assess average pulse characteristics of an unstable pulse train.

 

P2.5: 100% reliable frequency-resolved optical gating pulse retrieval algorithmic approach

R. Jafari,T. Jones, R. Trebino, Georgia Institute of Technology (United States)

Abstract
We introduce a new, highly reliable algorithmic approach for the reconstruction of ultrashort pulses from frequencyresolved optical gating (FROG) traces. Our approach involves the direct retrieval of the spectrum of the pulse from the marginal(s) of the FROG trace and uses it for initial guesses for the generalized-projections pulse-retrieval algorithm. Using a dozen or so initial guesses, the algorithm begins with a smaller, coarser version of the trace and only uses the best results for the next larger trace and eventually on the full trace (when only a few iterations are required). We implemented this approach for the most frequently used geometries of FROG: second-harmonic generation (SHG), polarization gate (PG), and two of the variants of the transient grating (TG). We tested it on more than 50,000 simulated pulses with even very high complexities and achieved 100% convergence (zero stagnations). We call this the retrieved amplitude N-grid algorithmic (RANA) approach.

 

P2.6: Characterization of measurement devices for temporal laser pulse contrast with high dynamic range

S. Bock, T. Pueschel, F. Herrmann, J. Loetfering, R. Gebhardt, U. Helbig, U. Schramm, Helmholtz-Zentrum Dresden-Rossendorf eV (Germany)

Abstract
We demonstrate a protocol for the absolute calibration of third-order autocorrelator (TO-AC) response to the temporal profile of a high contrast high power laser pulse based on either artificially generated coherent pre- and post-pulses or incoherent background. The dynamic range provided by the protocol exceeds more than eight orders of magnitude. For cross-calibration, the technique of self-referenced spectral interferometry with extended time excursion (SRSI-ETE) is used.

 

P2.7: Simple and sensitive intensity-and-phase pulse measurement

T. Jones,Georgia Institute of Technology (United States); P. Šušnjar, R. Petkovšek, University of Ljubljana (Slovenia); R. Trebino, Georgia Institute of Technology (United States)

Abstract
Important light in need of measurement is also often of low intensity. And while there are existing techniques that can measure weak pulses, some of them are not self-referenced, and another requires an aperiodically poled LiNiO3 waveguide, which can be both expensive to obtain and difficult to work with in practice. Others involve complex apparatuses or expensive electronics (>$100,000), and still others cannot discern a stable train of short simple pulses from and unstable train of longer more complex ones. For these reasons, it has not been possible to reliably and practically measure the complete intensity and phase of very weak (~10fJ), relatively long (~10ps) pulses. In this submission, we present a practical, self-referenced, frequency-resolved-optical-gating technique for measuring picosecond pulses with few-femtojoule-level energies. We experimentally demonstrate the capabilities of this technique by measuring complex pulses at high and low energies as weak as 24fJ.

 

P2.8: High vacuum compatible wave front sensor for focal spot diagnostics and optimization

L. Doudet, B. Wattellier, PHASICS SA (France); L. Meignien, LULI (France)

Abstract
Experiments done on laser facilities require a perfect control of the focal spot quality, location and stability at the target level. It is then mandatory to characterize and optimize the laser at the target level as close as possible to the actual laser-matter experimental conditions. In other words, it is necessary to measure under high vacuum conditions, a beam focused by a high numerical aperture off-axis parabola to reach the highest intensity. The best solution is to measure the diverging beam with a wave front sensor located directly after the focus without any relay optics. To bring solution to this problematic, we developed a high vacuum compatible wave front sensor which is able to drive an adaptive optics loop on a diverging beam up to f/2 directly from the interaction chamber center. We studied the impact of these specific conditions on wave front measurement such as limited heat dissipation, mechanical stress. We also show how we controlled those constrained and obtained the same performance in vacuum than in standard pressure conditions.

 

P2.9: Millisecond optical guiding in the wake of 800- and 400-nm ultrafast laser-driven filaments

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

Abstract
We demonstrate millisecond (ms)-scale guiding of near-infrared beams in the wake of 800- and 400-nm ultrafast laserdriven filaments formed in air. For the same pulse energy, the 400-nm driving laser wavelength produces filaments that confine the beam guiding to a single spot over a longer distance than the 800-nm wavelength. The guided mode exhibits a single-spot, circular radial profile beyond the geometric focus of the lens, which evolves into a ring shape closer to the focusing lens. These preliminary results suggest that shorter wavelengths may be beneficial for longer scale, ms-duration guiding of optical signals.

 

P2.10: Understanding chromatic aberrations in 4f few-cycle pulse shapers

D. A. Heberle, Cornell University (United States); C. T. Middleton, PhaseTech Spectroscopy, Inc. (United States); N. R. Flemens, J. A. Moses, Cornell University (United States)

Abstract
We find strong ties between the pulse shaper 4f geometry and the optical aberrations that limit 4f pulse shaper performance when used with bandwidth corresponding to a few-cycle pulse. By investigating aberrations imparted on half-octave optical pulses in two experimentally realized and commonly used Fourier-plane pulse-shaping devices, (1) a cylindrical-mirror design and (2) a 1-D off-axis parabolic-mirror design, we find key differences in spatial chirp, chromatic astigmatism, and integrity of the Fourier plane. A ray-tracing analysis supports experimental measurements. On one hand, the cylindrical-mirror design minimizes chromatic astigmatism and maintains the focus quality of the input beam but induces spatial chirp. On the other, the 1-D off-axis parabolic-mirror design minimizes the spatial chirp but induces severe chromatic astigmatism. An understanding of this tradeoff is essential for the development of few- and single-cycle frequency-domain technologies relying on 4f pulse shaping.

 

P2.11: Temporal characterization of laser pulses through tunneling ionization from low-ionization-potential gases

W. Cho,Gwangju Institute of Science and Technology (Korea, Republic of); K. Kim, S. Hwang, Institute for Basic Science (Korea, Republic of)

Abstract
We demonstrate the temporal characterization of laser pulses using a method called the tunneling ionization with a perturbation for the time-domain observation of an electric field (TIPTOE). The TIPTOE method can be generally applied for a broad wavelength range from UV to IR. Since it utilizes extreme nonlinearity of ionization, it requires a certain amount of pulse energy to induce ionization. In this work, we estimate the required pulse energy for various gaseous targets. We calculate the total ionization yield by solving time dependent Schrodinger equation for Ar, O2, Xe, and difluoroethane. It is found that the required pulse energy for the TIPTOE measurement can be greatly reduced by using low-ionization-potential gases. Therefore, the use of the low ionization potential gas will extend the applicability of the TIPTOE methods even for low power laser systems.

 

P2.12: Compact in-line interferometry for the temporal measurement of polarized ultrashort laser pulses

B. Alonso, University of Salamanca (Spain) and Sphere Ultrafast Photonics (Portugal); Í. J. Sola, University of Salamanca (Spain)

Abstract
We use a suitable thickness birefringent plate (3 mm calcite) to introduce a relative delay between two orthogonal projections of an arbitrarily polarized ultrashort laser pulse. After the birefringent plate, a linear polarizer is used to select both spectral projections. Additionally, we select an intermediate projection to produce and measure their spectral interferences, which encode their relative phase. The system is calibrated in amplitude and phase, while the measurement is completed with a temporal measurement of one of the projections. We show the validity by measuring different polarization gates.

 

P2.13: All-standard components highly-sensitive SHG-FROG for characterization of weak picosecond pulses at 1030 nm

P. Susnjar, Faculty of Mechanical Engineering, University of Ljubljana (Slovenia); T. Jones, R. Trebino, School of Physics, Georgia Institute of Technology (United States); R. Petkovsek, Faculty of Mechanical Engineering, University of Ljubljana (Slovenia)

Abstract
We present a SHG-FROG experimental setup optimized for characterization of weak picosecond pulses with a central wavelength of 1030 nm. A collinear geometry and a tight focusing in a 1-mm thick PPLN crystal are applied for optimal nonlinear conversion. All frequency-doubled light is collected by a spectrometer using a focal spot in a crystal as its entrance slit with a spectral resolution below 30 pm. This combined, we demonstrate measurement sensitivity of 2.0×10^-3 mW^2 (defined as the minimum product of the peak and average pulse powers at which a reliable nonlinear signal can be detected).

 

P2.14: Sampling limited high-definition acousto-optic femtosecond pulse shaping

K. B. Yushkov, V. Molchanov, National Univ of Science and Technology “MISIS” (Russian Federation)

Abstract
Arbitrary shaping of ultrashort laser pulse is of great importance in numerous applications. Accuracy of pulses shaping strongly depends on the algorithms used to create a dispersive structure modifying the transmitted optical spectrum. We analyze and compare different strategies for generating acousto-optic chirped Bragg gratings using fundamentals of information theory. In particular, dispersive method of synthesis ultrasonic waveforms for programmable acousto-optic filters based on discrete Fourier transform is studied. Based on general properties of discrete functions we prove that the maximum of the induced group delay dispersion is limited by the sampling theorem and equals to a half of the value corresponding to the Bragg grating aperture. The results are 6 dB improvement in contrast in binary spectral shaping mode and reduction of phase-and-amplitude couplings in phase only pulse replication mode.

 

P2.15: Broadband few-cycle pulse characterization by third-harmonic dispersion-scan in multilayer and optically improved functionalized graphene coatings

T. S. Gomes, M. Canhota, H. Crespo, Faculdade de Ciências da Universidade do Porto (Portugal); M. Miranda, Sphere – Ultrafast Photonics (Portugal); C. Freire, B. Jarrais, REQUIMTE/LAQV (Portugal); B. Kulyk, F. Costa, A. Fernandes, A. Carvalho, I3N (Portugal)

Abstract
We present recent results on third harmonic generation in graphene films with different synthesis conditions. By measuring the non-linear signal as a function of the dispersion applied to the ultrashort pulse, we can fully reconstruct the temporal profile of ultrashort pulses from a Ti:Sa 80 MHz repetition rate oscillator.

 

P2.16: High repetition rate measurement of cross-correlation spectra

D. J. Kane, A. B. Vakhtin, Mesa Photonics LLC (United States)

Abstract
The timing between two ultrafast events can often be measured using cross-correlation techniques. In this work, the optical probe is linearly chirped in an optical fiber, and the relative timing is measured by monitoring a change in the spectrum of the optical probe. Thus, the wavelength of the index change maps directly to the time difference between the pump event (or pulse) and the optical pulse. Spectrometer response times are too slow to measure individual modulated pulses at repetition rates greater than about 100 kHz. We measure the spectrum using fiber dispersion to map wavelength to time. High-speed digitization of the optical waveform records the spectrum. Spectral measurements can be made at very high speeds even up to the repetition rates of modelocked lasers. Using these spectral measurements, we are able to precisely locate spectral features corresponding to expected timing signals. The technique can be made self-calibrating and immune to optical system variations. The probe pulse chirp and probe bandwidth are parameters that can be adjusted to improve timing measurements.

 

P2.17: Dispersion scan technique addressing NIR systems and longer pulse durations of ultrafast fiber lasers systems

R. M. Romero, P. Guerreiro, M. Miranda, Sphere Ultrafast Photonics (Portugal); H. Crespo, Sphere Ultrafast Photonics (Portugal) and IFIMUP-IN and Departamento de Física e Astronomia, Universidade do Porto (Portugal); S. Torres-Peiró, H. Muñoz-Marco, P. Pérez-Millán, FYLA LASER SL (Spain)

Abstract
The dispersion scan (d-scan) technique enables simultaneous compression and measurement of ultrashort laser pulses and has been widely used with both direct and post-compressed pulses from Ti:Sapphire laser systems at 800 nm, with durations ranging from tens of fs to single-cycle 2.2 fs pulses. Few-cycle optical parametric chirped-pulse amplifiers (OPCPAs) and broadband fiber lasers are also being developed at 1 μm to fill the gap for very short pulse sources in this wavelength range. Longer pulse femtosecond fiber lasers operating in the near-infrared (NIR) spectral region and with typical pulse durations in the 100 fs range are an increasingly important technology in many ultrafast applications, such as photonic generation of terahertz radiation or 3D imaging of depleted sensors through the transient current technique based on two photon absorption (TPA-eTCT). In this work, we develop and demonstrate d-scan systems for the measurement and compression of mode-locked fiber lasers at 1 μm and 1.5 μm, with compressed pulse durations ranging from 15 to 150 fs, further confirming the versatility of the d-scan technique in terms of wavelength and pulse duration ranges and its applicability to this important class of femtosecond laser sources.

 

P2.18: Two-cycle pulses in the mid-IR based on hybrid thin plate compression at high average power

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

Abstract
Spectral broadening of initially 50 fs pulses emitted by an OPCPA system around 3.2 μm is experimentally demonstrated through nonlinear propagation in Si and YAG thin crystals at 11 W average power. Crystal temperature measurements revealed thermal limitations due to multi-photon absorption mainly in Si, which are further investigated by numerical modelling. Nevertheless, the Strehl ratio of the output pulses is measured to be as high as 0.9. The sub-100 mrad CEP stability of the OPCPA system is also fully preserved. Complete temporal reconstruction of the compressed pulses is achieved by using a home-built SHFROG device.

 

P2.19: Few-cycle mid-IR pulses by DFG in BaGa2GeSe6

L. Maidment, U. Elu, L. Vamos, T. Steinle, F. Haberstroh, ICFO – The Institute of Photonic Sciences (Spain); V. Badikov, D. Badikov, High Technologies Laboratory, Kuban State University (Russian Federation); V. Petrov, Max-Born-Institute for Nonlinear Optics and Ultrafast Spectroscopy (Germany); J. Biegert, ICFO – The Institute of Photonic Sciences (Spain) and ICREA (Spain)

Abstract
Few-cycle pulses at 7 μm with passive carrier-to-envelope phase stability are generated using the newly developed nonlinear material BaGa2GeSe6. The intrinsic phase stability allows us to measure the electric field of the pulses using electro-optic sampling, giving a pulse duration of 91 fs (< 4 optical cycles). Up to 21 pJ pulse energy (2.1 mW at 100 MHz) is generated with spectral extent from 5.9 to 8.3 μm in collinear geometry. This represents an efficiency 4 times greater than with GaSe.

 

P2.20: Waveform stability of intrapulse difference-frequency generation characterized via electro-optic sampling

S. Hussain, C. Hofer, Max Planck Institute of Quantum Optics (MPQ) (Germany) and Ludwig-Maximilians- Universität München (Germany); W. Schweinberger, Ludwig-Maximilians-Universität München (Germany) and King Saud University (Saudi Arabia); T. Buberl, Max Planck Institute of Quantum Optics (MPQ) (Germany); M. Huber, Ludwig-Maximilians-Universität München (Germany); N. Karpowicz, Max Planck Institute of Quantum Optics (MPQ) (Germany); F. Krausz, Max Planck Institute of Quantum Optics (MPQ) (Germany) and Ludwig-Maximilians-Universität München (Germany); I. Pupeza, Max Planck Institute of Quantum Optics (MPQ) (Germany)

Abstract
Controlling the electric field of trains of ultrashort laser pulses lies at the core of time-resolved measurements of the (consequences of) light-induced polarization in matter, as well as of precision measurements of quantum transitions. Intrapulse difference-frequency generation (IPDFG) affords such control intrinsically, producing waveform-stable pulses. Here, we employ electro-optic sampling as a broadband (both in the radio-frequency and in the optical domain), highly sensitive metrology for the stability of optical waveforms. In the 1-Hz-to-0.63-MHz band, we measure field amplitude fluctuations on the order of 0.2%, and temporal jitter between the center of mass of 16-fs near-infrared pulses spectrally centered at 1μm and driving IPDFG, and the emerging, nearly-octave-spanning mid-infrared field spectrally centered at 8.6 μm, of less than 4 as, corresponding to less than 1 mrad phase jitter. These results both confirm the outstanding phase stability of IPDFG, and provide a sensitivity high enough to investigate subtle effects of oscillator excess noise on the stability of waveforms generated via IPDFG.

 

P2.21: Toward Watt-level optical parametric amplification in the molecular fingerprint region driven by a high repetition rate thulium-doped fiber laser

T. Heuermann, Friedrich-Schiller University Jena (Germany) and Helmholtz-Institute Jena (Germany); M. Gebhardt, Z. Wang, Friedrich-Schiller University Jena (Germany); C. Gaida, Active Fiber Systems GmbH (Germany); F. Maes, University of Laval (Canada); C. Jáuregui Misas, Friedrich-Schiller University Jena (Germany); J. Limpert, Friedrich-Schiller University Jena (Germany) and Helmholtz-Institute Jena (Germany) and Fraunhofer Institute for Applied Optics and Precision Engineering (Germany)

Abstract
Tm-doped fiber lasers operating at 2 μm wavelength have a huge potential to serve as a power scalable pump source for the conversion of radiation into wavelength regions hardly accessible by mature 1μm drivers. Converting the radiation towards the mid infrared region is interesting for applications in today’s life sciences as many important molecules feature numerous absorption lines in this so called mid infrared fingerprint region. Only non-oxide crystals offer a transmission band beyond 5 μm, but at the cost of a small bandgap. This renders them unsuitable for short wavelength drivers. Therefore, increasing the driving laser wavelength is inevitable for efficient average power scaling towards this wavelength region. In this contribution we present efficient optical parametric amplification of mid-infrared radiation in the wavelength region beyond 5μm driven by a Tm doped fiber laser at 2μm wavelength. In a first proof of principle demonstration 9 W of pump power at 200 kHz repetition rate and 270 fs of pulse duration were used to pump a 2mm GaSe crystal. Here, 360 mW of mid IR power are generated, corresponding to 4.3% of conversion efficiency with a spectrum spanning from 7.2 μm to 8.2 μm (-10 dB width). In a next step the full laser power will be utilized. Assuming a similar conversion efficiency, 1.6 W of average idler power can be expected. By further optimizing the seed and the bandwidth, multi-watt octave spanning idler beams can be expected from this scheme in the future.

 

P2.22: High Power Broadband THz Generation in Cryogenically Cooled GaP Driven by a sub-100 fs Thin-Disk Laser

F. Meyer,N. Hekmat, T. Vogel, A. Omar, S. Mansourzadeh, F. Fobbe, M. Saraceno, Y. Wang, C. Saraceno, Ruhr University Bochum (Germany)

Abstract
We generate broadband THz radiation by optical rectification in GaP driven by a 115 W modelocked thin-disk oscillator at 13.4 MHz repetition rate. It is shown that compressing the pulse duration to sub-100 fs using a Heriott type multi-pass cell, the conversion efficiency can be significantly increased, resulting in mW level average powers. Additionally, we present data on cryogenic cooling, suggesting, that further power scaling is possible.

 

P2.23: 5-20 µm, mid-infrared pulse generation from a 16 MHz, Yb:YAG thin-disk oscillator in polycrystalline ZnSe

H. Wang, Max-Planck-Institut für Quantenoptik (Germany) and Ludwig-Maximilians-Universität München, Fakultät für Physik (Germany); G. Barbiero, F. Krausz, Max-Planck-Institut für Quantenoptik (Germany) and Ludwig-Maximilians-Universität München (Germany); H. Fattahi, Max-Planck-Institut für Quantenoptik (Germany)

Abstract
We report on multi-octave, mid-infrared pulse generation in birefringent LGS crystal and polycrystalline ZnSe via intrapulse difference frequency generation, driven by 10 fs, 32 W, 16 MHz pulses from a Yb:YAG Kerr-lens mode-locked thin-disk oscillator.

 

P2.24: Broadband mid-infrared pulse generation in GaSe with an Yb:KGW laser-based dual OPA setup

R. Budriūnas, Vilnius University Laser Research Center (Lithuania) and Light Conversion Ltd (Lithuania); A. Varanavičius, Vilnius University Laser Research Center (Lithuania)

Abstract
We present a simple technique for generating broadly tunable, broadband pulses in the mid-infrared. The method is based on mixing ~30fs pulses at 1.8μm with narrowband pulses tuned through 2.5-4.5μm in GaSe crystal. Output pulses with bandwidths of 240-730cm-1, durations down to 31fs, good pulse quality, and nearly-Gaussian spatial modes are produced in the 3- 6μm range with ~10% conversion efficiency from 1.8μm pump pulses to mid-infrared output (at 3-4μm). The scheme could be readily adapted to a wide variety of Yb-doped lasers already present in many research labs.

 

P2.25: Generation of mid-infrared supercontinuum in polarization maintained fluoride fibers using a femtosecond Tm:YAP laser

S. Rezvani, Toyota Technological Institute (Japan); Y. Nomura, Institute for Molecular Science (Japan); K. Ogawa, Fiberlabs Inc. (Japan); T. Fuji, Toyota Technological Institute (Japan) and Institute for Molecular Science (Japan)

Abstract
Mid-infrared (MIR) supercontinuum generation in polarization-maintained (PM) fluoride fibers has been demonstrated. An elliptical core ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber was pumped by 0.5 μJ femtosecond pulses from a home-built 2 μm Tm:YAP (Tm:YAlO3) regenerative amplifier, and a stable supercontinuum spanning up to 4 μm was generated. The intensity and phase of the supercontinuum were obtained using cross-correlation frequency-resolved optical gating (XFROG). The complex structure of the retrieved spectrum from the XFROG result due to the pulse-to-pulse spectrum instability was disappeared by reducing the round trip number of the regenerative amplifier, namely, improving the quality of the incident pulse spectrum. The result is very important for phase sensitive applications of the supercontinuum, in particular, for the seed source of a femtosecond MIR optical parametric amplifier.

 

P2.26: Time-domain, field-resolving spectrometer for mid-infrared molecular spectroscopy

S. Hussain, Max Planck Institute of Quantum Optics (MPQ) (Germany) and Ludwig-Maximilians-Universität München (LMU) (Germany); W. Schweinberger, Ludwig-Maximilians-Universität München (LMU) (Germany) and King Saud University (Saudi Arabia); M. Huber, Ludwig-Maximilians-Universität München (LMU) (Germany); C. Hofer, Max Planck Institute of Quantum Optics (MPQ) (Germany) and Ludwig-Maximilians-Universität München (LMU) (Germany); M. Trubetskov, D. Gerz, Max Planck Institute of Quantum Optics (MPQ) (Germany); K. Fritsch, M. Poetzlberger, L. Vamos, T. Amotchkina, V. Pervak, O. Pronin, Ludwig- Maximilians-Universität München (LMU) (Germany); F. Krausz, Max Planck Institute of Quantum Optics (MPQ) (Germany) and Ludwig-Maximilians-Universität München (LMU) (Germany); I. Pupeza, Max Planck Institute of Quantum Optics (MPQ) (Germany)

Abstract
We present an apparatus for sensitive and high-dynamic-range, time-domain, electric-field-resolved measurements of long-wave mid-infrared waveforms. A state-of-the-art Yb-modelocked-oscillator based femtosecond frontend provides a 28-MHzrepetition- rate train of 16-fs, 1-μm pulses with an average power of 60 W. These generate waveform-stable few-cycle mid-infrared transients via intrapulse difference-frequency mixing in a nonlinear crystal, and are also used for sub-optical-cycle temporal gating in electro-optic sampling. We report thermal-background-free, linear field detection of 13 orders of magnitude in intensity around a central wavelength of 8.6 μm, capable of measuring pulses with the lowest signal detectable amounting to 0.0001 photons per pulse. The sensitivity and high dynamic range of detection, the confinement of the infrared light to sub-two-cycle pulses with an intensity full width at half maximum of 56 fs, and the robustness against thermal background, render this system ideal for infrared vibrational spectroscopy of strongly absorbing samples, such as biofluids, live cells and biological tissue.

 

P2.27: Generation of broadband THz beams with azimuthally modulated phase and intensity by femtosecond laser pulses in air plasma

V. Vaicaitis, M. Ivanov, Vilnius University (Lithuania); I. Thiele, Chalmers University of Technology (Sweden); D. Buozius, I. Juchneviciute, Vilnius University (Lithuania); S. Skupin, Université Lyon (France); L. Bergé, CEA, DAM, DIF (France)

Abstract
We report efficient generation of the broadband terahertz (THz) radiation by bichromatic femtosecond laser pulses with flat phase fronts or with a phase singularity focused in air. As a pump source, the fundamental and second harmonic radiations of a femtosecond Ti:sapphire laser were used. While the fundamental laser beam had Gaussian intensity distribution and a flat phase front, the second harmonic beam had either flat or helical phase front forming an optical vortex. In both cases the angular spectra ofTHz radiation and azimuthal phase distributions of THz beams were investigated. It was found that when both the fundamental and second harmonic laser pulses had Gaussian profiles, the resulting THz radiation was generated as an axially symmetric cone with a flat phase front. However, when the Gaussian second harmonic beam was replaced by the one with optical singularity, the intensity and the phase of generated THz cone became modulated along the azimuthal angle. The spectrum of generated THz pulses spanned up to 50 THz in both cases. Our theoretical analysis based on the photocurrent model was in good agreement with the experimental data.

 

P2.28: New photocathode laser for X-ray free electron Laser in DESY with flexible pulse shape

C. Li, I. Hartl, L. Winkelmann, A. Choudhuri, DESY (Germany); M. Frede, O. Puncken, neoLASE GmbH (Germany)

Abstract
Novel operational regimes of X-ray Free-Electron Lasers (XFELs) require advanced laser systems offering a high degree of flexibility of their output pulse parameters. In our case, the photocathode laser, which generates electrons from a RF photocathode gun, defines the efficiency and flexibility of the XFEL. Thus full control of the spatial (flat-top or truncated Gaussian) and temporal shape (Gaussian or temporal flat-top: 1 ps – 20 ps) of the deep UV laser pulses is a powerful tool to tailor the charge, size and length of the generated electron bunches for optimal emittance. In this submission a burst-mode photocathode laser for the soft- X-ray FLASH XFEL and the hard-X-ray European XFEL in Hamburg, Germany is presented, which can deliver pulses with flexible duration from 1 ps to 20 ps and single pulse energies up to 200 μJ in NIR (expected > 20μJ DUV) at an pulse repetition rate of up-to 1 MHz in up to 1 ms long bursts at 10 Hz burst-repetition rate.

 

P2.29: The role of laser shaping in microbunching instability suppression and seeded X-ray free electron emission

R. Lemons, Colorado School of Mines (United States); J. Tang, W. Liu, S. Vetter, T. Maxwell, F. Decker, A. Lutman, J. Krzywinski, G. Marcus, S. Moeller, D. Ratner, Z. Huang, S. Carbajo, SLAC National Accelerator Laboratory (United States)

Abstract
We present theoretical and experimental results on the use transversely-shaped laser modes at LCLS resulting in better suppression of the e-beam microbunching instability and its impact on self-seeded X-ray FEL performance.

 

P2.30: A femtosecond timing scheme for XUV-FELs based on conversion to THz frequencies

I. Ilyakov, Helmholtz-Zentrum Dresden-Rossendorf (Germany); N. Agarwal, R. Carley, European XFEL GmbH (Germany); J.-C. Deinert, Helmholtz-Zentrum Dresden-Rossendorf (Germany); A. Yaroslavtsev, J. Liu, L. Le Guyader, European XFEL GmbH (Germany); L. Foglia, R. Mincigrucci, E. Principi, G. Kurdi, Elettra-Sincrotrone Trieste (Italy); T. Kampfrath, Freie Universität Berlin/Fritz Haber Institute of the Max Planck Society (Germany); S. Kovalev, Helmholtz-Zentrum Dresden-Rossendorf (Germany); M. Gensch, Technische Universität Berlin/German Aerospace Center (Germany); A. Scherz, European XFEL GmbH (Germany).

Abstract
A new approach for timing between a femtosecond XUV-FEL and an external NIR femtosecond laser is experimentally demonstrated. The technique is based on optical rectification of the XUV pulses in a spintronic multilayer. The arrival time of the resulting THz pulse is measured with an established electro-optic single-shot technique. Using the proposed scheme, timing between the FEL and external laser system of better than 20 fs was achieved. The demonstrated approach is robust, can be operated utilizing the low-energy spent XUV pulses behind the actual experiments and up to high repetition rates in the few 100 kHz range. It thereby overcomes the drawbacks of other proposed or established timing schemes.

 

P2.31: Calibration of CEP dependent electron spectra

D. Hoff, Friedrich-Schiller-Univ Jena (Germany)

Abstract
Here we present a technique to determine the absolute carrier-envelope phase (CEP) dependence of electron rescattering in strong-field ionization. First, this requires a detailed knowledge of the spatial dependence of the CEP in the focus of few-cycle laser pulses. Second, one needs a well known reference to calibrate the process to the CEP. In our case we use ab-initio 3D-TDSE simulations of above-threshold ionization (ATI) of atomic Hydrogen to calibrate experimental electron spectra of H, these can then be used to calibrate ATI-spectra of Xenon. The latter can serve as a reference for the electron rescattering at noble gases and nanostructures. With this calibration it is possible to unravel different contributions that are responsible for a phase shift between atomic gases and nanostructures.

 

P2.32: A high resolution XUV grating monochromator for the spectral selection of high order harmonics

N. Fabris, P. Miotti, F. Frassetto, L. Poletto, CNR-IFN Padova (Italy)

Abstract
A new monochromator with high spectral resolution in the extreme ultraviolet (XUV) has been developed for high-order laser harmonics selection. The system has three optical elements: a cylindrical (or spherical) focusing mirror, a uniform-line-spaced plane grating and a plane mirror. The last element is required to maintain the focus on a fixed slit when the grating subtended angle is changed in order to minimize the spectral defocusing aberration. The parameters of the focusing mirror are determined to introduce a coma that compensates for the coma given by the grating. The possibility of using two interchangeable gratings made the set-up optimized for a broad energy range of 12-50 eV. As a design test case, the set-up has been applied to the selection of the discrete spectral lines emitted by a gasdischarge lamp as XUV source obtaining a below-10-meV bandwidth.

 

P2.33: A compact, sub-100-fs RF gun for ultrafast electron diffraction

K. Ito, E. Haraguchi, K. Kaneshima, T. Sekikawa, Hokkaido University (Japan)

Abstract
To develop a circularly polarized (CP) extreme ultraviolet light source, the ellipticities of CP high harmonics at 47 and 50 nm monochromatized by a time-delay compensated monochromator (TDCM) were characterized using a reflection polarizer. The ellipticity of the harmonic at 47 nm selected by the TDCM was 0.29. The reflectance and phase shift of the high harmonic upon diffraction on the toroidal gratings constituting the TDCM were also evaluated. The partial compensation of the polarization distortion by the TDCM was implemented by manipulating the polarization of the driving laser field and by generating an elliptically polarized high harmonic. The ellipticity was compensated by the anisotropy of the diffraction coefficients and improved to 0.84. This single-order CP light source can be used to investigate electromagnetic and chiral phenomena.

 

P2.34: Central Laser Facility Artemis Upgrade: New Capabilities for X-Ray Spectroscopy

R. T. Chapman, G. M. Greetham, G. Karras, C. E. Sanders, A. S. Wyatt, Y. Zhang, M. Towrie, E. Springate, Science and Technology Facilities Council (United Kingdom)

Abstract
The ULTRA and Artemis laboratories provide ultrafast dynamics and spectroscopy facilities for UK and international scientists, addressing problems across physics, chemistry and biology. Synergies in the technology and experimental approaches of these two facilities will be exploited in the coming years by relocation of Artemis to the Research Complex at Harwell, the home of ULTRA. The acquisition of a new 100 kHz optical parametric chirped pulse amplifier laser system will upgrade the facilities and underpin future laser technology for both. Additionally, the introduction of a third amplifier to the existing Artemis Ti:sapphire laser to boost the energy to 2x 10 mJ will be used to generate higher energy pulses in the ultraviolet and short-wave infrared spectral regions to enhance coherent diffraction imaging and atomic and molecular optics experimental capabilities. We present an overview of the new laboratory and laser system to be installed in 2019.

 

P2.35: Two-color HHG in the regime of high-frequency atomic stabilization

M. Emelin, M. Ryabikin, Institute of Applied Physics, RAS (Russian Federation) and Prokhorov General Physics Institute, RAS (Russian Federation)

Abstract
Two-color high-harmonic generation (HHG) in the regime of high-frequency atomic stabilization is studied on the basis of ab initio numerical calculations. Generation of photons with less that 1 angstrom wavelength is demonstrated. It is shown also that two-color field with optimal parameters found allows to increase the efficiency of the hardest photons production significantly.

 

P2.36: Wavelength scaling laws for high-order harmonic generation with mid- and long-wave infrared laser pulses

A. Emelina, M. Emelin, Institute of Applied Physics, RAS (Russian Federation) and Prokhorov General Physics Institute, RAS (Russian Federation); M. Ryabikin, Institute of Applied Physics,RAS (Russian Federation) and Prokhorov General Physics Institute, RAS (Russian Federation)

Abstract
Significant progress has been recently achieved in the development of high-power femtosecond laser sources whose wavelengths range from 1.5 to 4 μm and beyond. This has opened up new perspectives in the research of strong-field laser-matter interactions. Due to a favorable wavelength scaling of the electron ponderomotive energy, higher-energy photons can be generated via high-order harmonic generation (HHG) using longer-wavelength drivers. On the other hand, as shown in the recent studies, there are a number of effects whose importance for HHG increases with increasing laser wavelength. These effects generally result in decreasing the harmonic yield and changing the shape of the emission spectrum. Hence, the detailed study of the dependence of HHG yield on the laser wavelength has become important issue for producing intense extremely short XUV and x-ray pulses using HHG driven by mid- and long-wave infrared lasers. Here, we address this issue by calculating the HHG spectra for laser wavelengths ranging from 2 to 20 μm. Using strong-field approximation (SFA) modified to take into account the atomic bound-state depletion and the effect of the magnetic field of a laser pulse, we study the dynamics of the field-ionized electron and the photon emission produced due to its recollisions with the parent ion. We show that different regions of the HHG spectrum behave differently with the laser wavelength and discuss the origins of this behavior. We derive analytical formulas that give the wavelength scaling laws for harmonic yield in different regions of the HHG spectra in good agreement with the SFA calculations.

 

P2.37: Time-resolved Optical Pump-THz Ellipsometer Probe Measurements with Wave-front Tilt Scheme

B. Kang, G. Gäumann, T. Feurer, University of Bern (Switzerland)

Abstract
We demonstrate a NIR-pump/THz-ellipsometer probe spectrometer together with proof of principle measurements on UHR-Si. To overcome the velocity mismatch between NIR pump and THz probe at large ellipsometer angles we introduce the pulsefront tilt scheme for the pump. The measured time-resolved dielectric properties of NIR-pumped Si are in good agreement with 2 temperature model simulation.

 

P2.38: Ultrafast single-cycle far-infrared pulses for imaging pump-probe dynamics on the atomic scale

V. Jelic, Michigan State University (United States) and University of Alberta (Canada); Y. Luo, P. H. Nguyen, J. A. Calzada, D. Mildenberger, Y. Liu, F. A. Hegmann, University of Alberta (Canada)

Abstract
Recent progress in THz-pulse-coupled scanning tunneling microscopy (THz-STM) has demonstrated that ultrafast single-cycle far-infrared transients can non-resonantly control electron tunneling at sub-nanometer length scales and sub-picosecond timescales [1–7]. The THz pulse electric field couples to the atomically sharp tip of the STM, generating a spatially and temporally localized ultrafast tunnel current that can be used to explore the dynamics of atoms [4,6] and molecules [2] on surfaces. In the work presented here, hundreds of electrons are rectified across the tunnel junction per THz pulse, while imaging a photoexcited GaAs(110) surface with a spatial resolution of 3 Å and a temporal resolution of 500 fs. The STM topography image and ultrafast THz-STM image are acquired simultaneously as the tip is raster scanned across the sample surface.

 

P2.39: Red-shifted conical emission from high-power ultrafast optical vortices

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

Abstract
Structured laser beams carrying orbital angular momentum (OAM) represent a promising tool in applications such as optical communication, microscopy, particle manipulation, and astrophysics. At high powers the OAM beams propagate in the nonlinear regime and produce self-guiding structures which differ from those formed by a regular Gaussian beam. We demonstrate experimentally that the conical emission of OAM vortex beams shifts dominantly towards longer wavelengths.

 

P2.40: Femtosecond to microsecond photophysical studies of a novel free base phthalocyanine

S. Bhattacharya Jr., ACRHEM, University of Hyderabad (India) and ACRHEM, University of Hyderabad (India); S. Paul Sr., School of Chemistry, University of Hyderabad (India); S. S. Hossain Sr., School of Chemistry (India); S. K. Raavi, Indian Institute of Technology Hyderabad (India); G. Lingamallu, CSIR-Indian Institute of Chemical Technology (India); S. V. Rao, ACRHEM (India); A. Samanta, School of Chemistry (India)

Abstract
A novel free base phthalocyanine, ImHPc (C140H116N16) was developed by incorporating the triphenyl imidazole moiety at its peripheral positions. A detailed analysis of the UV-visible absorption, emission and transient absorption spectra were studied. The Emission studies reveal the fluorescence peak 695 nm to 705 nm and the time-resolved fluorescence data exposed radiative lifetimes of typically few ns. Transient absorption studies (TAS) reveal two singlet lifetimes in picoseconds while single triplet lifetime in microseconds. This makes our molecule ideal for applications in photonics like solar cells and photomedicine like fluorescence imagine, Photodynamic therapy (PDT), etc.

 

P2.41: A compact, sub-100-fs RF gun for ultrafast electron diffraction

M. Fakhari, University of Hamburg (Germany); K. Floetmann, DESY (Germany); D. Miller, Max Planck Institute for the Structure and Dynamics of Matter (Germany); W. Hillert, F. Kärtner, University of Hamburg (Germany)

Abstract
A compact half-cell RF gun for ultrafast electron diffraction is presented. The designed and fabricated gun requires only 10 kW input power to accelerate a 1 pC electron bunch up to 200 keV with a spot size of 100 um and 30 fs duration.

 

P2.42: Spectrum and waveform of secondary radiation generated during ionization of multielectron atoms by ultrashort laser pulses

A. A. SilaevA. A. Romanov, N. V. Vvedenskii, Institute of Applied Physics RAS (Russian Federation) and Lobachevsky State University of Nizhny Novgorod (Russian Federation); M. V. Frolov, Voronezh State University (Russian Federation)

Abstract
We develop the computer code for numerical simulation of the interaction of ultrashort laser pulses with noble-gas atoms based on the solution of the time-dependent Kohn–Sham equations. The nonlinear electron currents excited during the ionization of argon atoms by intense two-color laser pulses are calculated. We show the importance of taking into account multielectron effects in the calculation of spectrum and waveform of secondary radiation generated at high-intense laser pulses.

 

P2.43: Nonlinear light-matter interaction measurements using digital holography

B. Momgaudis, L. Smalakys, M. Vengris, A. Melninkaitis, Vilnius Univ (Lithuania)

Abstract
A better understanding of interaction between light and matter during optical damage formation, especially when taking into account optical damage fatigue, requires sensitive quantitative evaluation of various parameters. One of them, the absorbed energy density is considered as the most universal criterion to define the optical damage. In this work, a recently developed method suitable for quantitative assessment of nonlinearly absorbed energy based on time resolved digital holography is presented. During single pulse interaction with transparent media energy is deposited into material due to nonlinear absorption. This results in dynamic temperature driven refractive index change. The well-established method of digital holography can be used to record this time dependent spatial distribution of refractive index change. Numerical methods then can be used to relate the experimental data to total absorbed energy. As a proof of concept, absorbed energy in fused silica sample is investigated while changing various parameters like: time delay, pulse energy and accumulation of pulses. It is shown that the method is capable of accurate evaluation of absorbed energy in a limited time delay window, that material modification begins when the sample absorbed more than 10% of incident energy, while more than 15% results in catastrophic damage.

 

P2.44: Ultrafast Transient Absorption of Adamantyl-Phenol

M. Forjan, Institute of Physics (Croatia)

Abstract
Ultrafast dynamics of adamantyl-phenol was studied by measuring time-resolved absorption changes using transient absorption spectroscopy technique. Adamantyl-phenol molecules dissolved in acetonitrile-water mixture (1:1) were excited by femtosecond laser pulses with the wavelength of 267nm (pump pulse) while their absorption as a function of time was tested with the probe pulses. Probe pulse spectrum was supercontinuum generated in calcium-fluoride (CaF2) crystal pumped by 800nm. Resulting signal was positive, meaning the molecules have negligible fluorescence. After the excitation to first excited electronic state photochemical reaction of photodehydratation takes place and the formation of quinone methide (QM) begins via conical intersection. Quinone methides are important intermediates in the chemistry and photochemistry of phenols, and they became interesting over the past two decades owing to their biological activity and increasing number of applications in organic synthesis. Quantum-chemical TDDFT calculations indicate immediate ground state QM formation and the simulated ground state QM spectra is compared to measured one. Obtained results proved the functionality of the used experimental setup which will be used for future research and ultrafast transient absorption measurements of many different samples.