Laser induced x-ray fluorescence were observed against laser polarization ellipticity. While emission from krypton peaks at linear polarization, a signature of recollision, emission from neon shows opposite trend. We attribute it to two competing processes.

More and more ultrafast few-cycle laser systems for strong field physics are operating at ultrahigh repetition rates reaching 50 kHz and more, where the extraction of the carrier-envelope phase (CEP) for each single pulse at higher repetition rates remains a challenge. We report here on a technique allowing the measurement of the CEP up to tens of MHz and it is demonstrated here at 100 kHz. Real time single-shot measurement/tagging of CEP at full (100 kHz) repetition rate is achieved by combining dispersive Fourier transform (DFT, TOUCAN) with field-programmable gate array (FPGA) technology for on-the-fly phase extraction from an 2f-to-f signal mapped to time domain.

A Gyulakenyér Kft ellátási láncáról, történetéről, működéséről írunk. A nagy hagyományokkal rendelkező cég Gyula város és vonzáskörzete pékségellátásának központi funkcióját tölti be. Ismertetjük a cég ellátási láncát a megrendeléstől, a beszerzésen át a gyártáson és a csomagoláson át a szállításig és az értékesítésig. Az esettanulmány végén ismertetjük saját elképzeléseinket a logisztikai fejlesztés területén.

Above-threshold ionization spectra from cesium are measured as a function of the carrier-envelope phase (CEP) using laser pulses centered at 3.1  μm wavelength. The directional asymmetry in the energy spectra of backscattered electrons oscillates three times, rather than once, as the CEP is changed from 0 to 2π. Using the improved strong-field approximation, we show that the unusual behavior arises from the interference of few quantum orbits. We discuss the conditions for observing the high-order CEP dependence, and draw an analogy with time-domain holography with electron wave packets.

One of the most widespread and reliable techniques for spectral phase characterization of optical elements is spectrally resolved interferometry (SRI) [1] , [2] , which utilizes a two-arm interferometer illuminated by a broadband light source and a spectrometer to record the generated spectral fringes. The investigated optical element is placed in one arm, and its spectral phase can be extracted by using Fourier-transform (FT) based methods [3] , [4] for instance, which are the most accurate, even when low dispersion values are to be determined. One detriment to this evaluation method, that it requires high spectral resolution. Considering that most of the spectrometers in the mid-infrared (MIR) region have typically a few nm spectral resolution, we propose two alternative methods for measurements in this spectral region.

This paper presents a second harmonic assisted spectrally resolved interferometric technique that can overcome the limited spectral resolution of commercially available spectrometers in the mid-infrared. The discussed scheme was validated by measuring the group delay of several well-known and frequently used materials. Our main motivation was to characterize the spectral phase shift of newly designed and manufactured dispersive mirrors to be used for mid-infrared (MIR) post-compression. These mirrors were successfully implemented in the post-compression stage of our MIR laser system, where pulse duration was shortened below two optical cycles and the pulse peak power increased by 30.3% compared to the original output.

We present single-shot electron velocity-map images of nanoplasmas generated from doped helium nanodroplets and neon clusters by intense near-infrared and mid-infrared laser pulses. We report a large variety of signal types, most crucially depending on the cluster size. The common feature is a two-component distribution for each single-cluster event: a bright inner part with nearly circular shape corresponding to electron energies up to a few eV, surrounded by an extended background of more energetic electrons. The total counts and energy of the electrons in the inner part are strongly correlated and follow a simple power-law dependence. Deviations from the circular shape of the inner electrons observed for neon clusters and large helium nanodroplets indicate non-spherical shapes of the neutral clusters. The dependence of the measured electron energies on the extraction voltage of the spectrometer indicates that the evolution of the nanoplasma is significantly affected by the presence of an external electric field. This conjecture is confirmed by molecular dynamics simulations, which reproduce the salient features of the experimental electron spectra.

The interpretation of experimental data from novel mid-infrared few-cycle laser sources requires an understanding of ionization mechanisms and knowledge about related ion yields. Experimental studies have indicated sequential double ionization as the dominant process above 1014 W cm−2. These results contradict a recent prediction that in this spectral region, non-sequential processes dominate the double ionization of xenon up to intensities of about 1015 W cm−2. In either case, the ratio of doubly to singly charged xenon yield reported in previous studies has been limited to a few percent, indicating a regime well below the onset of saturation of the double ionization process. We present an experimental study of double ionization of xenon and krypton atoms exposed to intense near four-cycle pulses at 3.2 μm. Our experiments rely on the ion microscopy technique, which facilitates the detection of ions originating from a restricted region within the interaction volume, thereby reducing the impact of focal averaging. Our measurements suggest that at intensities of close to 1.2 × 1014 W cm−2, double ionization of xenon and krypton is already significantly saturated. In particular, we find a doubly to singly charged yield ratio of about 75 percent for xenon and 25 percent for krypton. We compare our results with the predictions of different models accounting for the effects of volume averaging and focal geometry. We find that in the deeply saturated regime of our experiment, the Perelomov–Popov–Terentyev theory significantly underestimates the observed double ionization yield.

The precise knowledge of spectral phase shift in various optical elements is crucial for applications with ultrashort pulses. Spectrally resolved interferometry is a versatile, commonly used technique to measure material dispersion. However, the bandwidth of the employed light source limits the spectral region where the phase shift can be determined using this method. In this paper, we introduce a modified version of spectrally resolved interferometry, which enables the reconstruction of the spectral phase shift at the fundamental and the second harmonic wavelengths of the illuminating light source from a single interferogram, and hence doubles the evaluation bandwidth originally available. The presented method is experimentally validated by measuring several dielectric and semiconductor material plates.

A simple and cheap technique for post-compression of mid-IR laser pulses relies on nonlinear spectral broadening via SPM in mm-thick optical windows (plates) followed by recompression. Efficient broadening requires peak intensities of ~hundred GW/cm2, which in case of high average power (>10W) drivers puts serious requirements on the used optical materials’ thermal properties, purity, homogeneity, surface quality and LIDT of coatings. Several materials (YAG, fluorides, KBr, Si, ZnSe, ZnS) were tested with 3.2 µm, 13W (130 µJ, 100 kHz), 48 fs pumping. Measured nonlinear absorption, wavefront distortion, spectral broadening and long-term survival as a function of intensity will be shown.

Spectral broadening of 3.2 µm pulses is experimentally demonstrated at 8.2 W average power output through nonlinear propagation in thin crystal plates. Sub-two-cycle compression was achieved with a bulk compressor and custom-made dispersive mirrors.

Output pulses of a 100 kHz mid-infrared OPCPA system are post-compressed from 4.7 cycles down to 2.3 cycles by using a combination of a dielectric and a semiconductor crystal in a hybrid thin plate setup. Efficient spectral broadening is demonstrated with 11 W average input power. After compression the output power reached 6.8 W with exceptional CEP and energy stability for a several hours. The post-compressed pulses were carefully characterized in both temporal and spatial domains, resulting in 2.3-cycle temporal duration at 3.1 mu m central wavelength with a temporal Strehl ratio of 0.73 and a spatial Strehl ratio of 0.97. Thermal limitations due to multiphoton absorption of semiconductors present at this power level are explored by temperature measurements, which are supported by detailed numerical simulations. Upscaling for higher average powers was also investigated.

High-harmonic generation (HHG) in crystals offers a simple, affordable and easily accessible route to carrier-envelope phase (CEP) measurements, which scales favorably towards longer wavelengths. We present measurements of HHG in ZnO using few-cycle pulses at 3.1µm. Thanks to the broad bandwidth of the driving laser pulses, spectral overlap between adjacent harmonic orders is achieved. The resulting spectral interference pattern provides access to the relative harmonic phase, and hence, the CEP.

The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having "drifted away" from the original parent ion.

Since the discovery of attosecond pulses, experiments became possible in material physics at an attosecond timescale [1] , [2] relying on attosecond XUV sources. An ever-increasing number of these experiments are performed at high repetition rate [2] to reduce the acquisition time and improve the signal-to-noise ratio. These experiments require few-cycle driving pulses with either a stabilized carrier envelope phase (CEP) or a pulse tagging strategy [1] . In both cases, the CEP determination is needed on a single shot basis irrespective of the system repetition rate. To this aim, the TOUCAN (Temporal dispersion based One-shot Ultrafast Carrier envelope phase ANalysis) method was developed [3] , which has the potential for every single-shot CEP drift measurement even at MHz repetition rate and low intensities.

In this theoretical work, the performances of ultrafast, carrier-envelope-phase-stable (CEP), mid-IR optical parametric chirped pulse amplification (OPCPA) systems were compared in two different amplification schemes. In the “idler scheme” the mid-IR pulse (idler) is produced in the first difference frequency generation stage of the OPCPA chain and then amplified in the following stages. In the “signal scheme,” the supercontinuum seed is amplified in the OPCPA chain and the mid-IR pulse is generated in the last amplifier stage. According to our results, the idler has higher energy and better energy stability in the idler scheme, while in the signal scheme the signal has the better characteristics in energy and stability. The CEP noise due to the pump intensity fluctuations was found to be lower in the signal scheme. Additionally, chirp optimization revealed that the peak power of the compressed idler and signal pulses at the output of the system is considerably higher if the chirp of the input signal pulse is positive.

This paper presents a single-shot technique for measuring CEP. The Temporal dispersion based One-shot Ultrafast Carrier envelope phase Analysis method (TOUCAN) is an arbitrary repetition rate single-shot CEP drift measurement technique based on dispersive Fourier transformations and has been experimentally tested at 100 kHz. TOUCAN was validated by a direct comparison of decimated data with an independent traditional CEP drift measurement technique. The impact of a temporal jitter on the CEP drift measurement is investigated and a new mitigation technique is shown to produce high accuracy jitter-free CEP drift extraction.

A 10 kHz KTA-based OPCPA system was numerically investigated with exceptionally short 43 mJ signal and 10 mJ idler output pulses. Thermal limitations of the amplifier were thoroughly analyzed with special care on power stages.

In the past decade ultrafast mid-IR laser sources have experienced fast growing, due to the fact that many applications benefit from long wavelength driving pulses. For instance the cut-off energy for high harmonic generation can be extended to the keV range [1], however the conversion efficiency varies as ~λ -6 [2]. Consequently, the generation of few-tens of mJ mid-IR driving pulses is essential together with high repetition rate in order to compensate the low efficiency in strong field experiments. Commercially available ytterbium-based thin-disk pump lasers are now capable of delivering 200 mJ pulses at 1 kHz repetition rate [3], and it is expected that the average power of these pump lasers will be promoted to the 2 kW range soon. These are ideal sources for pumping mid-IR chirped pulse optical parametric amplifier (OPCPA) systems, thus making it possible to produce multi-mJ pulses in the mid-IR range beyond 1 kHz repetition rate.

We demonstrate an OPCPA driven thin plate compression in the mid-infrared region at 100 kHz with 7 W average output power. The resulting pulses are close to two cycle long and CEP stable.