Search

The performance of regenerative amplifiers at high repetition rates is often limited by the occurrence of bifurcations induced by a destabilization of the pulse-to-pulse dynamics. While bifurcations can be suppressed by increasing the seed energy using dedicated pre-amplifiers, the availability of adjustable filters and control electronics in modern pulse amplifiers allows to exploit feedback strategies to cope with these instabilities. In this paper, we present a theoretical and experimental analysis of active feedback methods to stabilize otherwise unstable operational regimes of regenerative amplifiers. To this end, the dynamics of regenerative amplifiers are investigated starting from a general space-dependent description to obtain a generalization of existing models from the literature. Suitable feedback strategies are then developed utilizing measurements of the output pulse energies or the transmitted pump light, respectively. The effectiveness of the proposed approach is highlighted by experimental results for a Yb:CaF2-based regenerative amplifier.

A conventional hollow core fiber (HCF) scheme is implemented to investigate spectral broadening of Titanium:Sapphire (Ti-Sa) femtosecond laser pulses in saturated hydrocarbon molecules compared to unsaturated ones. While the saturated molecules exhibit a spectral broadening similar to noble gases, for the unsaturated ones with π bonds, broadening towards blue is restrained. Numerical simulations underpin that it is a combination of group velocity dispersion (GVD) and Raman scattering which limits the spectral broadening for the unsaturated molecules. Compression of low energy ∼40fs pulses to ∼8fs using saturated hydrocarbons is demonstrated, suggesting the feasibility of this media for high repetition rate laser pulse compression.

Ultrafast demagnetization, a phenomenon of utmost interest in the context of optical control of magnetically recorded data, has been extensively studied in a variety of different materials. However, only a limited number of studies have investigated the impact of the pump laser wavelength on the process, and only within a narrow spectral range. Performing resonant scattering experiment at the cobalt ${M}_{2,3}$ edges, using extreme ultraviolet radiation photons from a high harmonic source, we studied the ultrafast demagnetization dynamics of Co/Pt multilayers by tuning the pump wavelength to 0.4, 0.8, and 1.8 \ensuremath{\mu}m. We show that the degree of demagnetization at short time scale (100s of fs) is stronger at longer wavelengths. This is explained by the wavelength dependence of both the laser induced heating of the electrons (${T}_{e}\ensuremath{\propto}{\ensuremath{\lambda}}^{2}$) and the spatial distribution of the electromagnetic energy deposited into the multilayer sample.

This works shows a new approach to study the electron recapture process during double and multiple ionization of atoms. This scheme is applicable to non-dissociative processes in molecules, which are not accessible with existing methods based on the measurement of kinetic energy released from fragmentation processes. The experiments show a transition of frustrated double ionization in argon from a non-sequential scenario to a sequential scenario.

We report on unexpected efficient THz generation in organic crystals (DAST and DSTMS) by optical rectification (OR) of intense mid-infrared pulses. The crystals experience superior damage threshold and an ultra-broadband THz spectrum reaching 10 THz.

We investigate the femtosecond supercontinuum generation and compression in layered Kerr media. The condition for extending the setup in a sustainable way is revealed, with characteristic spectral and temporal features. We demonstrate tenfold pulse compression in a single-stage multiplate setup by including 14 layers of the thin medium.

We report on the retrieval of the angular dependence of laser-induced electron rescattering in CO2 with a novel method from the measured rotational half revival signals of filed-free aligned molecules using a reaction microscope.

We report on efficient THz generation in DAST, driven by mid-infrared pump sources. Due to the suppression of multi-photon absorption, high pump fluences can be applied and outstanding optical to THz conversion efficiencies of more than 4% can be reached.

We present an energy-efficient and scalable technique to realize energetic sub-100-fs pulses, continuously tunable in the 1030÷1730 nm range, by exploiting stimulated Raman scattering in long N2-filled hollow-core fibers.

A conventional hollow-core fiber (HCF) scheme is implemented to investigate the effect of group velocity dispersion (GVD) and Raman scattering in spectral broadening in molecular gases for low energy pulse compression application.

In this paper, we demonstrate a pulse energy-governed nonlinear self-switching of femtosecond pulses at wavelength of 1700 nm in a highly nonlinear high index contrast dual-core fibre. The fibre structure is composed of two microdimension cores and a solid cladding made of two thermally matched soft glasses developed in-house. A double switching behaviour under monotonic increase of the input pulse energy from 1 nJ to 3 nJ was observed at 35 mm fibre length in its anomalous dispersion region. A spatial intensity distribution measurement identified a switching contrast of 16.7 dB, and the registered spectra of the two output channels revealed a broadband switching behaviour within 150 nm. The obtained results indicate a novel type of solitonic switching and represent a significant progress in comparison to the previous experimental works and has a high application potential.

We present strong field autocorrelation measurements of molecular ionization and dissociation with a reaction microscope. Time-frequency analysis of the time-domain signals was performed to obtain electron and nuclear dynamics during molecular ionization and dissociation.

A high harmonics source is used to perform x-ray resonant magnetic scattering on magnetic samples. The dynamics of laser-induced ultrafast demagnetization are probed and longer pump wavelengths are found to increase the initial quenching levels.

In this paper, we present an iterative learning algorithm for pulse-shape control applications of optical chirped pulse amplifiers for ultra-short, high-energy light pulses. For this, we first introduce a general nonlinear and infinite-dimensional mathematical model of chirped pulse amplifiers. By reducing the complexity of this detailed model and reformulating the control task, we are subsequently able to apply inversion-based iterative learning control to track desired output pulses. Using the reduced model to estimate both internal states and unknown parameters yields a fast and simple way of consistently estimating the input–output behavior without relying on a calibrated system model. The effectiveness of the resulting adaptive algorithm is finally illustrated with simulation scenarios on an experimentally validated mathematical model.

Zusammenfassung Die Beschreibung optischer Pulsverstärker für ultra-kurze Laserpulse resultiert in mathematisch aufwendigen, verteilt-parametrischen Modellen, deren detaillierte Modellierung und adaptive Regelung unlängst präsentiert wurde. In diesem Beitrag werden nun Aspekte der Identifikation geeigneter Parameter betrachtet, um ein gemessenes Eingangs-Ausgangs-Verhalten möglichst gut nachbilden zu können. Dazu werden effiziente Simulationsmodelle präsentiert, die den numerischen Aufwand – besonders bei hohen Wiederholraten und der dadurch auftretenden starken Verkopplung aufeinanderfolgender Pulse – in handhabbaren Grenzen halten.

We report on the results of a joint experimental and numerical study on the sub-cycle laser field-driven electron dynamics that underlie the population of highly excited electronic states in multiply ionized argon dimers by electron recapture processes. Our experiments using few-cycle laser pulses with a known carrier-envelope phase (CEP) in combination with reaction microscopy reveal a distinct CEP-dependence of the electron emission and recapture process and, furthermore, a small but significant CEP-offset to the scenario in which no excited argon dimers are produced. With the help of classical ensemble trajectory simulations we trace down these different CEP-dependencies to subtle differences in the laser-driven sub-cycle electron trajectory dynamics that involve in both cases the transfer of an electron from one argon ion across the system boundary to the neighboring ion and its transient capture on this ion.

We present experimental studies of long-distance transmission of ultrashort mid-infrared laser pulses through atmospheric air, probing air dispersion in the 3.6–4.2-μm wavelength range. Atmospheric air is still highly transparent to electromagnetic radiation in this spectral region, making it interesting for long-distance signal transmission. However, unlike most of the high-transmission regions in gas media, the group-velocity dispersion, as we show in this work, is anomalous at these wavelengths due to the nearby asymmetric-stretch rovibrational band of atmospheric carbon dioxide. The spectrograms of ultrashort mid-infrared laser pulses transmitted over a distance of 60 m in our experiments provide a map of air dispersion in this wavelength range, revealing clear signatures of anomalous dispersion, with anomalous group delays as long as 1.8 ps detected across the bandwidth covered by 80-fs laser pulses.

We report on an experimental and theoretical study of the ionization-fragmentation dynamics of argon dimers in intense few-cycle laser pulses with a tagged carrier-envelope phase. We find that a field-driven electron transfer process from one argon atom across the system boundary to the other argon atom triggers sub-cycle electron-electron interaction dynamics in the neighboring atom. This attosecond electron-transfer process between distant entities and its implications manifest themselves as a distinct phase-shift between the measured asymmetry of electron emission curves of the $\text{Ar}^{+}+\text{Ar}^{2+}$ and $\text{Ar}^{2+}+\text{Ar}^{2+}$ fragmentation channels. Our work discloses a strong-field route to controlling the dynamics in molecular compounds through the excitation of electronic dynamics on a distant molecule by driving inter-molecular electron-transfer processes.

We report on the unambiguous observation of the subcycle ionization bursts in sequential strong-field double ionization of H_{2} and their disentanglement in molecular frame photoelectron angular distributions. This observation was made possible by the use of few-cycle laser pulses with a known carrier-envelope phase, in combination with multiparticle coincidence momentum imaging. The approach demonstrated here will allow sampling of the intramolecular electron dynamics and the investigation of charge-state-specific Coulomb distortions on emitted electrons in polyatomic molecules.

Nonlinear (NL) interactions of strong THz electric and magnetic fields with matter are the next frontier in nonlinear optics. NL THz spectroscopy requires ultrashort/broadband THz pulses with high electric field strengths. Here, we report on THz generation from two-color laser filaments, driven by intense midIR pulses centered at $3.9 {\mu } \mathrm {m}$. We demonstrate generation of THz pulses with a spectral bandwidth of $\gt 15$ THz, extraordinary conversion efficiency of 2.34% and remarkably high energy of 0.185 mJ.

Optical Parametric Chirped-Pulse Amplification (OPCPA) is an emerging laser technology, providing a flexibility in operating wavelengths and power upscaling. Here, we investigate THz generation in organic crystals (DAST) by optical rectification (OR) of intense Mid-Infrared (MIR) pulses. The broadband spectrum exceeds several octaves when pumped by 100 fs, 3.9 μm OPCPA pulses. We report on an extraordinarily high THz energy density of 3.1 mJ/cm $^{\mathbf {2}}$ and crystal damage threshold $ {>}150$ mJ/cm $^{\mathbf {2}}$.

We demonstrate that intense free space THz fields can nonlinearly induce excitonic photoluminescence in room temperature semiconductors as well as cross-phase modulation in an electro-optic crystal.

A high harmonics source is used to perform x-ray resonant magnetic scattering on a magnetic sample. The dynamics of laser-induced ultrafast demagnetization are probed with respect to the wavelength of the pump beam. Longer pump wavelengths are found to increase the initial quenching levels.

Ultrafast laser sources operating in the mid-infrared spectral region, where many molecules and their functional groups have vibrational and rotational resonances, are very important tools for studying novel regimes of non-linear optics and strong field physics. Next to optical parametric amplifiers (OPAs) based on ZnGeP 2 (ZGP) crystals which, on the one hand, allow generation of energetic ultrashort mid-IR pulses at a mJ energy level, but, on the other, rely on complex and immature holmium pump lasers [1], a difference frequency generation (DFG) in AGS or GaSe crystals starting from a single broadband near-infrared (NIR) pulse [2] or via cascaded two-stage parametric down-conversion [3] is an alternative way to generate mid-IR pulses above 4-μm wavelength. In the later case more conventional Ytterbium, Neodymium or Ti:Saphire lasers are used to pump the frequency conversion stages. The use of a longer-wavelength 1.03 μm Ytterbium laser as compared to Ti:Sapphire pump sources yields an improved phase matching bandwidth, lower group velocity miss-match, as well as a lack of three-photon absorption, which reduces detrimental photo-darkening in AGS.

Nonlinear self-channeling (filamentation) of intense, ultrashort laser pulses in air has numerous potential applications ranging from remote sensing in the atmosphere to lightning control [1]. Recent progress in optical parametric chirped-pulse amplification (OPCPA) technology pushes the investigations of filamentation into short-wave infrared [2] and mid-wave infrared [3] regimes. At longer wavelengths, the propagation dynamics is affected by the presence of windows of anomalous dispersion due to the trace constituents of air [4,5]. Multiple odd harmonics of the infrared driver pulse can be easily detected and analyzed.

A generation of optical harmonics by circularly polarized light, which is in general forbidden in an isotropic medium, was recently observed in molecular gases where molecules were aligned and oriented by another linearly polarized laser pulse [1] or by pulses with twisted polarization [2]. In order to generate nth-harmonic with circularly polarized light, a molecule has to "absorb" n photons, having the same handedness, and to emit a single nth harmonic photon while fulfilling the energy and the momentum conservation laws, meaning a necessity to excite the molecule to appropriate rotational state. One can do this by means of intrapulse rotational Raman scattering, which prepares the molecule in the excited state through a subsequent absorption of (n-1) same-handed photons [1]. All previously reported experimental studies on circular harmonic generation in molecular gases were performed with visible/near-IR drivers, in either gas jets or in standing cells and with pre-alignment of molecules by an additional laser pulses. Here we report on the studies of self-action of elliptically polarized mid-IR pulses on the generation of low-order harmonics in filaments ignited in air and in argon, representing a molecular and an atomic gas respectively. The harmonics were driven by 20-mJ, sub-100 fs mid-IR pulses, centred at 3.9 pm wavelength. In the experiments filamentation was assisted by focusing light with a spherical mirror of ROC=-2500 mm into an open-end tube, through which Ar gas was flown at slight overpressure. Polarization of the pulses was controlled by a broadband quarter wave plate (QWP). Spectra of 5th and 7th harmonics were recorded after the filaments with a grating spectrometer (HR4000, OceanOptics). Polarization state of the generated harmonics was analysed with a Glan-Taylor polarizer.

Optical Parametric Chirped-Pulse Amplification (OPCPA) is an emerging laser technology, providing a flexibility in operating wavelengths and power upscaling [1]. In this work, we show that mid-IR OPCPA technology could overcome major challenges in enhancing intense broadband THz generation from organic crystals. Strong THz fields are presently under extensive research for its applications in particle accelerations and fundamental understanding of structural dynamics [2]. Currently, the most efficient technique relies on optical rectification (OR) of femtosecond near-IR OPA laser pulses (1.3–1.5 pm) in highly nonlinear organic crystals [3]. However, the technique is still limited to a few mJ of pump energies and organic crystals suffer from a relatively low damage threshold at this pump wavelength. To improve THz generation, it is therefore crucial to use alternative laser pump technologies, such as Cr-Forsterite lasers [4]. However, the associated pump wavelength of 1.25 pm typically leads to an increase in nonlinear absorption, which decreases the crystal damage threshold and lowers the effectively emitted THz spectral contents. Here, we used a high-energy OPCPA system with 3.9 pm central wavelength (20 Hz repetition rate) [1] to generate THz from DSTMS organic crystal (Swiss Terahertz LLC) by OR. The emitted spectrum is broad and extends beyond 5 THz (compared to 2 THz central frequency in the case of Cr-Forsterite pump [4]). In terms of conversion efficiency, we did not observe saturation up to energy fluence of 180–200 mJ/cm2. This is remarkably high as compared to the typical saturation values of sub-10 mJ/cm2 from both Cr-Forsterite and near-IR OPA pump systems [4]. We evaluated the damage threshold of DSTMS at 3.9 pm beyond 250 mJ/cm2, more than an order of magnitude higher than for alternative near-IR pump technologies. These two advantages, due to the small pump photon energies, which are much below the crystal band gap, allow overcoming the major challenge of technology-limited crystal size and address the experimental needs to high spectral contents.

We experimentally investigate dissociation of ${\mathrm{H}}_{2}^{+}$ in the (near-)zero proton energy region. Based on our experimental results we conclude that the underlying mechanism for the production of protons with such low energy in strong two-color and broadband laser fields is a stimulated Raman-scattering-based zero-photon-dissociation process, ${\mathrm{ZPD}}_{\text{stR}}$, taking place on the electronic ground state. It is furthermore shown that in the (near-)zero energy region the asymmetry in proton ejection induced by asymmetric laser fields is due to the interplay of several processes, rather than only pathway interferences, with vibrational trapping (or bond hardening) taking a key role.

Fiber-optic multioctave supercontinuum generation is a unique resource for ultrafast optical science, enabling ultrabroadband frequency-comb technologies and paving the way for the photonics of subcycle field wave forms. Extension of these methods to the midinfrared spectral range encounters numerous challenges, calling for radically new approaches in fiber optics and short-pulse generation technologies, as well as for closing the gaps in our understanding of optical nonlinearities in the midinfrared range. Here, we confront these challenges by showing that multioctave supercontinua spanning from the ultraviolet to the midinfrared range can be generated by shock-wave-coupled soliton self-compression of ultrashort midinfrared pulses in a gas-filled antiresonance-guiding hollow-core photonic-crystal fiber. Analysis of the fiber output spectra, measured within a broad range of gas pressures and input driver energies, shows that multioctave supercontinuum generation in this setting becomes possible due to soliton self-compression coupled to shock-wave pulse self-steepening, yielding extraordinarily short, sub-half-cycle field transients.

We demonstrate two-dimensional control over the chargelocalization in H2 dissociation using elliptically polarized laser pulses. The influences of the CEP and the laser phase at the instant of ionization are investigated.

We examine mid-IR light bullets generated in ambient air. 2-optical cycle pulses confined in space are generated in filamentation regime. Few-fold solitonic self-compression is achieved for strongly chirped mid-IR pulses.

We generate fully controllable fs multimillijoule pulse bursts with the energy handling, throughput efficiency and frequency resolution substantially exceeding that achievable in spatial-light-modulator and interferometric techniques. The demonstrated proof-of-concept experiments include coherent control of nitrogen-ion emission via multiple-pulse excitation and generation of tunable narrowband THz pulses via optical rectification.

We introduce and employ the molecular attoclock method. This allows us to simultaneously trace the nuclear and electron dynamics during H2 fragmentation, and to CEP-control the two-electron emission dynamics on sub-cycle time scales., High Intensity Lasers and High Field Phenomena, 26–28 March, 2018, Strasbourg, France

In this work we present a route for energy scaling in external pulse compression based on layered Kerr media combined with 1D focusing geometry. A highly stable 92%-efficient 4-fold compression of 1030-nm pulses is demonstrated.

Using a gas-filled stretched HCF post-compressor, we demonstrate the generation of 25 fs, 40 mJ pulses at 1 μm wavelength for noble gases and a smooth wavelength tunability up to 1.3 μm for molecular gases.

We report on THz generation driven by 3.9 µm pulses, via either optical rectification in organic crystals or in two-color plasma filaments. Outstanding THz conversion efficiency of more than 2% and bandwidth exceeding 15 THz are achieved.

In this Letter, we investigate the energy-scaling rules of hollow-core fiber (HCF)-based nonlinear pulse propagation and compression merged with high-energy Yb-laser technology, in a regime where the effects such as plasma disturbance, optical damages, and setup size become important limiting parameters. As a demonstration, 70 mJ 230 fs pulses from a high-energy Yb laser amplifier were compressed down to 40 mJ 25 fs by using a 2.8-m-long stretched HCF with a core diameter of 1 mm, resulting in a record peak power of 1.3 TW. This work presents a critical advance of a high-energy pulse (hundreds of mJ level) nonlinear interactions platform based on high energy sub-ps Yb technology with considerable applications, including driving intense THz, X-ray pulses, Wakefield acceleration, parametric wave mixing and ultraviolet generation, and tunable long-wavelength generation via enhanced Raman scattering.

A robust Ho:YAG chirped pulse amplifier with a simple dispersion management was developed for material processing applications. The amplifier produces 3.2 ps pulses centered at 2.09 μm with energies up to 1.6 mJ. At 10 kHz repetition rate this results in 16 W of average power. Both pulse stretching and compression in the amplifier is realized within a single chirped volume Bragg grating. With the developed amplifier we study laser ablation of a gold layer through a carrier substrate and, particularly, the effect of pulse duration on the process. A balance between nonlinear effects within the carrier and interaction with the thin ablation layer makes few picosecond pulses most suitable for non-thermal ablation. Furthermore, since only a few-microjoules of pulse energy is required for de-bonding, the developed 16 W amplifier can be potentially operated at MHz repetition rates for high throughput.

International audience; We present an infrared source operating at 1937 nm center wavelength capable of generating 1.35 mJ pulse energies with 1 kHz repetition rate and 2 GW peak power based on a diode-pumped Tm:YAP regenerative amplifier. The obtained pulses after 45 round trips have been compressed down to 360 fs. Using only a small portion (15 µJ) of the output of the system we managed to generate a white light continuum in a 3 mm YAG window that exhibits the viability of the system as a suitable candidate for a pumping source of a mid-infrared optical parametric amplifier.

Physical review / X Expanding access X 9(2), 021029 (2019). doi:10.1103/PhysRevX.9.021029, We report on experimental results in a new regime of relativistic light-matter interaction employing midinfrared (3.9-mu m wavelength) high-intensity femtosecond laser pulses. In the laser-generated plasma, electrons reach relativistic energies already for rather low intensities due to the fortunate lambda(2) scaling of the kinetic energy with the laser wavelength. The lower intensity efficiently suppresses optical field ionization and creation of the preplasma at the rising edge of the laser pulse, enabling an enhanced efficient vacuum heating of the plasma. The lower critical plasma density for long-wavelength radiation can be surmounted by using nanowires instead of flat targets. Numerical simulations, which are in a good agreement with experimental results, suggest that approximate to 80% of the incident laser energy has been absorbed resulting in a long-living, key-temperature, high-charge-state plasma with a density more than 3 orders of magnitude above the critical value. Our results pave the way to laser-driven experiments on laboratory astrophysics and nuclear physics at a high repetition rate., Published by APS, College Park, Md.

We demonstrate the simultaneous generation of second, third, and fourth harmonic from a single dielectric Bismuth Ferrite nanoparticle excited by a telecom fiber laser at 1560 nm. We first characterize the signals associated with different nonlinear orders in terms of spectrum, excitation intensity dependence, and relative signal strengths. Successively, on the basis of the polarization-resolved emission curves of the three harmonics, we discuss the interplay of susceptibility tensor components at the different orders and we show how polarization can be used as an optical handle to control the relative frequency conversion properties., Comment: include S.I. section at the end of the main pdf file

We demonstrate narrow band spectral intensity switching in dual-core photonic crystal fibers made of highly nonlinear glass under femtosecond excitation. The fibers expressed dual-core asymmetry, thus the slow and fast fiber cores were unambiguously distinguished according to their dispersion profiles. The asymmetry effect on the dual-core Propagation in anomalous dispersion region was studied both experimentally and numerically. The experimental study was carried out using femtosecond laser amplifier system providing tunable pulses in range of 1500 nm - 1800 nm. The obtained results unveiled, that it is possible to improve nonlinearly the coupling between the two waveguides by excitation of the fast fiber core. The results were obtained in regime of high-order soliton propagation and were verified numerically by the coupled generalized nonlinear Schrodinger equations model. The spectral analysis of the radiation transferred to the non-excited core revealed the role of effects such as third order dispersion, soliton compression and spectral dependence of the coupling efficiency. The simulation results provide reasonable agreement with the experimentally observed spectral evolutions in the both fiber cores. Under 1800 nm excitation, narrow band spectral intensity switching was registered with contrast of 23 dB at 10 mm fiber length by changing the excitation pulse energy in sub-nanojoule range.

We present high flux table-top 220eV HHG source (>109 photons/s/1% bandwidth) driven directly by a

Burst-mode regenerative amplifiers permit substantial energy and average-power scaling of pump lasers. We demonstrate advantages of parametric burst-to-single-pulse up- and down-conversion in the generation of optical harmonics and in multicolor pumping of long-wave parametric amplifiers.

We experimentally achieve two-dimensional CEP-control of bond breaking in H2 dissociation with elliptically polarized pulses. The lab and molecular frame of reference proton ejection asymmetries are compared.

We report kinematically complete measurements of frustrated double ionization of argon atoms with a reaction microscope. Experimental results show much higher electron trapping probability during the strong-field double ionization than that during the single ionization.

Physical review letters 120(9), 093002 (2018). doi:10.1103/PhysRevLett.120.093002, Recent advances in high-order harmonic generation have made it possible to use a tabletop-scale setup to produce spatially and temporally coherent beams of light with bandwidth spanning 12 octaves, from the ultraviolet up to x-ray photon energies >1.6 keV. Here we demonstrate the use of this light for x-ray-absorption spectroscopy at the K- and L-absorption edges of solids at photon energies near 1 keV. We also report x-ray-absorption spectroscopy in the water window spectral region (284–543 eV) using a high flux high-order harmonic generation x-ray supercontinuum with 10$^9$ photon/s=s in 1% bandwidth, 3 orders of magnitude larger than has previously been possible using tabletop sources. Since this x-ray radiation emerges as a single attosecond-to-femtosecond pulse with peak brightness exceeding 10$^{26}$ photon$/s/mrad^{2}/mm^{2}/1$% bandwidth, these novel coherent x-ray sources are ideal for probingthe fastest molecular and materials processes on femtosecond-to-attosecond time scales and picometer length scales., Published by APS, College Park, Md.

We demonstrate an efficient difference frequency generation in the 5-11 μm spectral range. A KTA-AGS based parametric source is driven by 14 mJ Yb:CPA and provides 150 μJ pulses with up to 3 μm bandwidth.

We demonstrate kinematically complete measurements on frustrated double ionization of argon atoms in strong laser fields with a reaction microscope. We found that the electron trapping probability after strong field double ionization is much higher than that after strong field single ionization, especially in case of high laser intensity. The retrieved electron momentum distributions of frustrated double ionization show a clear transition from the nonsequential to the sequential regime, similar to those of strong field double ionization. The dependence of electron momentum width on the laser intensity further indicates that the second released electron has a dominant contribution to frustrated double ionization in the sequential regime.

We report results of experimental investigation on polarization evolution and losses in linearly and circularly polarized mid-IR filaments in air under different focusing conditions.