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We present a detailed experimental and numerical study of supercontinuum generation in sapphire crystal at the vicinity of its zero group velocity dispersion point (1.3 μm) when pumped by relatively long (210 fs) femtosecond pulses. We uncover very different evolutions of the spectral broadening versus the input pulse energy when the incident beam is focused either onto the input face or inside the 4-mm-thick sapphire sample. In particular, when the input beam was focused inside the crystal, we captured a surprising variation of the spectral width as a function of the input pulse energy, demonstrating supercontinuum generation, its suppression, and eventually, its recovery. The experimental findings were nicely reproduced by the numerical simulations, revealing a specific supercontinuum generation scenario, which relies on strong reshaping of the wave packet due to defocusing and absorption of free electron plasma, subsequent replenishment of the pulse on the propagation axis, and its splitting. We also demonstrate that this particular supercontinuum generation scenario takes place regardless of the external focusing geometry.

International audience; We report on generation of ultrabroadband, more than 4 octave spanning supercontinuum in thin CaF2 crystal, as pumped by intense mid-infrared laser pulses with central wavelength of 2.4 μm. The supercontinuum spectrum covers wavelength range from the ultraviolet to the mid-infrared and its short wavelength side is strongly enhanced by cascaded generation of third, fifth and seventh harmonics. Our results capture the transition from Kerr-dominated to plasma-dominated filamentation regime and uncover that in the latter the spectral superbroadening originates from dramatic plasma-induced compression of the driving pulse, which in turn induces broadening of the harmonics spectra due to cross-phase modulation effects. The experimental measurements are backed up by the numerical simulations based on a nonparaxial unidirectional propagation equation for the electric field of the pulse, which accounts for the cubic nonlinearity-induced effects, and which reproduce the experimental data in great detail.

International audience; We study the propagation of intense, high repetition rate laser pulses of picosecond duration at 1.03 µm central wavelength through air. Evidence of filamentation is obtained from measurements of the beam profile as a function of distance, from photoemission imaging and from spatially resolved sonometric recordings. Good agreement is found with numerical simulations. Simulations reveal an important self shortening of the pulse duration, suggesting that laser pulses with few optical cycles could be obtained via double filamentation. An important lowering of the voltage required to induce guided electric discharges between charged electrodes is measured at high laser pulse repetition rate.-repetition-rate picosecond pump laser based on a Yb:YAG disk amplifier for optical parametric amplification

We analyze numerically and experimentally the effect of the input pulse chirp on the nonlinear energy deposition from $5\ \mu$J fs-pulses at $800$ nm to water. Numerical results are also shown for pulses at $400$ nm, where linear losses are minimized, and for different focusing geometries. Input chirp is found to have a big impact on the deposited energy and on the plasma distribution around focus, thus providing a simple and effective mechanism to tune the electron density and energy deposition. We identify three relevant ways in which plasma features may be tuned., Comment: 9 pages, 7 figures

We report on the generation of ultrabroadband supercontinuum (SC) by filamentation of two optical-cycle, carrier-envelope phase-stable pulses at 2 μm in fused silica, sapphire, CaF₂ and YAG. The SC spectra extend from 450 nm to more than 2500 nm, and their particular shapes depend on dispersive properties of the materials. Prior to spectral super-broadening, we observe third-harmonic generation, which occurs in the condition of large phase and group velocity mismatch and consists of free and driven components. A double-peaked third-harmonic structure coexists with the SC pulse as demonstrated by the numerical simulations and verified experimentally. The SC pulses have stable carrier envelope phase with short-term rms fluctuations of ∼ 300 mrad, as simultaneously measured in YAG crystal by f-2f and f-3f interferometry, where the latter makes use of intrinsic third-harmonic generation.

In this paper the results of the theoretical and experimental study of spatiotemporal distortions emerging in noncollinear optical parametric chirped-pulse amplifiers are presented. In a noncollinear parametric amplifier, when the pulse fronts of the pump and signal are not matched, the signal pulse becomes tilted and, aside from angular dispersion, has a spatial chirp. The expressions relating the magnitudes of the acquired spatial chirp and angular dispersion to the temporal chirp of the signal pulse are derived. It is shown that the magnitudes of the induced spatial chirp and angular dispersion decrease at different rates with the increase of the signal pulse temporal chirp and, for the large temporal chirp, the spatial chirp mainly contributes to the pulse-front tilt of the signal, whereas the induced signal pulse tilt is independent of the signal pulse temporal chirp, but is always smaller than the tilt of the pump pulse.