V. Jukna

Ultrabroadband supercontinuum and third-harmonic generation in bulk solids with two optical-cycle carrier-envelope phase-stable pulses at 2 μm

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.

Spatiotemporal rogue events in femtosecond filamentation

We present experimental and numerical investigations of optical extreme (rogue) event statistics recorded in the regime of femtosecond pulse filamentation in water. In the spectral domain, the extreme events manifest themselves as either large or small extremes of the spectral intensity, justified by right- or left-tailed statistical distributions, respectively. In the time domain, the observed extreme events are associated with pulse splitting and energy redistribution in space and therefore are exquisitely linked to three-dimensional, spatiotemporal dynamics and formation of the X waves.

Rogue-wave-like statistics in ultrafast white-light continuum generation in sapphire.

We experimentally study the statistics of the white-light continuum generated by focusing of 130 fs, 800 nm pulses in a sapphire plate and show that the statistical distributions of the spectral intensity of the blue-shifted continuum components obey the extreme-value statistics. This rogue-wave-like behavior is detected only within a narrow input-pulse energy interval. By the use of numerical simulations, we show that the observed rogue-wave-like behavior is associated with pulse splitting and build-up of intense trailing pulse. The extreme events are thereafter suppressed by the intensity clamping.

Manifestation of spatial chirp in femtosecond noncollinear optical parametric chirped-pulse amplifier

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.

Spatio-temporal rogue events in femtosecond filamentation

Optical rogue waves, recently discovered by Solli et al. [1] constitute a fascinating topic in modern nonlinear optics. Until now, most of the knowledge on optical rogue waves is brought by the studies of supercontinuum generation in optical fibers under different operating conditions. However extreme-value statistics, the most prominent manifestation of rogue waves, is also inherent to various nonlinear optical systems, and to ultrashort pulse filamentation in particular [2].

Spatial chirp and angular dispersion dynamics in femtosecond noncollinear OPCPA

We present the results of theoretical, numerical and experimental study on transformation of chirped pulse spatio-temporal characteristics, when pump and signal pulse fronts are not matched during the amplification in noncollinear optical parametric chirped-pulse amplifier.

Self-phase matching and X pulse formation in phase-mismatched second harmonic generation due to dimensionality transition

Since 1961, when Franken and his collaborators experimentally discovered second-harmonic generation (SHG) [1], the process of SHG has been widely investigated leading first to important contributions by many authors, who derived the now well-known theory described in nonlinear optics books. It was realized long time ago that the use of short light pulses for SHG gives rise to special effects, like the broadening of the generated light pulse due to the group velocity mismatch between the fundamental (FH) and second-harmonic (SH) pulses, predicted by Comly and coworkers [2] and observed for the first time by Shapiro [3]. Typically SHG is investigated or used at or near the phase-matching condition, in such a way to maximize the conversion efficiency. More recently the study of propagation phenomena in phase-mismatched second-harmonic processes has attracted considerable interest, in particular for the investigation of the effect on the generated pulse shape. However, typically mentioned studies were done in the case when the plane wave approximation is valid and SHG could be recognized as one-dimensional problem.

Generation of periodic filament arrays by self-focusing of highly elliptical ultrashort pulsed laser beams

Powerful ultrashort laser pulses reveal surprising features on the nature of light and matter interactions. Intense optical field modifies the refractive index of the medium through the optical Kerr effect and gives rise to self-focusing, self- and cross-phase modulation, spectral broadening, electron plasma generation, etc. The phenomenon, which couples these effects as a whole, is called femtosecond filamentation [1]. High-power laser beams break-up into multiple filaments (MFs) [2]. This process is governed by the growth of the wave-front perturbations that lead to random filament distribution over a given transverse plane. However, most of the applications require precise filament localization, and high MF pattern reproducibility is of paramount importance.