Filamentation of high-power femtosecond laser pulses in air is accompanied by a fairly strong release of optical energy into the propagation medium due to laser-induced ionization of air molecules and production of an underdense plasma of charged species. We present the results of our laboratory experiments and numerical simulations aimed at estimating the energy deposition amount by laser filament upon propagation in air depending on the conditions of spatial focusing, pulse energy, and radiation wavelength. Importantly, our study reveals a more than 50% decrease in the filament energy deposited in air in the range of moderate numerical aperture values, approximately from 0.003 to 0.007, at carrier wavelengths of 740 and 470 nm. We attribute such a considerable reduction in the laser pulse energy release for femtosecond plasma to the competing effects of Kerr self-focusing and geometric divergence of focused laser pulse.

The spectrum transformation of a femtosecond wave packet during filamentation in fused silica under conditions of normal, zero, and anomalous group velocity dispersion has been investigated using numerical simulation methods. It has been shown that the generation of plasma, which induces phase modulation of the light field, leads to rapid anti-Stokes spectral broadening. It has been established that the short-wavelength shift of the broadband supercontinuum spectrum is significantly greater under anomalous group velocity dispersion compared to normal and zero dispersion. The influence of the wave packet energy on the dynamics of spectral broadening has been examined. Estimates of the numerical scheme have been obtained based on dispersion analysis of the broadband supercontinuum propagation process in the medium.

We use time-resolved spectral probing to study the dynamics of transformation of the optical properties of a nonlinear medium during formation and propagation of an extremely compressed mid-IR femtosecond wave packet in calcium fluoride. Broadening, attenuation and distortion of the probe pulse spectrum have been experimentally observed varying the delay time of the probe pulse relative to the pump. By solving the unidirectional pulse propagation equation that describes propagation and filamentation of a pump pulse in a calcium fluoride crystal we determine temporal changes of the refractive index and absorption coefficient induced by an extremely compressed wave packet. A mechanism of the observed broadening and breakup of the probe pulse spectrum is proposed.

This paper presents the results of experimental and numerical study of the anti-Stokes wing formation and the evolution of the short-wavelength cutoff in the 1900 nm pulse spectrum during its propagation and filamentation in fused silica and calcium fluoride. It is found that during the light bullet formation the short-wavelength cutoff in the supercontinuum spectrum is shifted to the anti-Stokes region with an increase in the nonlinear optical interaction length with the medium. However, change in the short-wavelength cutoff in the formed light bullet spectrum throughout its further propagation is insignificant.