V. K. Oshlakov

Filamentation of a sharply focused ultrashort laser pulse at wavelengths of 800 and 400 nm: Measurements of the nonlinear index of air refraction

We present the results of experimental investigations of the filamentation dynamics of high-power ultrashort Ti:Sapphire-laser pulses with wavelengths of 800 and 400 nm with their sharp focusing in air. The dependences of position and dimensions of a plasma channel generated in the nonlinear beam focus zone on the laser pulse power are obtained. The effective value of the nonlinear index of air refraction related to the optical Kerr effect is determined for two laser wavelengths from processing of the dependences when using laser radiation self-focusing theory.

Filamentation of the focused Ti: Sapphire laser pulse in air at two harmonics

The results of experiments on the filamentation dynamics of high-power ultrashort Ti: sapphire laser pulses with wavelengths of 800 and 400 nm upon their sharp focusing in air are presented. The dependences of the position and dimensions of the plasma channel that forms in the region of the nonlinear beam focus on the laser pulse power are obtained. The spectra of the laser pulse during its filamentation are measured.

Interaction between gigawatt laser pulses and liquid media: Part 1. Explosive boiling of large individual water droplets

The results of experiments on femtosecond GW laser pulse interaction with isolated millimeter-size water droplets are presented. The temporal and spatial dynamics of optical breakdown in a liquid particle is investigated. The mechanical fragmentation of the droplet as a result of the evaporation and explosion of superheated areas is also discussed. The spectral characteristics of water particle glow during its explosive boiling are investigated.

Multiple filamentation of collimated laser radiation in water and glass

Results of an experimental study of spatial parameters of the region of multiple filamentation of gigaand terawatt pulses of a Ti:Sapphire laser in glass and water are described. The pulse-power dependencies of the coordinates of the filamentation region, the number of filaments, their distribution along the laser beam axis, and the mean length of the filaments are presented. It is shown that the spatial parameters of the filamentation region are qualitatively similar in water and glass. It is found that the number of filaments along the region of multiple filamentation is a unimodal distribution. When increasing the radiation power, the length of individual filaments in the region of multiple filamentation is reduced, and their diameters are quasi-constant at all power values implemented in the experiment. When attaining a certain power of laser pulses with a Gaussian energy-density distribution, the filamentation region takes the shape of a hollow cone with the apex directed to the radiation source.

Filamentation of terawatt laser pulses along hundred-meter atmospheric paths

Results of the experimental study of filamentation of terawatt femtosecond pulses of a Ti:Sapphire laser along an atmospheric path 106 m long using different spatial focusing and pulse power are presented. The control of filamentation region position and length by means of changing the initial laser beam focusing is shown to be highly effective. Dependencies are derived of filamentation region position and length on the initial degree of focusing, pulse power, and the number of filaments along the filamentation region. The obtained data on the filamentation region length and the number of filaments are compared with the results of our previous experiments and data from other authors.

Filamentation of femtosecond Ti:Sapphire laser pulses at the first and second harmonics in liquid media

The experimental results on transformation of the spectral and spatial characteristics of femtosecond Ti:Sapphire-laser pulses with wavelengths of 800 and 400 nm during filamentation in liquid media are presented. It is shown that spectral broadening of a laser pulse at both harmonics at the expense of phase self-modulation in a medium with cubic nonlinearity depends on pulse power and beam diameter. Emission with a maximum at 464 nm is observed during filamentation of the pulses with a wavelength of 400 nm in distilled water, which corresponds to stimulated Raman scattering of the water. Fluorescence of dissolved organic matter is observed in sea water.

Interaction of GW laser pulses with liquid media. Part 2. Spectral and angular characteristics of scattering by millimeter water droplets

We present the results of experimental investigations of interaction between femtosecond laser pulses of gigawatt power and suspended distilled water droplets of millimeter size. The angular distribution of the spectral characteristics of water particle emission is investigated.

Multiple filamentation of laser beams of different diameters in air along a 150-meter path

Results of experiments on controlling the position and length of the filamentation region of femtosecond laser pulses along atmospheric paths 150 m long using different initial spatial focusing and defocusing are presented. The distribution of filaments over the filamentation region is found; the dependencies of the length of the filamentation region on the numerical aperture of a beam, its initial radius, and pulse power are derived. Emission spectra of targets made of different materials and placed in the filamentation region far from the radiation source are measured.

Multiple filamentation of collimated Ti:Sapphire laser beams in water

The results of experimental studies of femtosecond laser pulse filamentation in water are described. The dependencies of the number of filaments, spectrum width, distance of nonlinear focusing, and diameter of filamentation zone on the laser pulse power are measured. Existence of a segment on the scale of relative power is marked out, where the number of filaments increases dramatically.

Experimental study of the interaction between terahertz radiation from the Novosibirsk free-electron laser and water aerosol

Interactions of high-power terahertz radiation from the Novosibirsk free-electron laser at a wave-length of 130 µm in an atmospheric window with a model aerosol cloud with a known droplet size distribution function has been studied experimentally for the first time. The experimental data are compared with theoretical calculation results obtained from solution of the lidar equation for conditions of the experiment.