D. V. Apeksimov

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.

Filamentation length of high-power sharply focused femtosecond laser radiation in air. Effect of light beam size

The results of laboratory experiments on measurements of the length and position of the filamentation zone of femtosecond GW laser radiation at wavelengths of 800 and 400 nm propagating in air under conditions of sharp external focusing are presented. Dependencies of the length of the radiation filamentation zone on its initial radius and power are studied. Qualitatively new regularity is obtained, which consists in invariance of the observed length of the beam filamentation under variations in its diameter with the assumption of equality of the initial intensities. The feature is not typical for collimated radiation and is connected with the dominance of geometrical focusing over Kerr self-focusing of a beam during filament formation.

Filamentation of non-Gaussian laser beams with different geometric divergence along an atmospheric path

The results of atmospheric experiments on the propagation of femtosecond IR laser pulses with a complex initial transverse profile of intensity under self-focusing and filamentation conditions are presented. The effect of the initial geometric divergence of radiation on the transverse structure of light energy in a beam at the end of a path is studied. Numerical simulation of the problem is carried out, and parameters of the generated filaments and plasma channel are determined. It is shown that geometric focusing or defocusing of radiation allow moving the nonlinear focus and the related filamentation region along the path in sufficiently wide limits.

Effective parameters of terawatt femtosecond laser radiation on a horizontal atmospheric path

Angular and spectral effective parameters of intense chirped femtosecond laser radiation upon the propagation on an open atmospheric path under conditions of self-focusing and filamentation depending on the initial energy of laser pulse are experimentally investigated. The regime when an initially highly aberrational laser beam forms a steady spatial configuration of the filaments, whose number is defined by the energy of radiation, is studied. The results of numerical calculations of a nonstationary laser beam that is self-focusing in air with a multimodal transversal intensity profile, which has a qualitatively interpret experimental data, are presented.

Debye potentials for heterogeneous media

The paper presents the results of the Helmholtz equation solution by the method of perturbation theory in the spherical coordinate system for the Debye potentials for weakly heterogeneous media based on metal nanoparticles and the dielectric matrix. In that case, the dielectric function of a composite changes in space in the radial direction.

Scattering properties of a radially heterogeneous sphere made of metal nanoparticles and the dielectric matrix

The cross-sections of attenuation, scattering and absorption of spherically aggregated metal nanoparticles in dependence on the aggregate size, the degree of its filling with nanoparticles and physical properties of nanoparticle material have been estimated, according to the model of the effective medium and the theory of G. Mie. In that case, the concentration of the nanoparticles changes radially.

Modeling of multiple filamentation of terawatt laser pulses on a hundred-meter air path

The results of numerical simulation of multiple filamentation of terawatt femtosecond pulse Ti:Sapphire laser performed on the experimental data obtained in the airway of a length of 106 m when changing the initial spatial focusing and laser power.

Frequency-pulsed regime of excitation of spherical microcavity by chirp ultra-short laser radiation

The numerical simulations results of resonance excitation of internal optical field of transparent spherical microparticles under irradiation by ultra-short laser pulse train are presented. It was determined that the most optimal tuning of incident radiation to assigned high-Q eigenresonance of a particle might be realized using varying a porousness of pulse in a train with linear frequency modulation of each pulse in a train (chirping). Analytical expressions were found for calculation of these parameters depending on laser pulse duration and frequency location of excited resonance.