Results of laboratory experiments on nonlinear propagation of high-power pulse-periodic and continuous CO₂ laser radiation in a gas medium are presented. The experiments were carried out in a cell filled with a mixture of air and carbon dioxide in different partial concentrations (∼1–4%) under strong absorption and thermal blooming of laser radiation. The experimental conditions simulated the atmospheric propagation of high-power laser radiation along a kilometer-long path. Sharply focused laser beams were used; the regions of heat release along the beam channel were recorded by the shadow imaging technique. We found that, despite increased intensity, the focal waist of a laser beam is characterized by reduced heat release as compared to that in the pre- and postfocal beam regions. The saturation effect of the resonance absorption coefficient of CO₂ at high pulse peak intensity (blooming effect) is considered as the most probable physical cause of the above feature. For continuous radiation, this effect is much weaker.

A class of energy light structures in nonlinear wave physics, so-called diffraction-beam tubes in a self-focusing dissipative medium, has been studied. It is shown that their interaction along a high-power femtosecond laser radiation propagation path produces areas of light energy localization, stable in physical characteristics, i.e., a filament and a post-filamentation channel, as well as an energy-conservative periphery. Stabilization of boundaries of the above areas is provided by additional contraction of a diffractive nature from the side of the periphery. The dependencies of filamentation length of a laser pulse on the power and beam radius and the fact of high intensity conservation in the post-filamentation light channel are interpreted using this concept.

The results are presented of experiments on controlling the characteristics of the multiple filamentation domain of femtosecond laser pulses along atmospheric paths via variations in the initial spatial focusing, beam radius, and pulse energy, as well as the optical field structure at the initial beam aperture.

Possible thermodynamic trajectories of an overheated fluid in zones of the plasma formation of a water particle are constructed and analyzed to determine the dynamics of the phase state of the matter. The mass fraction of steam generated during the explosive boiling of different drop parts is estimated.