Thermal self-action of high-power continuous and pulse-periodic CO2 laser radiation in air: II. Laboratory experiments

Abstract

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.