Nonlinear-optical transformation of a high-power femtosecond laser pulse in air

A change in the spectrum and the energy distribution of the light field of a high-power femtosecond laser pulse is studied numerically in a broad range of its spatial scales. It is shown that the effect of filamentation, the generation of a supercontinuum and conical emission, the formation of a ring structure in the distribution of the pulse energy and other effects observed during the propagation of the laser pulse in air are caused by the nonlinear-optical transformation of the light field in the region with dimensions exceeding substantially the transverse size of the filament. The pulse filamentation is accompanied by the redistribution of power in its cross section. The spatio – temporal characteristics of emission calculated for femtosecond laser systems are in quantitative agreement with the experimental data.