Integral parameters of high-power femtosecond laser radiation during filamentation in air

The main effective parameters of high-power femtosecond laser radiation (energy transfer coefficient, effective radius, effective duration, limiting angular divergence, and effective intensity) during its propagation along an atmospheric horizontal path under the conditions of filamentation have been investigated theoretically. It is shown that the process of self-action of this radiation is characterized by formation of a nonlinearity layer, after which the radiation propagates linearly with the limiting divergence lower that the initial diffraction-limited divergence of the beam. The effective pulse duration and the effective beam radius increase after the passage through the nonlinearity layer, and their values are mostly determined by the initial beam power and weakly depending on the initial spatial focusing of the beam. The coefficient of energy transmission for the femto-second pulse is lower than in the linear medium and has a tendency to decrease with the increase of the power.