The results of experimental and theoretical studies of the evolution of the small-scale transverse structure of high-power femtosecond laser radiation propagating in air in the multiple filamentation mode are presented. It has been found that the presence of intensity inhomogeneities in the initial transverse profile of a laser beam leads to the formation of high-intensity light channels due to the Kerr-induced self-focusing effect. When the power in these channels exceeds a certain threshold value (the critical power), the filamentation in these structures is implemented. Parameters of these light channels are theoretically estimated on the basis of the diffraction-ray model of single filamentation. It is shown that the initial radius of intensity inhomogeneities in the transverse profile of a laser beam with a centimeter radius and subterawatt power is of characteristic value of several millimeters.
femtosecond laser pulse, air, filamentation, light channels, diffraction-ray tube
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