Diffraction-Ray Model of Single Filamentation of Femtosecond Laser Pulses for Estimating the Characteristics of the Multiple Filamentation Domain in Air

The characteristics of the multiple filamentation domain of femtosecond laser pulses in air have been estimated based on the single filamentation model. The diffraction-ray model is considered as the single filamentation model. It is based on representation of a laser beam by a set of diffraction-ray tubes nested into each other that do not intersected in space and do not exchange by their energies. In this situation, changes in the tube shapes and cross sections during beam propagation demonstrate the effect of physical processes that occur with radiation in the medium. It is shown that this model is efficient for interpreting experimental results. In particular, it has been demonstrated that the radius of small-scale intensity inhomogeneities in the profile of a centimeter laser beam forming the multiple filamentation domain of subterawatt femtosecond laser pulses is several millimeters. The power in these inhomogeneities varies from several units to several tens of gigawatts. Telescoping the initial laser beam that caused an increase in its radius also increased sizes of the initial smallscale intensity inhomogeneities and decreased the power contained in them. As a result, the coordinate of the filamentation onset is shifted along the propagation path from the laser pulse source. The lengths of the filaments and their number increase with the peak beam power.