Simulation of self-focusing of femtosecond laser pulses in air by the method of diffraction beams and light tubes
The results of a theoretical investigation of the propagation of femtosecond pulses of a Ti:Sapphire laser in air during the self-focusing and filamentation are presented. The analysis of self-focusing of laser pulses was carried out on the basis of the method of diffraction beams and light tubes, which made it possible to establish that specific light structures are formed in the laser beam during self-focusing. One of such structures is the energy-replenishing diffraction-beam tube, which provides necessary energy for filamentation, and at the stage of post-filamentation pulse propagation exists in the form of a separate intense light channel. The dependences of the radius and power of the energy-replenishing tube on the initial beam radius and the peak power for a fixed pulse duration are established. It was revealed that the energy consumption of radiation per filamentation decreases with an increase in the beam radius and a decrease in its initial power. The peak power contained in the energy-replenishing light tube at the post-filamentation propagation stage of laser pulses does not exceed the critical self-focusing power for the Gaussian beam and weakly depends on the initial parameters of the pulse.