The effect of local heterogeneities of the medium along the propagation path of high power femtosecond laser pulses on the generation of electromagnetic radiation at shifted wavelengths

The report presents the results of studies of filamentation of femtosecond laser pulses in the presence at the beginning of the propagation path of a layer with a randomly inhomogeneous refractive index formed by a stream of hot air directed perpendicular to the direction of radiation propagation. It is shown that this technique of forced initiation of inhomogeneities in the transverse energy structure of a laser beam leads to the formation of high-intensity light sub-beams, which, unlike low-intensity narrow beams, are not blurring at short distances due to the large diffraction divergence, while maintaining a small diameter and, consequently, intensity over long distances due to the implementation of Kerr nonlinearity in the medium. Such preliminary segmentation of high-power laser radiation leads to a multiple increase in the number of high-intensity slightly divergent light channels, the characteristic intensity of which is sufficient to realize two-photon absorption in the volume of aerosol particles, which in turn significantly increases the magnitude of the fluorescence signal detected by the lidar circuit. In addition, it is shown that the turbulent layer formed at the beginning of the optical path makes it possible to increase the efficiency of THz radiation generation from the filamentation region by up to 1.5 times due to the formation of a multitude of randomly arranged filaments resulting from random perturbations of the energy profile of the optical beam.