Beam breakup and filament initiation induced by femtosecond pulse transmission through water aerosol

Abstract

Propagation of high-power femtosecond laser pulse through random media is accompanied by transverse spatial distortions of the laser beam. Occurrence of high-intensity small-scale perturbations due to atmospheric disturbance may result in beam breakup and filament generation. Coherent scattering on random ensemble of aerosol particles result in these disturbance. On the other hand, plasma formation, owing to focusing of light into aerosol microdroplet, may hinder filamentation. The purpose of this paper is to numerical study the propagation of a femtosecond laser pulse through water aerosol. In particular, we will find the transverse intensity distribution resulting from coherent scattering of a 800 nm 45 fs pulse with 10 - 60 GW peak power on the ensemble of water droplets with the atmospheric size distribution and the density 100 cm-3. The forward scattering on aerosol particles takes into account the phase of the scattered radiation. The transverse distribution of the laser field behind the aerosol layer is calculated as the result of the interference of light fields formed by each particular particle. In the numerical simulations the input radius of a Gaussian beam was a = 2.5 mm. The average size of an aerosol particle was 4 μ. The length of a propagation path was set to the half of the diffraction length: 0.5.ka2. As the result we have shown that in aerosol medium it is possible forming of several hot spots containing approximately 1 critical power for self-focusing.