Dynamics of femtosecond synthesized coronary profile laser beam filamentation in air

Abstract Multiple filamentation in air of high-power ultrashort laser radiation with a transverse intensity profile resembling a corona composed of several annularly distributed independent top-hat sub-beams is theoretically studied. Through the numerical solution of the time-averaged nonlinear Schrödinger equation, we study the spatio-angular dynamics of a near-infrared annular combined beam (CB) along the optical path by varying the number and power of the beamlets (corona-spikes). The evident advances in the use of CB in the multiple-filamentation region manipulation and for achieving long-range filamentation are theoretically revealed. In particular, by adjusting the number and aperture of the constituting sub-beams, it makes it possible to significantly delay the CB filamentation onset distance and increase the filamentation length in air. In addition, at the post-filamentation stage of femtosecond pulse propagation under certain conditions, the CBs exhibit significantly lower angular divergence of their most intense part (post-filamentation light channel) compared to the beams with regular unimodal intensity profiles (Gaussian or plateau-like) that provide enhancement of laser power delivered to the receiver over the atmospheric links.