Structured Filamentation of High-Power Femtosecond Laser Radiation Modulated by Amplitude Mesh Masks

The problem of controlling the parameters of the filamentation region of high-power femtosecond laser pulses for amplitude modulation of radiation by a metal mesh mask is theoretically considered. In this case, the initial laser beam is split into individual lower energy subbeams. This leads to a pronounced regularization of the spatial structure of the filaments, which is formed at the stage of radiation self-focusing due to diffraction interaction between subbeams in a nonlinear medium. Using numerical simulation, it is found that the total length of the filamentation region of femtosecond laser radiation in air is reduced when using modulation meshes. At the same time, the longitudinal continuity of laser plasma in such filaments can significantly increase. It is shown that the spatial parameters of filaments (coordinate of the beginning, length, and continuity) can be controlled over a wide range by changing mesh parameters (crosshair thickness and cell size), as well as the position of the mesh mask relative to the laser beam center. The results are important for predicting the propagation of high-power femtosecond laser radiation in a nonlinear medium, in particular, along atmospheric paths.