The control of fast nonlinear growth in picosecond laser

The high-power picosecond laser systems have been used in many fields, such as materials dynamics research, cancer treatment, and high spatial and temporal resolution backlight radiography[1] . Compared to nanosecond laser, picosecond laser with higher peak intensity can generate more serious fast nonlinear growth, which leads to the small-scale autofocusing (SSSF) effect and the beam splitting into filament, affecting the safe operation of the laser system and limiting its output capability. How to effectively suppress the fast nonlinear growth and improve the near-field quality of the output beam in picosecond laser systems has become a hot topic of interest. In recent years, a band-stop filtering technology based on volume Bragg gratings (VBGs) has been proposed, which can effectively filter out the specific medium-high frequencies (MHFs) of the beam and suppress the SSSF effect. In this paper, a filter based on the composition of two VBGs is designed to take advantage of the excellent angular selectivity of the VBG. The incident angle of the incident beam is matched with the first diffraction zero point of VBGs to constitute a band-stop angular filter (BSF). Combined with the picosecond laser amplification system, the ability of BSF to suppress the fast nonlinear growth generated is investigated. The near-field distribution of the beam through is numerically simulated. This method proposed in this paper effectively suppresses the SSSF effect of the beam in high-power laser systems and provides a new technical approach for picosecond laser amplification.