Impact of Spatial Filter Parameters on Output Beam Performance in High-Power Laser System: A Comprehensive Analysis

Spatial filters are critical components in high-power laser systems for improving laser performance, removing high-spatial-frequency components which experience high nonlinear gain, thereby ensuring safe operation under high fluence conditions. Based on free-space propagation models and nonlinear B-integral theory, this paper systematically investigates the relationship between the output beam modulation and the pinhole size of spatial filters under various operating conditions. First, the influence of wavefront perturbances on beam performance is illustrated, revealing that surface errors impose constraints on the allowable pinhole size. Furthermore, based on a high-power laser system of 4+2 multi-pass amplification prototype, the nonlinear gain and beam modulation along its propagation path are analyzed. This analysis yields insights into output beam quality under the influence of multiple factors. Finally, the study clarifies the evolution of output beam performance in relation to optical surface errors, the B-integral value, and spatial filter pinhole size. Based on these results, the ultimate output capability of the high-power laser system is discussed. This work provides a theoretical basis for optimizing the pinhole size of spatial filters and guarantees safe operation of high-power laser systems.