Study of small-scale self-focusing in laser beams by high-order contrast
用高阶对比度研究光束的小尺度自聚焦

In this paper, high_order contrast is brought forward for studying small_scale s elf_focusing phenomenon in high_power solid state laser drivers. Based on the p roperties of semi_invariant, we obtain the analytic expressions of high_order co ntrast of near field of beams. Finally, we study the propagation of plane waves w ith PSD phase noise and obtain the evolution of fill factor, modulation, contras t, third_order contrast and fourth_order contrast with B-integral value. Compa ring t he results of numerical simulation, we find that third_order contrast and fourth _order contrast are good parameters for characterizing the small_scale self_focu sing phenomenon.