用高阶对比度研究光束的小尺度自聚焦

提出了高阶对比度这一新参数来描述光束的近场均匀性，并用之研究高功率激光装置中的小 尺度自聚焦现象.分析了高功率光束小尺度自聚焦发生的过程中填充因子、调制度、对比度 及高阶对比度随B积分值的变化，指出高阶对比度在光束出现自聚焦成丝前后有更显著 的变化，所以是描述小尺度自聚焦效应的理想参数.关键词：小尺度自聚焦三阶对比度四阶对比度功率谱密度相位噪声

Study of small-scale self-focusing in laser beams by high-order contrast

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.