高功率激光系统空间滤波的离焦容限分析

在惯性约束聚变高功率激光装置中,严重的低频波前畸变会引起空间滤波的小孔截断,降低光束质量。采用相位调制的离焦波前来分析不同程度的离焦对空间滤波过孔和输出光束质量的影响,得到了空间滤波器对波前离焦的容限。在这种模型下的计算结果表明,球面相位因子入射光聚焦光斑焦点位置的偏移距离与其曲率半径成反比,光束质量随着输入光束曲率半径的绝对值减小而降低。对于等焦距11.8m、小孔半径角200μrad的空间滤波器,临界频率处畸变波前的球面相位因子曲率半径绝对值不能小于3.5km。曲率半径为3km时,相位调制的空间频率小于1.57mm-1时光束质量会急剧下降。

Analysis of the Defocusing Tolerance of Spatial Filtering in High Power Laser Systems

In the inertial confinement fusion high power laser systems, the severe low frequency wavefront distortion will result in laser beam cutoff, and reduce laser beam quality due to the pinhole of the spatial filter. Based on the spherical wave factor with phase ripples, the defocusing tolerance of spatial filtering has been studied in detail. In this model, the calculation result shows that the shift distance of the actual frequency-plane in the spatial filter is in inverse proportion to the curvature radius. In addition, the beam quality will reduce with the curvature radius decreasing. For a specified spatial filter with parfocal length of 11.8 m and filtering pinhole radius of 200 μrad, the curvature radius absolute value of the spherical wave factor should not be small than 3.5 km for the critical frequency. When the curvature radius grows to 3 km, the beam quality will deteriorate rapidly as the spatial frequency of phase ripples become smaller than 1.57 mm-1.