提出了基于复合型光栅组合的多色集束匀滑方案,可实现激光集束在靶面上平移和旋转两种运动方式的组合。建立了靶面散斑的横向扫动速度物理模型,并推导出激光束横向扫动速度的解析表达式,进而讨论了靶面横向扫动速度的变化规律。在此基础上,分析了不同复合型光栅组合对靶面辐照均匀性的影响,并对复合型光栅参数的选取进行了优化。结果表明,与传统的线性光栅色散匀滑方案相比,在使用复合型光栅时激光束靶面散斑的扫动速度和扫动方向更加复杂,因而其匀滑效果更佳。与典型的束匀滑方案进行对比,经过优化的基于复合型光栅组合的多色集束匀滑方案能够有效改善焦斑均匀性和抑制焦斑内部热斑比例。此外,采用功率谱密度曲线对激光束纵向强度分布特性进行初步分析,结果发现,基于复合型光栅组合的多色集束匀滑方案能有效降低激光束纵截面峰值强度。

A beam smoothing scheme for multi-color laser quad based on combination of hybrid gratings is proposed, which can achieve a combination of transverse and rotary moving of the speckles on target plane. The physical model of the transverse moving speed of the speckles on target plane is built up, and the analytical expression for the transverse moving speed of the speckles on target plane is also derived. Furthermore, the variation of the transverse moving speed of the speckles on target plane is discussed. On the basis, the influences of different combinations of hybrid gratings on irradiation uniformity on target plane are analyzed, and the parameters of hybrid gratings are optimized. Results indicate that, compared with the traditional scheme of smoothing by spectral dispersion based on linear gratings, the moving speed and direction of the speckles on target plane are more complicated based on hybrid gratings, resulting in the further improvement of the smoothing effect. Compared to the typical schemes of beam smoothing, the optimized scheme of beam smoothing for multi-color laser quad based on the combination of hybrid gratings can effectively improve the irradiation uniformity and reduce the ratio of hot spots. Additionally, the power spectral density is proposed and used to preliminarily analyze the longitudinal intensity distribution characteristics of laser quad, and it is found that the beam smoothing for multi-color laser quad based on the combination of hybrid gratings can effectively decrease longitudinal peak intensity of laser quad.