提出了一种激光光束整形自由曲面透镜的设计方法，这种方法可以对有一定发散角的激光光束进行整形。设计分为两个过程：1）设计初始结构，以准直激光光束作为输入光束，采用能量网格划分法，设计自由曲面整形透镜，将设计好的透镜作为下一步设计的初始结构；2）逆向反馈优化法，以带有一定发散角的光束作为输入光束，用上一步获得的透镜作为初始结构，采用逆向反馈优化的方法作进一步优化设计。应用这种方法，以束腰为10 mm，发散半角为2.5°的发散激光光束为例，将其整形为40 mm×40 mm的方形光束，辐射照度均匀度达到了90.4%。最后，对设计的透镜进行了加工误差分析和安装误差分析。分析结果表明：透镜表面面形误差在±5 μm范围内对目标平面辐射照度的均匀度几乎没有影响；透镜安装时，纵向位移误差dz对目标平面辐射照度的均匀度影响较小，横向误差dx、倾斜角误差dφ对辐射照度均匀度影响较大。

A design method of laser beam shaping freeform surface lens is proposed, which can be applied to shape the diverging laser beam. Freeform surface lens design is a two-step process. Firstly, an initial lens layout is designed by establishing the input-output energy mapping relationship. Then, the reverse feedback optimization method is used to optimize the initial freeform lens when the divergent beam is applied. By this method, a freeform lens is designed for shaping a laser beam with beam waist of 10 mm and a half divergence angle of 2.5°. The simulation results show that the freeform lens can transform a Gaussian beam into a 40 mm×40 mm top-hat beam with an irradiance uniformity of 90.4%. Finally, the machining error analysis and the assembly tolerance analysis of the freeform lens are performed. It is shown that the uniformity is almost unchanged while the process error varies from -5 μm to 5 μm. And the longitudinal deviation error dz has little influence on the irradiance uniformity, but the lateral deviation error dx and slant angle error dφ have a significant influence on the irradiance uniformity.