在大地测量领域中，经常会遇到需要产生360°环形准直光束的情况，目前采用的方案是将半导体激光器光束准直，准直后激光束垂直入射到45°圆锥面，经圆锥面反射后形成环绕圆锥面的360°环形出射光束。为了解决当前方案结构复杂、装调不便等问题，研究设计了一种自由曲面反光镜，使得整个光学系统仅由半导体激光器和反光镜组成。先将光源当成理想点光源，通过微分几何分析得到自由曲面离散点坐标，继而拟合成自由曲面面型，最后利用软件根据实际光源尺寸大小进行优化设计。仿真结果表明，在半导体激光器发散角为20°、发光面半径为50 mm、焦距为30 mm 的情况下，在10 m 位置能得到亮度均匀、谱线宽度仅为30 mm 的准直光束。

In the field of geodesy, it is common that engineers need to produce 360° circular collimated beam. Now, the scheme is collimating beam from semiconductor laser firstly. Then, projecting the collimated beam to a cone with a inclination of 45° and 360° circular collimated beam comes out. To solve existing problems such as complex structure, inconvenient installation and so on, a design of free-form reflector is proposed to make the whole optical system consist of semiconductor laser and reflector only. The first step is calculating discrete coordinates of freeform by establishing a differential equation in the case of assuming the source to a point source. Then fitting to a freeform surface with the discrete coordinates as above. At last, carrying out a optimization design in the software according to the actual size of source. Then the free-form surface will be obtained with the discrete coordinates as above. Finally, lighttools is used to optimize the optical system according to actual size of light source. The simulation reveals that semiconductor laser with 20° divergence, 50 mm radiusand 30 mm focus can obtain uniform beam of 30 mm width 10 m away.