为解决目前激光测距接收光学系统存在的难点，即系统在具有充足进光量的同时又要保证其低制造成本和轻小型化，基于拉格朗日不变量理论分析设计了一种大相对孔径接收光学系统。系统采用6片式伽利略型标准球面镜，使用光敏面直径为0.5 mm的雪崩光电二极管（APD）探测回波光信号，优化后的系统入瞳直径为50 mm，相对孔径为1∶0.9，系统总长为114.9 mm，拉格朗日不变量为125 mrad·mm，获得了较为充足的进光量的同时满足低成本小型化要求。为降低杂散光的影响，进一步设计了遮光罩及镜筒栅栏结构。杂散光模拟追迹结果表明，系统在20°~85°离轴角视场外的杂散光抑制可以达到激光测距系统要求。在接收光学系统拉格朗日不变量为125 mrad·mm的前提下，激光测距系统的测距量程在加入光学系统后综合提升了21倍，表明该接收光学系统具有较大应用价值。

To solve existing difficulties in the current laser ranging receiving optical system, that is, the system has sufficient light input while ensuring its low manufacturing cost and light miniaturization, a large relative aperture receiving optical system is analyzed and designed based on the Lagrange invariant theory. The proposed system uses a six-piece Galilean standard spherical mirror, and an avalanche photodiode (APD) with a photosensitive surface diameter of 0.5 mm, to detect an echo light signal. The optimized system consists of an entrance pupil diameter of 50 mm, a relative aperture of 1∶0.9, a total system length of 114.9 mm, and a Lagrange invariant of 125 mrad·mm, which not only obtains sufficient light input, but also addresses low-cost miniaturization requirements. To reduce the stray light influence, the lens hood and barrel fence structure are further designed. Stray light simulation tracking results indicate that the stray light suppression outside the 20°‒85° off axis angle field of view meets the laser ranging system requirements. Under the premise of receiving an optical system with a Lagrange invariant of 125 mrad·mm, the ranging range comprehensively increased by 21 times after adding the optical system. This confirms that the receiving optical system has significant application value.