研究了制冷型红外离轴三反光学系统成像原理和优化设计方法。给出了一个应用自由曲面的制冷型离轴三反射镜光学系统的设计。系统采用两个自由曲面反射镜和一个偶次非球面反射镜组成二次成像的结构形式, 将制冷型红外探测器的冷光阑作为系统的孔径光阑, 得到100%的冷光阑效率。第二和第三反射镜将孔径光阑成像在第一反射镜的位置, 显著减小第一反射镜的口径。通过调整每个反射镜的偏心与倾斜, 实现系统的无遮拦, 使用自由曲面增大视场、校正像差、保证系统的成像质量。该系统的工作波段为3~5 μm, 焦距为450 mm, F数为2, 视场为3.662°×2.931°, 各视场的调制传递函数在环境温度为-40~60 ℃的范围内均高于0.5, 实现系统的无热化, 并且结构紧凑。

The principle and optical design method of cooled off-axis reflective optical systems were analyzed. An optical system design of a cooled off-axis three-mirror optical systems based on freeform surfaces was presented. This cooled off-axis three-mirror optical system was composed of two freeform surfaces and one even aspherical surface, which was a re-imaging structure with cold stop as the optical stop that could ensure 100% cold shield efficiency in the optical system. The optical stop could be imaged at the position of the first mirror by the second mirror and third mirror, which could reduce the size of the first mirror obviously. With the three mirrors optimized after optimization design including tilted and decentered methods, the system unobscured could be achieved and the freeform surfaces could be used to enlarge the field of view, correct image aberrations and improve the total image quality of the system. This system is with 450 mm focal length, 3-5 μm working waveband, 2 F-number, 3.662°×2.931° field-of-view. In addition, the modulation transfer function(MTF) of the system is above 0.5 all over the field of view with the working temperature range from -40 ℃ to 60 ℃. The result shows that the system has compact structure and athermalization achievement.