分析了温度变化对红外光学系统结构参数的影响，给出了红外光学系统消热差设计应满足的条件，讨论了衍射光学元件的温度特性，并将其引入到红外光学系统的消热差设计中。利用ZEMAX软件，设计了一套由锗和硫化锌组合的三片式折衍混合长波红外光学系统，其工作波段为8~12 μm，视场为10.2°，焦距为45 mm，F/#为1.5，总长为70 mm。设计结果表明，该镜头在-40~60 ℃温度范围内成像质量接近衍射极限，系统全视场调制传递函数在特征频率20 lp/mm处高于0.6， 87%的能量集中在探测器的一个像元内，实现了消热差设计。该系统具有结构紧凑、体积小、质量轻等优点，适用于**或空间红外系统。

The influences of infrared optical system structure parameters, which caused by temperature change, was analyzed. And the condition of infrared optical system athermal design was provided. Then, the temperature characteristic of diffractive optical element was discussed, and it was introduced into infrared optical system athermal design. A long-wave infrared optical system with hybrid refractive/ diffractive was designed by ZEMAX. The system was composed of three lenses, which used only two materials of Ge and ZnS, including five spherical surfaces and a diffractive surface. Its operating band was 8 to 12 μm, the filed of vision angle was 10.2°, the focal length was 45 mm, the F/number was 1.5 and the total length was 70 mm.The design result shows that the image quality of the system can approach the diffraction limit at the working temperature of -40 ℃ to 60 ℃. The modulation transfer function(MTF) is greater than 0.6 in the full filed of vision when the Nyquist frequency of detector is 20 lp/mm, and 87% of the energy is focused in single pixel. The imaging quality of the system is good, and athermal design is realized. The optical system has many advantages, such as compact structure, small volume, light weight and so on. It can be applied to martial or special infrared system.