建立了工作在一定入射角度范围内的多层衍射光学元件的复合带宽积分平均衍射效率的分析模型。基于衍射光学元件所具有的独特的消色差和消热差性质, 设计了一个含有双层衍射光学元件的工作在 3.7～4.8 .m和 7.7～9.5 .m红外双波段光学系统。光学系统的焦距为 100 mm, F#为 2, 采用像元数为 640×512、间距为 15 .m的制冷型探测器。该系统在空间频率 33 lp/mm时, 中、长波红外 MTF分别高于 0.52和 0.16, 最大 RMS半径小于 9.88 .m, 波前像差小于 0.0705., 最大离焦量小于焦深, 在－40℃～71℃范围内实现了无热化设计。系统中采用的双层衍射光学元件在红外双波段的带宽积分平均衍射效率高于 99.15%。入射到衍射面上的角度为 0°～10°, 该双层衍射光学元件在中波和长波波段的复合带宽积分平均衍射效率分别为 97.70%和 96.95%。

The analysis model of comprehensive bandwidth integrated average diffraction efficiency of multilayer diffractive optical elements (MLDOEs) operating within a range of incident angle was established. Based on the special characteristics of achromatism and athermalization of diffractive optical elements (DOEs), an infrared dual-band optical system with double-layer DOEs operating in the range of 3.7–4.8 .m and 7.7-9.5 .m wavebands was designed. The effective focal length of the optical system is 88 mm; F # is 2； the cooled focal plane array is 640.512, and the pixel pitch is 15 .m. MTF of the designed system were above 0.52 and 0.16 for the MWIR and LWIR, respectively, at a spatial frequency of 33 lp/mm, the maximal RMS radius was less than 9.88 .m, the wavefront error was smaller than 0.0705. and the maximal defocus was less than focus depth, and therefore, the designed optical system realized athermalization over the temperature range from .40℃ to 71℃. The bandwidth-integrated average diffraction efficiency of double-layer DOEs adopted by the proposed system for the two wavebands was more than 99.15%. The incident angle on the diffractive surface was within the range of 0°–10°, the overall bandwidth-integrated average diffraction efficiency of the double-layer DOEs were 97.70% and 96.95% for the MWIR and LWIR wavebands, respectively.