The infrared multi-band optical system can track the band information stretching from mid-wave infrared to long-wave infrared ,which can greatly improve the information ac-quisition capability .A infrared multi-band optical system composed of 4 spherical lenses was designed based on the compact principle .It could image clearly at 4 .4μm~8 .8μm continuous-ly ,the F# was 2 .68 which strictly matched with the cold light bar so that the cold light bar effect reached 100% .T he system used the passive athermalization method to get rid of tem-perature compensation problem and finally realized athermalization for continuous bands through selection of lens materials and formula derivation .The tube was made of titanium al-loy ,the lens was made of ZnSe ,Germanium and ZnS materials .The modulation transfer funtion (MTF) at 40 ℃ to 60 ℃ was given ,as well as the distortion over every wavebands .The result show s that the design of the system structure is relatively simple ,w hich satisfies the require-ments of a standard infrared thermal imager .%宽谱段红外光学系统可以获取宽谱段的图像信息并增大目标信息获取程度。从红外光学系统的简洁性出发，对红外光学系统进行设计，系统仅由4片球面透镜组成，实现了4．4μm～8．8μm波段清晰成像， F＃为2．68，达到了100％的冷光阑效应。采用被动消热差方式通过合理选择镜片材料及公式推导最终实现了各个波段内的消热差，镜筒材料为钛合金，透镜采用硒化锌（ZnSe），锗（Ge）及硫化锌（ZnS）材料，给出20 lp/mm处系统在各个波段在-40℃～60℃的工作温度下的调制传递函数（MTF），以及各个波段下的光学系统畸变值。实验结果表明：设计的宽谱段红外光学系统结构简单，满足设计要求。
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