中文摘要：

设计了工作于8～12 μm波段的折/衍混合双位置两档变焦光学系统.该系统变焦过程中相对孔径保持不变,F/#为1.7,系统变倍比为3.75∶1.大视场角为19.2°,有效焦距33 mm,用于在大范围内搜索目标;小视场角为5.1°,有效焦距125 mm,用于对目标进行具体分析.系统采用锗和硒化锌两种材料,为四片镜结构,仅通过两片透镜的轴向移动便可完成两个视场的切换.系统中引入二元面和高次非球面,使系统结构简化,并极大地提高了成像质量.该系统适用于像元尺寸20μm的非致冷式面阵探测器,可广泛应用于军事扫描成像和红外前视系统中.

英文摘要：

An infrared diffractive/refractive two-position step-zoom optical system in 8~12 μm was designed.The relative aperture was invariant during the zooming process.The F number of the system was 1.7,and the zoom ratio was 3.75∶1.In the wide-angle mode, the field-of-view was 19.2°,and the effective focal length was 33 mm.In the narrow-angle mode,the field-of-view was 5.1°,and the effective focal length was 125 mm.The wide field-of-view was used for searching for possible targets of interest,and the narrow field-of-view was used for final target recognition and identification.The system which has only four lenses contains three germanium lenses and one zinc selenide lens.To achieve a switchable dual field-of-view system,an optical configuration based on the axial motion of two lens along the optical axis was used.The binary surface and high order aspheric surface were used to simplify the configuration,lighten the weight and improve the image quality markedly.The system was applicable to the uncooled staring focal plane array（FPA） detector which has a pixel pitch of 20 μm.The system can be widely used in the martial scanning infrared imaging system and FLIRs.