基于光学离焦量的致冷型长波变焦红外成像系统冷反射效应的分析与控制

Analysis and Control of Narcissus Effect of Long-Wavelength Cooling Infrared Imaging System Based on Optical Defocusing

衡量镜面冷反射大小的主要指标在于其对后向反射光线的在探测器靶面的聚焦程度,目前使用一阶参量yni进行量化,不足之处在于没有和具体的透镜参数和系统参数相联系,对于冷反射优化指导作用不大。定义了新的参量光学离焦量对反射光线的散焦进行量化,推导给出了其与镜面曲率半径、通光孔径、其后成像面位置、其前透镜组焦距和系统视场角等设计参数的关系式,分析总结了光学设计中降低冷反射的方法。利用光学离焦量对一个制冷型长波变焦红外光学系统进行了冷反射分析,并计算了各反射面的冷反射引入等效温差(NITD)。分析了NITD主要贡献面的冷反射成因,并进行了针对性的优化,优化后系统变焦部分的NITD减小了50%,而固定透镜组的冷反射下降了75%左右,结果表明光学离焦量对于制冷型红外系统的冷反射优化具有明显的指导作用。

At present the first-order parameter yni is used to quantify the focusing of retro-reflected rays on the detector plane,which causes narcissus effect.The shortage is that yni is not refrenced to the lens data and system data so it′s not useful to guide narcissus optimization.A new paramter——optical defocusing is defined to quantify the defocusing of retro-reflected rays,the relation between optical focusing and lens surface radius,aperture,position of intermediate image,focal length of lens before the surface and field of view is presented.Optical methods to minimize narcissus effect is summerized.The narcissus of a long-wavelength cooling infrared system is analysed with optical defocusing and the narcissus induced equivalent tempareture difference（NITD） is caculated.The major NITD contributing surfaces is optimised after which the NITD of zooming group drops by 50%,and that of fixed lens by 75%.The results demonstrate that optical defocusing can guide narcissus optimization effectively.