针对像元尺寸为50 μm×50 μm的长波红外32×32元制冷型凝视焦平面阵列探测器的需要,设计了一种工作波长位于15~35 μm的透射式长波红外显微成像光学系统。该系统采用一次性成像方式,且主要由系列透镜构成,其中冷光阑置于光路的出瞳位置。通过对称双胶合透镜组合来校正像差,在-20~40 ℃温度范围采用光学被动补偿技术实现消热像差。仿真结果表明,当所设计的光学系统的中心波长、焦距、数值孔径、有效放大倍率和空间分辨率分别为27 μm,14 mm,0.25,10和0.1 mm时,在10 lp·mm -1特征频率处调制传递函数(MTF)值达到0.369,系统包围圆能量集中度超过80%,能够得到清晰可辨的物像,满足对冷光学系统短结构、高分辨率的应用需求。

In this study, a transmission type long-wavelength infrared microscopic imaging optical system operating in wavelengths of 15-35 μm is designed to meet the demand for cooled staring focal plane array detector containing long-wavelength infrared 32×32 pixel elements and exhibiting an elemental size of 50 μm×50 μm. The designed system adopts disposable imaging and comprises a series of lenses. A cold diaphragm is positioned at exit pupil of the optical path. Symmetrical double gluing lens combination is introduced into the system to correct the aberration. Further, an optical passive compensation technique is employed to realize anti-thermal aberration at temperatures of -20 ℃ to 40 ℃. The simulation results show that the designed system exhibits a modulation transfer function (MTF) value of 0.369 and an encircled energy concentration of >80% at a characteristic frequency of 10 lp·mm ^-1 when its center wavelength, focal length, numerical aperture, effective magnification, and spatial resolution are 27 μm, 14 mm, 0.25, 10, and 0.1 mm, respectively. Furthermore, a clear distinguishable image can be obtained using the designed system. The designed system satisfies the requirement of short structure and high resolution of cold optical system.