基于球面反射温阑的红外探测器变f数设计

制冷型红外探测器f数由冷阑尺寸和位置决定,在冷阑附近加温阑可以改变探测器f数,但是会引入大量杂散辐射.为解决这一问题,提出一种基于球面反射温阑的红外探测器变f数设计方法.建立了温阑红外辐射模型,分析普通平面温阑引入的杂散辐射及其对探测器性能的影响.在此基础上提出球面反射温阑的设计方法,通过改变表面形状和发射特性,降低温阑引入的杂散辐射,以保证探测器变f数后的性能.为验证本文方法,设计球面反射温阑和普通平面温阑改变某制冷型探测器f数,在高低温试验箱内进行辐射定标实验测量两种温阑引入的杂散辐射,比较二者对探测器的影响.分析和实验结果表明,球面反射温阑引入的杂散辐射远小于普通平面温阑,引入的噪声等效温差也较小,能够更好地保证红外系统的成像性能.

Design of varying f/number of cooled infrared detectors based on spherical reflecting warm shield

As is well known, the f/number of a cooled infrared detector is determined by the aperture and position of the internal cold shield. Moreover, the f/number can be changed by inserting a warm shield in front of the detector. In order to reduce the stray radiation introduced by an ordinary planar warm shield, we propose a method of varying f/number of the infrared detector based on a well-designed spherical reflecting warm shield in this paper. First, an infrared radiation model is established in order to analyze the influence of the stray radiation introduced by the ordinary planar warm shield. Then the design principle of the spherical reflecting warm shield is put forward. By changing the surface shape and emission characteristics, the stray radiation introduced by the ordinary planar warm shield can be obviously reduced. Hence it is beneficial to maintain the performance of the detector effectively while the f/number is changed. To validate the proposed method, a spherical reflecting warm shield and an ordinary planar warm shield are designed to vary the f/number of a cooled infrared detector respectively. To compare the influences of the two warm shields on the cooled infrared detector, radiometric calibration experiments are conducted in a high-low-temperature test chamber. The analyses and experimental results show that the stray radiation of spherical reflecting warm shield is far less than that of the ordinary planar warm shield. Moreover, the noise equivalent temperature difference introduced by the designed spherical reflecting warm shield is lower. Therefore it is indeed better than an ordinary planar warm shield in ensuring the performance of an infrared imaging system.