Fig. 1. Lightpath of optical system off-axis point imaging

Fig. 2. Optical analysis model of infrared detector

Fig. 3. Height and uniformity distribution of cold shield. (a) Maximum response and temperature gradient curves in the focal plane of cold shield; (b) uniformity distribution in the focal plane

Fig. 4. Four designed structures for cold shield. (a) Tower type; (b) accordion type; (c) straight cylinder type; (d) inverted cone type

Fig. 5. PST curves of four cold shield structures at different F numbers. (a) F1.2; (b) F2; (c) F3; (d) F4; (e) F5.5

Fig. 6. Sidewall venting structure and radiation distribution. (a) Sidewall venting; (b) path of stray radiation; (c) radiation of sidewall venting

Fig. 7. Improved venting structures and radiation distribution. (a) Top venting; (b) countersunk venting; (c) step venting; (d) top venting radiation; (e) countersunk venting radiation; (f) step venting radiation