Fig. 1. Layout of coaxial four-mirror optical system

Fig. 2. Layout of optical aperture

Fig. 3. Structural diagram of optical system

Fig. 4. Monolithic structure diagram of primary mirror and tertiary mirror

Fig. 5. Spot diagrams of optical system with different fields. (a) 0° field; (b) 1° field; (c) -1° field; (d) 1.5° field; (e) -1.5° field

Fig. 6. MTF of optical system

Fig. 7. Wavefront aberration RMS of optical system

Fig. 8. Field curvature and distortion of optical system. (a) Field curvature; (b) distortion

Fig. 9. Optical and mechanical structures of coaxial four-mirror optical system based on multi-surface integration. (a) Side view;(b) section side view

Fig. 10. MTF at different temperatures. (a) -30 ℃; (b) -5 ℃; (c) 20 ℃; (d) 45 ℃; (e) 70 ℃

Fig. 11. Layout of detector position

Fig. 12. Incoherent irradiance at different positions. (a) Detector 1; (b) detector 2; (c) image detector

Fig. 13. Ray path of 0° field

Fig. 14. Ray paths of 1.5° field. (a) Ray path; (b) stray light 1; (c) stray light 2

Fig. 15. Typical stray light paths of 1.5°-10° field. (a) Two reflections; (b) irregular reflection; (c) mechanical reflection

Fig. 16. Typical stray light paths of 10°-50° field. (a) Mechanical reflection; (b) irregular reflection; (c) direct radiation

Fig. 17. Suppression of stray light. (a) Superimposed optical path of 0° and 5° field; (b) irradiance of 0° field; (c) superimposed irradiance of 0° and 5° field