Preliminary analysis and experiment of thermal influence on a large aperture mirror

Thermal distortion of the optical elements can greatly reduce the high resolution of the space-borne camera. The general thermal effect on mirror is analyzed and the optical aberration of the optical surface resulting from 3 kinds of thermal gradient is discussed. The thermal distortion simulating experiment of a large aperture flat mirror is designed and the optical aberration is tested on 18'' ZYGO with the different axial thermal disturb. The testing results conclude that the small thermal gradient can greatly affect the wave-front, the aberration of this large aperture flat mirror can be used to simulate the thermal distortion on space, and MTF is also reduced greatly when this large aperture flat mirror is used in the real space-borne camera under the same thermal environment. In order to correct the thermal distortion and keep the high resolution, the 37-units adaptive optics correction close loop experiment is designed and installed in the above camera. The correction results show that MTF of the testing camera will not reduced greatly under the large thermal distortion. So employing adaptive optics on a high resolution space camera is the necessary and the valid method to correct the thermal distortion.