相位恢复测量长焦距镜面

针对长焦距光学镜面检测中测量光路长，振动干扰较大，不容易用干涉仪进行面形检测的难题，提出了一种基于相位恢复技术的测量方法.该方法用相干点光源照射被测镜，采集一系列焦点附近的衍射光强图像，然后运用相位恢复算法得到镜面面形误差分布.利用衍射光学理论建立了测量模型，并用基于Gerchberg-Saxton算法的迭代算法求解模型.然后仿真验证了光场传播模型的可靠性和测量算法的有效性，并用该方法测量了一块曲率半径8 700 mm，口径145 mm的球面镜.通过对光强图像位置进行优化，并选择适当离焦位置的图像，最终恢复出了镜面面形.相位恢复测量的结果与动态干涉仪测量结果基本一致，并且测量装置简单，对环境要求低.

Surface Measurement for Long Focal Length Mirror with Phase Retrieval*

In order to solve the difficulties in testing surface of long focal length mirror using interferometer,a novel optical metrology using phase retrieval is developed. In this method, tested mirrors is illuminated by a coherent point light source, a series of diffraction intensity patterns near focus are collected, then phase retrieval algorithm reconstructs the surface error of tested mirror. Compared with interferometer, it simplifies the metrology setup and requires no special environment. Mathematic model of phase retrieval measurement is found according to diffraction theory, and is solved by iterative algorithm which derives from Gerchberg-Saxton algorithm. Validity of this method is tested by simulations and an experiment. A spherical mirror with curvature radius of 8 700 mm and diameter of 145 mm is tested using phase retrieval. The position of intensity patterns are corrected and appropriate patterns are chosen to be computed. The reconstructed result is correlated well with that tested by simultaneous phase-measurement interferometer.