Abstract: According to the present demand for in-situ surface measurement of large aperture optical mirrors and the difficulties faced, a new method based on phase retrieval technology is proposed and an in-situ measurement system is established. Main factors that influence the accuracy of measurement system and the anti-vibration ability of system are analyzed and simulated. The results show that the measurement system has good anti-vibration ability, and the accuracy is close to that of standard spherical wave light source. The measurement software is developed on the basis of GS iterative algorithm and in-situ measurement of a spherical mirror of  500mm is carried out. The measurement results show good agreement with those of high-precision ZYGO interferometer in error distribution, PV value and RMS value, which confirms the feasibility and accuracy of the measurement method based on phase retrieval. This in-situ measurement system features simple optical path, high accuracy, good anti-vibration ability and simple operation, thus fully satisfying the demand for in-situ measurement of large aperture optical mirrors.

Key words: In-situ measurement, Large aperture mirror, Phase retrieval