Photon-counting shearing interferometer

We have designed and built a photon-counting shearing interferometer which is capable of performing the wavefront gradient measurement of photon levels in real-time. This paper describes its principle and configuration, and analyzes its capability of wavefront sensing. The shearing interferometer has been used in the adaptive optics image compensation system for astronomical observation and successfully tested on the 1.2 m telescope of Yunnan Observatory in China from 1990 to 1992.