Method for measuring the wavefront of a large-stroke VCM based on a simple optical system and an ordinary SHWFS

Wavefront measurement of a large-stroke variable curvature mirror (VCM) usually requires expensive equipment or a complex optical system. A method for measuring the wavefront of a large-stroke VCM based on a simple optical system and an ordinary Shark-Hartmann wavefront sensor (SHWFS) is proposed. The wavefront reflected from the VCM is limited to a small range by defocusing the light source (LS) adaptively according to the VCM wavefront, and the aberration influence of the relay optical system (ROS) between the VCM and SHWFS can be ignored. We demonstrate the effectiveness and superiority of our method. Compared with the traditional SHWFS method, the defocus measurement bias is approximately decreased from 40λ to 0.1λ when the VCM defocus is -160λ. The measurement accuracy can be further improved by reducing the LS defocus step size. The measuring range can be further enlarged by increasing the defocus range of the LS or decreasing the focal length of the collimating lens.