Differential phase retrieval based on phase modulating for wavefront detection

Abstract

Wavefront aberration in optical imaging system reduces the image quality. The Gerchberg and Saxton algorithm is commonly applied to detect the wavefront from far-field intensities. Based on ‘alternating projection’, the algorithm is very sensitive to the initial phase guess, and can easily fall into a local optimal solution. In this paper, we propose an effective method based on phase modulation to obtain a favorable initial phase which ensures the GS iteration converge to the closely optimal solution. In the method, after the infocus image, add a suitable ‘phase mask’ to the incident beam and record the second far-field image. From the difference of the two images, a good approximation to the far-field phase can be solved directly, which reveals many crucial features of the exact far-field phase. With this value as the initial input, the GS iteration or other iterative Fourier algorithms would be able to achieve nearly global optimal phase retrieval.