Phase retrieval for hard x-ray in-line phase contrast imaging

Since hard x_ray in_line phase_contrast imaging is based on Fresnel diffraction of x_ray, we propose to make phase retrieval calculations between arbitrary plan es interrelated through the Fresnel domain. The calculation of the free space pr opagation is based on the angular spectrum approach, which can be used with Gerc hberg_Saxton algorithm for phase retrieval. We call this method the iterative an gular spectrum approach. The new method is tested on simulated images in the cas e of uniform illumination and is demonstrated to be efficient for phase retrieva l.