Iterative phase retrieval imaging based on alternating wavefront curvature

The key to phase retrieval imaging is the recording of the same information on multiple speckle de-correlated patterns. Various techniques have been developed based on this principle such as alternating recording distance, alternating wavelength and alternating illumination pattern. Here we discuss a novel phase retrieval technique, where diffraction patterns with varying illumination-source object distance are recorded. This has the same effect as changing the object sensor distance, with the advantage of not having to sacrifice resolution. Moreover, a mismatch of information as caused by dispersion effects when employing different wavelengths is avoided. These claims are confirmed via an experiment on a USAF test target and the usefulness of its quantitative phase imaging capability is demonstrated for tissue discrimination.