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Abstract
Phase retrieval is one of the most critical steps in coherent X-ray diffractive imaging (CDI), specifically in the Bragg scattering geometry, where crystalline distortions such as strain, tilt, or antiphase domain (APD) introduce strong fluctuations in the phase of the effective complex value electron density. The retrieved sample image corresponds to the convolution of the true effective electron density with the resolution function of the experiment. However, the currently best available image resolution (smallest pixel/voxel) with CDI is limited to the nanometer range, mostly due to experimental limitations such as limited X-ray photon flux or set-up instability, while crystalline distortion variations are often of smaller extent and corresponds to large phase shift. This convolution results in a degraded image, where the modulus of the effective electron density function, which is related to the sample electron density, cannot be reliably obtained. In this paper we show that the image distortion problem can be minimized if we employ a modulus homogenization (MH) constraint. We demonstrate how the convolution effect leads to an incorrectly retrieved modulus in regular CDI and show the efficiency of the MH constraint in obtaining a reliable APD reconstruction.