We present a general analytic approach to spatially resolve the nano-scale
lattice distortion field of strained and defected compact crystals with Bragg
coherent x-ray diffraction imaging (BCDI). Our approach relies on fitting a
differentiable forward model simultaneously to multiple BCDI datasets
corresponding to independent Bragg reflections from the same single crystal. It
is designed to be faithful to heterogeneities that potentially manifest as
phase discontinuities in the coherently diffracted wave, such as lattice
dislocations in an imperfect crystal. We retain fidelity to such small features
in the reconstruction process through a Fourier transform -based resampling
algorithm designed to largely avoid the point spread tendencies of commonly
employed interpolation methods. The reconstruction model defined in this manner
brings BCDI reconstruction into the scope of explicit optimization driven by
automatic differentiation. With results from simulations and experimental
diffraction data, we demonstrate significant improvement in the final image
quality compared to conventional phase retrieval, enabled by explicitly
coupling multiple BCDI datasets into the reconstruction loss function.Comment: 30 pages, 23 figure