Optimization of the visibility of a tunable dual-phase x-ray grating interferometer

Dual-phase x-ray grating interferometry (DP-XGI) is a recently developed imaging technique that can retrieve structural information in the sub-micro scale over areas in the millimeter range. This is performed by use of the scattering signal, which is sensitive to structures that lie below the intrinsic spatial resolution of the imaging system. A quantitative understanding of the microstructure is possible when the scattering signal is retrieved within a range of auto-correlation lengths of the features of interest. High visibility of fringes in this length range is desirable, but no straightforward framework exists for choosing design parameters of the imaging system for such optimization. The purpose of this work is to present an optimization protocol for DP-XGI based on a Fresnel propagation simulation framework which evaluates different parameters of the optical system, utilizing the mean visibility of the fringes at the detector plane as a figure of merit to optimize the DP-XGI for a conventional lab x-ray source. The performance of the numerical simulation with realistic component parameters is validated with the experimental results obtained at a lab-based setup. The results of the validation confirm the robustness of the model for the evaluation of the different components of the interferometer and its optimization at low and high energies.