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

Abstract

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.

Implementation of a dual-phase grating interferometer for multi-scale characterization of building materials by tunable dark-field imaging

“…In a DP-XGI, the polychromatic and cone-beam illumination nature of the imaging system implies that the effective energy, and therefore the correlation length, are energy spectrum and spatial dependant. Hence, the effective energy is measured as the average of each photon energy of the spectrum weighted by its quantum efficiency and the mean visibility spectrum ), as it is defined in a previous work 19 . The spectrum parameters were obtained with a Monte Carlo simulation reported by Dhaene 27 , and the mean visibility was obtained with the wave propagation cone illumination framework reported by Tang 20 .…”

“…The final performance of the DP-XGI compared to that predicted theoretically 19 depends on factors including source size, detector blurring, and effective shape of the produced grating, which may deviate given the very challenging design parameters 20 .…”

“…For that reason, the effective energy is both spatially dependent and spectrum dependent. For the calculation of the effective energy the source spectrum , the filters in the setup, the scintillator response, the grating’s materials, and the visibility per energy are required for its calculation as expressed in previous publications 19 . The values reported in the results were calculated with simulated values of the visibility spectrum 20 and the target spectrum 27 .…”

“…The interferometer module was designed to work in two different energy ranges and a Fresnel wave-front propagation simulation framework was carried out to select the optimal parameters 19 . For the low-energy (LER) configuration, the phase gratings are designed to produce a phase shift to a wavefront of 22.0 keV, while for the high-energy (HER) configuration, the phase gratings have a design energy of 40.8 keV and equal wavefront phase shift of .…”

“…In this work, the implementation of a lab-based DP-XGI setup aiming for a nanoscale characterization of building materials by tunable dark-field 2D imaging is presented. The imaging system has been optimized by a Fresnel-wave simulation framework 19 , 20 for a low (LER) and a high energy range (HER) to investigate feature sizes in a range from tens to hundreds of nanometers in various types of materials.…”