Simulations of phase imaging with polycapillary optics (Conference Presentation)

Abstract

X-ray phase imaging is known to enhance contrast, particularly for low atomic number materials, for which absorption contrast is low. However, it requires spatial coherence which is typically achieved with a small (10 to 50 µm) source, or a grating placed in front of the source to essentially break it into multiple small sources. In a previous experiment, polycapillary focusing optics were shown to improve coherence when employed to focus x rays from a large spot rotating anode to a smaller secondary source. Edge-enhancement to noise ratios up to a value of 6.5 were obtained, and sufficiently high quality data was obtained from a single image to allow for phase reconstruction using a phase attenuation duality approach. Alternatively, polycapillary optics might operate in place of a source grating to effectively divide the source into a very large number of small channels. In order to examine the potential use of polycapillary optics to enhance phase imaging, the phase and coherence properties of the optic were modeled by observing the fringe visibility in a simulated Young’s double slit experiment. The optic was modeled using simple ray tracing in a Monte Carlo simulation, with the phase advance associated with each photon path computed from the path length and phase changes upon each reflection through the polycapillary tube. Fringes, which disappeared with a large source, were maintained after the optics, implying that beam coherence was observed for both the collimating and focusing polycapillary optics.