Interpretation of dark-field contrast and particle-size selectivity in grating interferometers

作者：Susanna K. Lynch, Vinay Pai, Julie A. Auxier, Ashley Stein-Merlob, Eric E. Bennett, Camille K. Kemble, Xianghui Xiao, Wah-Keat Lee, Nicole Y. Morgan, Han Wen · 发表于：Applied Optics · 年份：2011 · DOI：10.1364/ao.50.004310 · 被引用次数：198 · 研究领域：Advanced X-ray Imaging Techniques、X-ray Spectroscopy and Fluorescence Analysis、Crystallography and Radiation Phenomena

In grating-based x-ray phase sensitive imaging, dark-field contrast refers to the extinction of the interference fringes due to small-angle scattering. For configurations where the sample is placed before the beamsplitter grating, the dark-field contrast has been quantified with theoretical wave propagation models. Yet when the grating is placed before the sample, the dark-field contrast has only been modeled in the geometric optics regime. Here we attempt to quantify the dark-field effect in the grating-before-sample geometry with first-principle wave calculations and understand the associated particle-size selectivity. We obtain an expression for the dark-field effect in terms of the sample material's complex refractive index, which can be verified experimentally without fitting parameters. A dark-field computed tomography experiment shows that the particle-size selectivity can be used to differentiate materials of identical x-ray absorption.