X-ray angle-resolved computed tomography using an asymmetric analyzer crystal

Because X-ray angle-resolved computed tomography is sensitive to the X-ray phase gradients produced by a sample, it has much higher sensitivity than the conventional techniques based on the absorption contrast. To improve this technique, we introduced an asymmetrically cut crystal for the analyzer, which functions as either a magnifier or demagnifier. For image magnification at a wavelength of 0.0766 nm, we utilized an asymmetric Si(220) crystal (θB=11.5deg), the diffraction plane of which was inclined by 8deg from the crystal surface. The magnification ratio, m, was 5.47 and improvement of spatial resolution was successfully observed. In the image demagnification experiment, another asymmetric Si(220) crystal (m=0.49) was used, and cross-sectional images were successfully reconstructed for a sample larger than the viewing field of the X-ray charge coupled device (CCD) image sensor. The asymmetric analyzer opens up new ways, for example, to improve the spatial resolution of pixel array detectors (PADs) for high-sensitivity and high-resolution phase-contrast X-ray imaging. (author)