  We introduce a new X-ray imaging technique to facilitate propagation-based
phase contrast of large, centimeter-sized samples. The diffracted X-ray
wavefield behind the sample is demagnified by asymmetric Bragg crystal optics,
thereby virtually increasing the propagation distance and thus enhancing the
image contrast. We demonstrate the significant increase in image contrast
compared to conventional phase contrast imaging at the same short physical
propagation distance. Additionally, the Bragg demagnifier enables the reduction
of image blur caused by the finite X-ray source size. In combination with a
subsequent Bragg magnifier, the method will allow for an even higher dose
efficiency, rendering this technique a potential candidate for, e.g., low-dose
(bio)medical diagnostics.
