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Figure 2. Analyser-based phase contrast imaging schematic showing the geometrical optics construction for imaging a cylindrical object. The inset shows the analyser rocking curve for the Si(333) Bragg reflection as measured experimentally and calculated from theory (full width at half maximum 
5 x 10–6 radians). The theoretical curve incorporates the double-bounce Si(311) monochromator with the Si(333) analyser reflections and the known beam divergence for the beamline. 
L and H show the low and high angle points where the reflected intensity is at half of the peak intensity found at the Bragg angle B. Images are often acquired with the analyser tilted to either L or H since the intensity gradient with angle is a maximum, which provides large intensity changes for small angular deviations of X-rays.
