Influence of the transverse and longitudinal coherence in the dynamical theory of x-ray diffraction

We investigate dynamical diffraction phenomena of a quasi-monochromatic x-ray beam emitted by a small source at a large distance from the sample. Under certain conditions of coherence the diffraction intensity profile in a recording plane reproduces the angular profile of the rocking curve of the crystal. The coherence requirements are stronger for thicker crystals. This has been verified in experiments at the ESRF. In these experiments the effective crystal thickness was varied by rotating the crystal around an axis perpendicular to the reflecting planes.