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-r ay beam emitted by a small source at a large distance from the sample. Unde r certain conditions of coherence the diffraction intensity profile in a re cording plane reproduces the angular profile of the rocking curve of the cr ystal. The coherence requirements are stronger for thicker crystals. This h as been verified in experiments at the ESRF. In these experiments the effec tive crystal thickness was varied by rotating the crystal around an axis pe rpendicular to the reflecting planes.