X-Ray Topography of Perfect Crystals using the Laue-Laue Three-Beam Case of Diffraction

A new kind of experiments is possible using very good collimated X-rays with a divergence of the incident beam smaller than the diffraction curve (rocking curve) of perfect crystals. Some examples are shown for the three-beam case of diffraction where both reflections are in Lauegeometry. The modification of the structure factor of a two-beam case reflection in the neighbourhood of a three-beam case causes a modification in the intensity distribution inside the Borrmann fan, which can be seen in section topographs. The energy flow in the three-beam case can be made visible in experiments with a very narrow incident beam with a 30 × 30 μm² cross-section.