Contrast in X-ray section topographs of perfect silicon crystals using the Laue-Laue three-beam case of diffraction

Section topographs taken in three-beam diffraction geometry and in the neighbourhood of this geometric position are presented. The experiments were performed using polychromatic and monochromatic X-ray radiation. The interference of the two diffracted waves produces new contrast phenomena compared to the two-beam case. The contrast changes are discussed on the basis of the Bethe approximation by means of the effective structure factor and with regard to the dispersion surface of the three-beam case.