Peculiarities of the diffraction contrast in plane-wave X-ray topographs of weakly deformed crystals in the bragg geometry

The regularities of the topographic contrast formation in weakly deformed nonabsorbing crystals in the Bragg geometry for the diffraction of a plane X-ray wave have been investigated by the method of Riemann functions. It is shown that in this case the extinction contrast has an interference character, alternates, and is proportional to the strain gradient rather than to the squared strain (like in the case of strong lattice distortions). The data of the analysis are compared with the results of a model numerical experiment. The possibility of implementing an X-ray-acoustic resonance in the Bragg geometry is shown.