The dynamical diffraction of X-ray spherical waves in two perfect crystals

The general theory of X-ray spherical-wave diffraction in two, either identical or different in nature, spatially separated perfect crystals is developed. The theory takes into account the phase shift of the waves both inside the crystals and in vacuum before, between and after the crystals. The nonmonochromaticity of radiation, the source dimension and the placing of a slit before the first crystal are considered. The results of theoretical calculation and an experimental study of the interference fringes and focusing the radiation are presented. A good agreement between the experimental and theoretical data is obtained for values of the experimental parameters that affect focusing.