Comparison between experimental and theoretical rocking curves in extremely asymmetric Bragg cases of X-ray diffraction

Double-crystal rocking Curves from a highly perfect silicon crystal were taken in extremely asymmetric schemes, in which the glancing angles of the incident X-rays were very close to the critical angle of total external reflection. The experimental rocking curves were compared with theoretical calculations based both on an ordinary dynamical theory of diffraction and also on an extended dynamical theory, which uses a more exact solution of the fundamental equation of the dynamical theory and takes the effect of specular reflection into account. It is demonstrated from such a comparison that, in the case of extremely asymmetric diffraction, the ordinary treatment of the dynamical theory of diffraction is not valid; in contrast, the extended theory explains the rocking curve very well.