Pendellösung fringes for X-ray spherical-wave diffraction in a perfect crystal

The results of experiments in which an anomalous form of the Pendellösung fringes has been discovered together with a classical one are presented. The general theory of X-ray spherical-wave diffraction has been constructed taking into account the change of phase relationships for radiation propagating in vacuum. An explanation of the observed experimental results and classification of possible manifestations of the Pendellösung effect are given. New data concerning the previously discovered phenomenon of focusing are presented.