Pendellosung interference in the Bragg reflexion of X-rays from a crystal surface

Abstract

Abstract The dynamical theory of X-ray diffraction by perfect crystals applied to Bragg-case reflexion of a spatially narrow beam of coherent spherical waves at a crystal surface predicts that the spatial intensity distribution of the reflected beam contains oscillations due to Pendellosung interference, but with amplitudes very rapidly decaying in comparison with those occurring in the transmission (Laue) case. Computed intensity profiles for the Bragg case show that when unpolarized X-radiation is used superimposition of fringe patterns due to the perpendicular and parallel polarization modes will destroy fringe visibility unless the Bragg angle, 0B, is quite small or 20B is close to 90°; doubt is thus cast on Uragami’s (1969) claim to have observed fringes in an experiment with 20B = 43°.