Multiple-beam Bragg diffraction in backscattering: The four-beam case

Abstract

We present results of experimental and theoretical studies of four-beam x-ray Bragg diffraction in the important special case, when one of the Bragg reflections is in backscattering. The Bragg reflections accompanying the backreflection are excited always in pairs. As a result, the minimum number of diffracted waves is four (including the forward diffracted wave). Therefore, the four-beam case under study is the simplest multiple-beam Bragg diffraction case with one reflection in backscattering. The angular and the energy spectra of the reflectivity are investigated for all diffracted waves simultaneously. The measured spectra are in good agreement with the dynamical theory calculations. Diffraction was studied in a sapphire $(\ensuremath{\alpha}{\text{\ensuremath{-}}\mathrm{Al}}_{2}{\mathrm{O}}_{3})$ single crystal having the rhombohedral lattice. This is the first example of using a noncubic crystal in investigations of multiple-beam Bragg diffraction.