NSLS-II Seminar

Abstract

Multiple-wave x-ray diffraction takes place when more than one set of atomic planes is simultaneously brought into position to diffract an incident beam. As a result of the scattering of x-rays from periodic two- or three-dimensional structures, the multiple-wave diffraction reflects structural crystal information that cannot be obtained from single two-wave diffraction.
However, due to the comparably large number of waves involved in the multiple-wave diffraction process, generally, the correspondent wavefields and diffracted intensities cannot be resolved analytically. For this reason, we have developed several approaches for numerical solution of the multiple-wave dynamical x-ray diffraction equations for bulk crystals and crystalline multilayers in a plane-wave approximation of the incident beam. We also proposed several approximations, including the iterative Born and resonance perturbation Bethe approximations, for the explanation of the fundamental behavior of three-wave x-ray diffraction. Among such behavior we have theoretically predicted and experimentally studied some new phenomena of a multiple-wave interaction of x-rays with matter: the indirect excitation of polarization-forbidden x-ray reflections, the polarization suppression of the detour-excited waves, the anomalous behavior of multiple-wave x-ray interaction at atomic resonance, the coherent multiple-wave x-ray interaction in charge-density wave materials.
Due to the sensitivity to the phases of the structural factors, the multiple-wave diffraction has found its unique application for the solution of the phase problem of x-ray optics, diffraction physics and crystallography. We have proposed some theoretical approaches to explain the phase sensitivity of multiple-wave diffraction, as well as developed the experimental techniques for quantitative determination of reflection phases for bulk crystals, surface layers, macromolecular crystals, charge-density waves, and phase shifts at at