Quantitative determination of phases of X-ray reflections from three-beam diffraction. I. Theoretical considerations

A method of quantitative determination of X-ray reflection phases using three-beam multiple diffraction is described. This method is derived from the dynamical theory of X-ray diffraction. First-order approximation is employed to take care of the multi- beam diffraction situation. Polarization and excitation of wave fields and the Lorentz factor of crystal rotation are considered. For practical purposes, instrumental broadening and crystal mosaicity are included in calculating the diffraction intensity profiles. It is found that in the theoretical formulation the phase-dependent (dynamical) diffraction distribution can be separated from the phase-independent (kinematical) diffraction background. This makes possible the quantitative determination of reflection phases.