Analysis and Application of Multiple Diffraction Phenomena in Perfect Crystal Monochromators

Abstract

Since the introduction of EXAFS measurements using synchrotron radiation, experimentalists have been troubled by the occurrence of numerous dips in the primary intensity of the beam emerging from the monochromator system. These dips, or “glitches,” cause serious complications in the Fourier transform of EXAFS spectra. The physical source of this phenomenon, originally called the “Aufhellung Effect” and interesting in its own right, has been well understood since the early twenties: the intensity of the primary beam is modified by the presence of one or more secondary reflections satisfying Bragg’s law simultaneously. However, no universal way of analyzing and dealing with this effect has been proposed so far. In this note we first review and present a critical analysis of a sample of solutions of the problem and then discuss some potentially useful applications of glitches to the absolute energy calibration and precise geometric orientation of crystals.