Parallel-beam coupling into channel-cut monochromators using curved graded multilayers

Abstract

Parabolically bent multilayers with laterally graded period were applied as condensing reflectors to convert divergent X-rays from laboratory X-ray sources into a parallel beam. Two different modes of coupling such a collimated beam into multi-reflection channel-cut monochromators for high-resolution X-ray diffractometry were tested. (i) Parallel coupling (the scattering vector of the mirror reflection is in the plane of the scattering vectors of the monochromator and the sample) enables one to exploit a wider solid angle range of the X-ray source and to gain nearly two orders of magnitude in intensity. (ii) Crossed coupling (the scattering vector of the mirror reflection is perpendicular to the scattering vectors of the monochromator and the sample) delivers a beam with much reduced vertical divergence. This eliminates the line broadening in rocking curve measurements even for strongly tilted samples.