Diffractive-refractive optics: Focus size of sagittally focusing X-ray monochromator

Abstract

A sagittally focusing X-ray crystal monochromator based on diffractive–refractive optics is a four-crystal (+,−,−,+) monochromator with parabolic longitudinal grooves on the crystals surface. Such a monochromator is simultaneously able of focusing and monochromatizing a white beam. The focusing was experimentally proved in earlier papers but the size of the focus was always larger than expected. This discrepancy has not been properly discussed. Such a discussion is presented in this paper.