A monolithic X-ray monochromator with fixed exit beam position

Abstract

To avoid the inconvenient lateral movement of the monochromated beam in conventional, monolithic monochromators while the wavelength is changed, a new approach has been made. In principle the device is a channel cut single crystal where the walls of the groove are curved in such a way that the parallel displacement between the incoming and outgoing beams is independent of the wavelength. The analytical description of the shape of the mirrors is derived and different designs are discussed. Restrictions due to the asymmetric reflections are pointed out. The influence of deviations from the exact geometry are investigated as well as the consequences of misalignments with respect to the primary beam. Finally the successful fabrication with support by the CANON company and the first operation in the beam of the Photon Factory are reported. The result of an EXAFS experiment using this monochromator is presented.