Asymmetrically cut crystals as optical elements for coherent x-ray beamconditioning

Abstract

The influence was studied of the asymmetric reflection from a perfect crystal on the coherence of x-rays produced by a synchrotron source of radiation. An analysis of single- and double-crystal set-ups is presented along with experimental measurements. The experiments were performed at the European Synchrotron Radiation Facility beamlines, namely Optics Beamline BM5 situated on a bending magnet, and ID22 using undulator radiation. A virtual source created by an asymmetric crystal was probed using an interferometry technique based on boron fibre. It is shown that an asymmetrically cut single crystal spoils coherence because of the spectral dispersion. The conditions required to preserve coherence in a double-crystal set-up are obtained theoretically, and proved experimentally. In the case of symmetrical reflection the requirements on an allowable miscut between the crystal surface and the lattice planes are derived.