Propagation of a partially coherent focused X-ray beam within a planar X-ray waveguide

A linear-transmission Fresnel-zone-plate lens is used for coupling a monochromatic X-ray beam of 13.2 keV into a planar X-ray waveguide. The zone plate focuses the beam parallel to the entrance of the waveguide, by which means a flux enhancement of a factor of 54 inside the waveguide is obtained. This substantially enlarges the range of X-ray diffraction experiments that can be performed on samples confined within the waveguide. The coherent properties of the beam, as obtained at a third-generation synchrotron facility, are investigated by comparing the experimental data with numerical calculations in which partial coherence is taken into account by propagation of the mutual intensity function. The conditions for which the X-rays travelling through the waveguide are coherent are discussed.