Characterization of x-ray spatial coherence and its propagation

Abstract

X-ray beams of varying degrees of partial spatial coherence have been prepared and characterized, and the diffraction of these beams from patterned surfaces measured. The experiments were carried out at a bending magnet source at the NSLS (X-19C). The resulting diffraction patterns for a pair of slits and an optical grating are analyzed in terms of an x-ray mutual coherence function used to describe the propagation of the coherent wave front in the visible light regime. The diffraction and speckle pattern from the surface are the result of the mutual coherence function convoluted with the interference function of the grating. Forming diffraction patterns, or x-ray speckles, with partially coherent x-rays relaxes the requirement for the interference, thereby increasing the ‘‘effective’’ coherent flux. This detailed knowledge of the propagation of the x-ray spatial coherence aids in defining the physical characteristics of beamline optical elements that must preserve the coherent x-ray wave front.