Estimation of coherence properties of an undulator-generated x-ray beam from near-field and far-field slit diffraction visibilities

Abstract

We report on the study of hard x-ray diffraction by slits from the Fresnel to the Fraunhofer regime. The dark spot, i.e., the position where a minimum of intensity is found in the center of the diffraction pattern, is clearly observed. By progressively tuning the degree of coherence of the incident beam, the effect of partial coherence on the diffraction patterns is studied. We show that the transverse coherence length can be deduced with a good accuracy from the visibility of fringes in the Fraunhofer regime. We also show that a good estimation of the transverse coherence length can be obtained from measurements in the Fresnel regime. The measurements are discussed in the framework of the Gaussian Schell-model. A high degree of coherence is reached at the sample position for a beam size of a few micrometers and allows high-quality coherence experiments.