Coherent small-angle scattering on a bending-magnet beamline at the ESRF

A coherent X-ray beam is obtained from the D2AM bending-magnet beamline (BM 2) of the European Synchrotron Radiation Facility. As this line has permane nt convergent optics, monochromated by an Si(111) double monochromator, coh erence conditions are satisfied by selecting a part of the beam close to th e focal point. Low intensity (10(6) X-rays s(-1)) is partially compensated by a high degree of coherence and by the use of a high-resolution direct-il lumination CCD area detector. The stability of the small-angle set-up makes quantitative analysis possible. The calculated and measured degrees of coh erence are compared. The distributions of speckle intensities are explained by a beam composed of two-thirds coherent and one-third incoherent parts. This incoherent component is caused by Kapton windows, which will be remove d in future experiments.