X-RAY SPECKLES FROM AN OPTICAL GRATING

We report a study of speckles produced by x rays of partial transverse coherence scattered from the surface of an optical reflection grating . This study reveals the presence of surface inhomogeneity that is und etectable with either laser (visible) light or transversely incoherent x rays. Qualitative analysis of the speckle patterns provides us with information on the surface morphology of the optical grating. The und erlying order due to the periodicity of the grating enhances the detec tion of the x-ray speckles. The speckle patterns are obtained using a well-characterized partially transverse-coherent source (a secondary s ource) produced with an arrangement of slits and a focusing mirror in a synchrotron x-ray beamline. The degree of transverse coherence is me asured and compared quantitatively with statistical optics predictions for the complex-coherence factor. [S0163-1829(98)08835-3].