X-RAY-SCATTERING WITH PARTIAL COHERENT RADIATION - THE EXACT RELATIONSHIP BETWEEN RESOLUTION AND COHERENCE

We discuss the scattering of X-rays by matter using the Huygens-Fresne l method for the particular case of scattering from surfaces and inter faces. We discuss the exact relationship between ''coherence'' and ''i nstrumental resolution'' effects in various regimes. The so-called ''F raunhofer'' and ''Fresnel'' regimes are distinguished and it is shown that most X-ray experiments are performed in what we call the ''extrem e Fresnel'' regime. For each of those regimes the so-called ''incohere nt'' and ''coherent'' limits are discussed. We illustrate the results with explicit calculations for surface scattering from layered materia ls. (C) 1998 Elsevier Science B.V. All rights reserved.