COHERENCE PROPERTIES OF X-RAY POINT FOCUSING WITH FLAT CRYSTALS IN MODULATED STRUCTURES

Coherence properties of an x-ray point focusing method, using Aat crys tals with modulated structures, are presented. The diffraction limit o f the optics is derived for a given monochromatic point source. Within the energy range 8-16 keV, Si (111) and quartz (110) reflections are used to demonstrate the minimum achievable focus sizes to be 0.058 and 0.18 mu m, corresponding to the source sizes of 5 and 13 mu m, respec tively. Calculations of the distribution of the Bragg diffraction ampl itude indicate that the focusing method is web suited for synchroton r adiation sources. The criteria for achieving minimum focus size, when an x-ray source with a finite source size and a wavelength spread is c onsidered, are obtained based on the concept of the spatial coherence length. (C) 1997 Optical Society of America.