X-ray imaging of microobjects using dark field refraction-contrast method with resonantly absorbing multilayer mirrors

An x-ray multilayer mirror, specially designed to produce resonant absorption at a definite angle of incidence, may be used as an angular dispersive element for refractive x-ray radiography. In this method the signal-to-noise ratio can be significantly enhanced due to suppression of the shot noise produced by the direct beam. Refraction contrast of a copper wire 75 μm in diameter and a human hair was observed using Ni/C multilayer mirror with resonant absorption at CuKα radiation (1.54Å). The multilayer structure consisting of 30 bilayers was designed for CuKα radiation so as to have absorbing resonance of the width of about several arc seconds at a grazing angle of 0.8°. A monochromatic probe x-ray beam with a divergence of approximately 5 arc seconds was obtained from a conventional x-ray tube and a double crystal monochromator set in a strongly dispersive configuration. We have developed theoretical basis for this method, and have experimentally proven that it is possible to create critical components for its practical implementation: a multilayer mirror with resonant absorption, an x-ray imaging photon-counting detector with spatial resolution of about several micrometers, and a probe beam with the divergence of several arc seconds. This result proves the feasibility of x-ray refraction radiography using resonantly absorbing multilayer mirrors manufactured by conventional magnetron sputtering technology.