Crystal cavity resonance for hard x rays: A diffraction experiment

Abstract

We report the details of the recent x-ray back diffraction experiments, in which interference fringes due to x-ray cavity resonance are unambiguously observed. The Fabry-P\'erot type cavities, the tested crystal devices of reflectivity $R\ensuremath{\simeq}0.5$ and finesse $F\ensuremath{\simeq}2.3$, consist of monolithic two-plate and eight-plate silicon crystals. They were prepared by using x-ray lithographic techniques. The thicknesses of the crystal plates and the gaps between the two adjacent plates are a few tens to hundreds $\ensuremath{\mu}\mathrm{m}$. The (12 4 0) back reflection and synchrotron x-radiation of energy resolution $\ensuremath{\Delta}E=0.36\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at $14.4388\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ are employed. Interference fringes in angle- and photon-energy scans for two-plate and eight-plate cavities are shown. Considerations on the temporal and spatial coherence for observable resonance interference fringes using synchrotron x-rays are presented. The details about the accompanied simultaneous 24-beam diffraction in relation to x-ray photon energy are also described.