X-ray Resonance in Crystal Cavities--Realization of Fabry-Perot   Resonator for Hard X-rays
  X-ray back diffraction from monolithic two silicon crystal plates of 25--150 um thick and a 40--150 um gap using synchrotron radiation of energy resolution deltaE=0.36 meV at 14.4388 keV shows clearly resonance fringes inside the energy gap and the total-reflection range for the (12 4 0) reflection. This cavity resonance results from the coherent interaction between the X-ray wavefields generated by the two plates with a gap smaller than the X-ray coherence length. This finding opens up new opportunities for high-resolution and phase-contrast X-ray studies, and may lead to new developments in X-ray optics. 
S.-L. Chang (1 and 2), Yu. P. Stetsko (2), M.-T. Tang (2), Y.-R. Lee   (1), W.-H. Sun (1), M. Yabashi (3) and T. Ishikawa (3...