High-resolution,quasi-Fabry—Perot X-ray interferometer

An extremely simple X-ray interferometer is described that should provide resolutions (λ/Δλ) of more than 10⁵. It relies on the use of nonlocalized, quasi-Fabry—Pérot interference fringes, which are detectable when a widely divergent beam of X-rays from a point source is incident on a good quality crystal. The crystal has to have a suitable lattice spacing, and in the basic method described, must not exceed a certain thickness (or coherence length).