X-ray Bragg diffraction in asymmetric backscattering geometry

We observe three effects in the Bragg diffraction of x rays in backscattering geometry from asymmetrically cut crystals. First, exact Bragg backscattering takes place not at normal incidence to the reflecting atomic planes. Second, a well-collimated (similar or equal to 1 mu rad) beam is transformed after the Bragg reflection into a strongly divergent beam (230 mu rad) with reflection angle dependent on x-ray wavelength-an effect of angular dispersion. The asymmetrically cut crystal thus behaves like an optical prism, dispersing an incident collimated polychromatic beam. The dispersion rate is similar or equal to 8.5 mrad/eV. Third, parasitic Bragg reflections accompanying Bragg backreflection are suppressed. These effects offer a radically new means for monochromatization of x rays not limited by the intrinsic width of the Bragg reflection.