Observation of phase change of X-ray polarizability by rocking curves in the Bragg case

Rocking curves of the reflected and transmitted beams for GaAs 600 in the symmetric Bragg case were measured just below the K-absorption edge of Ga using X-rays from synchrotron radiation. Asymmetry and its reversal of the rocking curves for the transmitted beam were observed: the rocking-curve intensity in the lower-angle region of the exact Bragg angle was larger than that in the higher-angle region when the X-ray energy was 9 eV below the edge, while the asymmetry was reversed when the X-ray energy was about 6 eV below the edge. The reversal has been found to result from the change in the phase of X-ray polarizability.