Excess coincidences of reflected and refracted x rays from a synchrotron-radiation beamline

The coincidence rate between x rays reflected and refracted from a silicon crystal after a high-resolution monochromator was measured at the long undulator beam line of SPring-8. The data show excess coincidences relative to the random background, which vanish when the detectors of the reflected and refracted beams probe widely separated parts of the incoming x-ray wave front. The measured coincidence rate with different detector sizes and distances between the probed wave front positions, perpendicular to the scattering plane, agree well with fitting functions derived for the present experimental conditions. Furthermore, it is shown that the coincidence rate measured between probing positions in the scattering plane depends strongly on the angular spread of reflected and refracted x rays. Small angular spread is obtained by detuning from the exact Bragg condition, which results in good quantitative agreement of the coincidence data and theoretical predictions.

©2006 The American Physical Society