Intensity interferometry for the study of x-ray coherence

Intensity interferometry has been performed for the study of x-ray coherence. A high-resolution monochromator at $E=14.41\mathrm{}\mathrm{keV}$ was developed for enhancing the interference signal. Transverse coherence profiles of undulator radiation were evaluated from measurements of mode numbers. The obtained coherence length in vertical, which is perpendicular to the scattering plane of the monochromator, was proportional to the distance from the light source, as is expected from the Van Cittert–Zernike theorem. Vertical emittances of the storage ring were determined from the measured coherence lengths. Degradation of transverse coherence with phase object was measured and analyzed based on the propagation law of mutual intensity.