MODE-MIXING IN AN X-RAY THIN-FILM WAVE-GUIDE

Mode-mixing in a thin-film x-ray waveguide with 4-6 Angstrom interfaci al roughness was analyzed using a formalism based on the coupled power theory for optical waveguides. The mode mixing was found to occur bet ween nearest-neighbor modes with a uniform probability of similar to 1 .1% per bounce. The small mixing probability and the nearest-neighbor selection rule are consistent with a mixing mechanism arising from dif fuse scattering, which at subcritical angles of incidence displays dra matically different behavior in x-ray waveguides than in optical count erparts.