A specific angular distribution of x rays from111In embedded in a thin‐film waveguide (Au film/Langmuir–Blodgett film/Au substrate) is observed by a non‐energy‐dispersive two‐dimensional detector (imaging plate). The angular distribution for the thickness of the upper Au layer of 90 A˚ can be explained by normal calculation of the optical electromagnetic wave solution of Maxwell’s equations for each interface and reciprocity. However, the angular pattern in the upper 400 A˚ Au thickness layer cannot be accounted for by the normal approach without considering the intensity of the x‐ray sheet beam emerging from the end of the multilayer. ©1995 American Institute of Physics.