A planar x-ray waveguide with a tunable air gap for the structural investigation of confined fluids

A tunable x-ray waveguide with an air gap as the guiding medium is presented. Discrete transverse-electric modes excited in the air gap propagate almost undisturbed. Filling the air gap with a fluid allows for studies of ordering phenomena in a confined geometry. Since the guided modes are mainly confined to the guiding layer, background scattering from the plates is very low. Starting from the propagation characteristics of the modes in the empty waveguide, requirements on the x-ray source and on the positioning accuracy of the plates are derived. The construction of the waveguide is described and measurements of the far-field angular distributions of intensity exiting the waveguide are presented which illustrate the waveguide's properties. (C) 2000 American Institute of Physics. [S0034-6748(00)03904-6].