Coherent propagation of x-rays in a planar waveguide with a tunable air gap

We have made a multimode waveguide of x rays having an air gap as the guidi ng medium. Individual transverse electric modes were found to propagate thr ough the planar waveguide with essentially no attenuation and with negligib le scattering losses to other modes. If different modes are excited simulta neously at the waveguide entrance, then the phase relation between these mo des as given by their propagation constants is found to be preserved over t he entire length of the waveguide.