PRISM COUPLING TO LONG-RANGE COUPLED-SURFACE MODES

Using the virtual mode theory for attenuated total reflection (ATR) experiments the long-range coupled-surface modes supported by symmetrically bound thin films have been examined to study the influence of prism coupling. Approximate analytic results show that in certain circumstances prism coupling may result in a decrease of mode loss from the unperturbed eigenvalue. This is well illustrated for the long-range surface exciton-polariton. Detailed numerical evaluations confirm the analytic results. The generally accepted conclusion that prism coupling always results in an increase in mode loss is thus not supported by these results which show convincingly that for more complex ATR geometries simplistic treatments are invalid.