Coupled surface plasmons in periodically corrugated thin silver films

We investigated experimentally the coupled modes of surface plasmons in periodically corrugated thin silver films in a thickness range from 26 to 121 nm. The films studied were self-supporting and corrugated with a period of 1888 nm and amplitudes varying from 6 to 12 nm, depending on the film thickness. Propagation and damping constants of the coupled modes in these films were determined from angle-scan photoacoustic measurements of the resonance absorption of 633-nm photons. Evidence was obtained which indicated that the presence of periodic corrugations was not the primary source of the observed difference between these constants and those in the planar films. The coupling efficiency of an incident photon to the coupled modes evaluated for a constant corrugation amplitude was found to be strongly dependent on film thickness.