Abstract

Surface-wave plasmon modes propagating over relatively long distances along thin metallic films have been reported and verified experimentally.^1,2 However, the conditions for exciting these waves most effectively by realistically bounded beams have not been explored in detail. We have therefore examined the fields produced by Gaussian beams incident on layered metal-film geometries used for guiding plasmon modes. Our analysis shows that the incident beam energy splits into a specularly reflected beam and a guided plasmon wave. To excite the plasmon mode most effectively, it is necessary to suppress the specular beam as much as possible. By utilizing a pole zero analysis of the reflectance function for layered configurations, we have found that this improvement can be achieved by placing a dielectric layer in parallel to the metallic film. A judicious choice of the physical parameters of the dielectric layer can couple most of the incident-beam energy into the plasmon wave and, in addition, it can considerably extend the propagation range of the plasmon mode.

© 1986 Optical Society of America