ENHANCED TOTAL REFLECTION WITH SURFACE-PLASMONS

The total internal reflectance of a homogeneous amplifying medium in contact with a thin silver film which is evaporated on a high-index prism is determined theoretically with the help of the Fresnel formulas. At the angle of incidence for surface-plasmon excitation the reflectance is reasonantly enhanced when the gain of the amplifying medium exceeds a value determined by the absorption of the metal film. For any value of gain above threshold there exists a thickness of the silver film for which the reflectance has a singular point. A device utilizing this resonance would be possible near 1 mu where the absorption of the silver is at a minimun and high-gain dyes are available.