Optical characterisation of thin metal film using surface plasmons resonance

The concept of surface plasmons originates from the application of Maxwell's to plasma whereby, the free electrons of a metal are treated as an electron fluid of high density (plasma). The density fluctuations occurring on the surface of such a fluid are called surface plasmons. Optical excitation of plasmons is not possible by direct impact of light on a metallic surface, so a prism coupling arrangement is needed. One possibility is to use a Kretschmann configuration [1] in which a p-polarized, collimated light beam passing through a glass prism undergoes total internal reflection (TIR) at glass-thin-metal film-dielectric interface. In this set-up plasmons are excited by (TIR) associated an evanescent wave after penetrating up to the metal-dielectric boundary. The surface plasmon resonance condition is given as,