Long-range surface mode supported by very thin silver films.

We report observations in the visible region of the spectrum, on a new coupled surface mode, the long-range surface exciton polariton which is supported by a highly absorbing thin layer. Using careful evaporation procedures it has proved possible to produce very thin islandized films of silver which have relative permittivities with real parts much less than their imaginary parts and which therefore satisfy the criterion necessary to support this new type of resonance