Long-range surface-plasmon modes in silver and aluminum films

We report the first observation to our knowledge of a sharp minimum in the attenuated total reflectivity of a thin metal film between index-matching layers. The resonance is due to the excitation of the long-range surface-plasmon mode on both sides of the thin metal films, as originally discussed by Sarid [Phys. Rev. Lett. 47, 1927 (1981)]. The angular widths of the observed resonance in silver and aluminum films are both reduced by over an order of magnitude relative to that associated with the Kretschmann excited mode.