Raman scattering mediated by surface-plasmon polariton resonance

We have measured the enhanced Raman scattering by a liquid (methyl alcohol) in contact with an evaporated film of silver (∼400 Å) deposited on the flat surface of a hemispherical prism. The exciting laser light (5145 Å) was incident on the film through the prism and the scattered light from the liquid was collected also through the prism. The Raman-scattering intensity is a sharp function of both the incident and the scattered angles. The observed angular dependence of the Raman intensity can be fitted remarkably well by assuming that the enhanced scattering process is mediated by surface-plasmon polaritons at the silver-liquid interface. The observed scattering intensity is consistent with the predicted enhancement factor of 4 × ${10}^4$.