Surface plasmon resonance enhanced second-harmonic generation in Kretschmann configuration

We report second-harmonic generation (SHG) from a thin gold film at surface plasmon resonance (SPR) in an attenuated total reflection (ATR) geometry having the Kretschmann configuration. The SHG intensity was observed to be 350-400 larger than the reflected SHG intensity in the Fresnel reflection geometry at the surface of the thin gold film. A similar enhancement was observed in the case of a thin gold film covered with a hemicyanine monolayer. These results suggest that the SHG source of the thin gold film is located outside this film. Simulation based on this model yields an enhancement factor of similar to 285, in agreement with the experimental results, whereas the simulation supposing that the SHG source is located inside the gold thin film gives a factor of over 6000. This model is consistent with a hydrodynamic model of SHG in a metal, in which the nonlinear current runs outside the bulk metal and the electron density penetrates from the metal to the air at their interface. (c) 2004 Elsevier B.V. All rights reserved.