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 ∼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.