Resonant surface second harmonic generation from Au films on NaCl(100)

Abstract

We have found that the resonance energy of optical second-harmonic (SH) generation from Au films on NaCl(100) depends strongly on the film thickness. The resonance peak of the SH intensity was found at $2\ensuremath{\Elzxh}\ensuremath{\omega}=3.2\mathrm{eV}$ for the island film of mean thickness 0.4 nm, while it appeared at $2\ensuremath{\Elzxh}\ensuremath{\omega}=2.4\mathrm{eV}$ for the continuous film of thickness 40 nm. We suggest that the SH intensity peak observed at $2\ensuremath{\Elzxh}\ensuremath{\omega}=3.2\mathrm{eV}$ originates from a resonant transition from occupied to unoccupied electronic levels of the (100) surface on top of the Au islands. The SH intensity peak observed at $2\ensuremath{\Elzxh}\ensuremath{\omega}=2.4\mathrm{eV}$ for the film thickness of 40 nm originates from the roughness-induced linear dielectric property of the film.