Enhancement of second-harmonic generation in metal islands close to a conducting surface

Abstract

The second-harmonic generation (SHG) in a layered system consisting of Ag-islands/SiOx spacer/Ag is investigated. The efficiency of this process depends strongly on the mass thickness d of the dielectric SiOx. An enhancement by a factor of 80 of the second harmonic (SH) of this system in comparison to the SH signal of an Ag-island film for p-polarized excitation and 50° angle of incidence was observed for a specific separation distance of 40 nm. We interpret this increase of the SH as being due to the strongly increased absorption at the fundamental frequency, caused by the excitation of localized surface plasmons and thin-film resonances in this layer structure. The theoretical description of the enhancement factor is in good agreement with the experimental results using stratified medium theory for modelling the thin-film system.