Surface-plasmon excitation of second-harmonic light: Emission and absorption

We aim to clarify the role that absorption plays in nonlinear optical processes in a variety of metallic nanostructures, and show how it relates to emission and conversion efficiency. We define a figure of merit that establishes the structure’s ability to either favor or impede second-harmonic generation. Our findings suggest that, despite the best efforts embarked upon to enhance local fields and light-coupling via plasmon excitation, nearly always the absorbed harmonic energy far surpasses the harmonic energy emitted in the far field. Qualitative and quantitative understanding of absorption processes is crucial in the evaluation of practical designs of plasmonic nanostructures for the purpose of frequency mixing.