Enhancing second harmonic generation in gold nanoring resonators filled with lithium niobate.

Plasmonic nanorings provide the unique advantage of a pronounced plasmonic field enhancement inside their core. If filled with a polarizable medium, it may significantly enhance its optical effects. Here, we demonstrate this proposition by filling gold nanorings with lithium niobate. The generated second harmonic signal is compared to the signal originating from an unpatterned lithium niobate surface. Measurements and simulation confirm an enhancement of about 20. Applications requiring nanoscopic localized light sources like fluorescence spectroscopy or quantum communication will benefit from our findings.