Quantifying the Selective Excitation-Free Enhancement of Chiral Plasmonic Nanocavities by Raman Scattering

Chiral plasmonic nanocavities are promising photonic components because they offer large electromagnetic field enhancement and display strong chiroptical responses. Herein we show that the Raman 2D band of graphene (graphite) can be used as a probe to quantify the selective "excitation-free" enhancement of chiral plasmonic nanocavities. Specifically, few-layer graphene and thin-film graphite are sandwiched in chiral Au nanocube-on-mirror structures, allowing their 2D bands to be modulated under the excitation of linearly polarized light. The chirality of the 2D band reflects the selective total enhancement of these structures but does not include contributions from the enhancement of the excitation rate. Our strategy provides a different perspective to assess the performance of chiral plasmonic nanocavities and will assist in their future improvement.