Resonance quality, radiative/ohmic losses and modal volume of Mie plasmons
Molecular sytems are efficiently coupled to metal nanoparticles via the excitation of localized surface plasmons-polaritons (SPPs). The coupling strength between SPP and emitters can be estimated from the ratio Q/V where Q and V refer to the mode quality factor and effective volume, respectively. In this letter, we investigate in details the properties of Mie plasmons supported by a metallic nanosphere (Q-factor, radiative and ohmic losses, modal volume). We particularly focus on the difficulty to unambiguously define the modal volumes of localized SPPs. This leads us to propose two definitions; the first one is based on Purcell factor for a dipolar emitter in close proximity to the metallic nanoparticle and the second one is adapted from cavity quantum electrodynamics concept (cQED). This work brings simple hand tools to characterize the main properties of localized SPPs and will be helpful in designing optical nanosources. It also makes a bridge between cQED and quantum plasmonics.