Delocalized Lattice Plasmon Resonances Show Dispersive Quality Factors.

This Letter describes how out-of-plane lattice plasmon (OLP) resonances in 2D Au nanoparticle (NP) arrays show dispersive quality factors. These quality factors can be tailored simply by controlling NP height. Numerical calculations of near-field optical properties and band diagrams were performed to understand the measured dispersion effects of the OLPs. The results revealed that delocalized OLPs are a type of surface Bloch mode composed of many Bloch harmonics. As the OLP dispersion evolves from a stationary state to a propagating state, the nonradiative loss decreases because of weak local field confinement, whereas the radiative loss increases because of strong coupling to the leaky zero-order harmonic.