Coherent optical coupling of plasmonic dipoles in metallic nanoislands with random sizes and shapes

Abstract

We study coherent optical coupling of localized surface plasmon resonances associated with metallic nanoislands (grains) with random sizes and shapes. This is done by investigating the optics of two-dimensional photonic lattices consisting of periodic regions containing such nanoislands. Hybridization of the plasmons associated with these islands with the photonic lattice modes is investigated as the sizes of the nanoislands are increased from tens of nanometers to a coalescing limit wherein each region becomes a solid metallic nanoantenna. We show that when the nanoislands are very small the hybridization process can generate a unique form of surface lattice resonances (SLRs). This suggests phase-correlated coupling of the inhomogeneous distribution of plasmonic dipoles with the diffractive modes of the lattice, leading to a significant enhancement of their optical cross section. Our results show that as the nanoislands become larger the nature of the surface lattice resonance is changed from orthogonal diffraction coupling of plasmon dipoles to parallel coupling of standing-wave plasmons (modes) formed in solid metallic nanoantennas. Emission intensity and dynamics of excitons in semiconductor quantum dots are used to probe the in-phase excitation of plasmons and the impact of refractive index is explored.