Plasmonic surface lattice resonances in nanoparticle arrays

This article reviews the literature and provides a detailed computational analysis of the optical properties of one- and two-dimensional arrays of silver and gold nanoparticles, with an emphasis on surface lattice resonances (SLRs) that arise when localized plasmon resonances (LSPRs) in the nanoparticles couple to diffraction resonances that are determined by the interparticle spacing to give polariton modes in which the two types of excitations are coherently coupled. The computations are based on the coupled-dipole approximation, which provides a nearly quantitative description of the extinction spectra for arrays of this type where the particles are well separated and not too large. The computations are used to determine many characteristics of SLRs associated with the lower polariton mode that is mostly photonic in nature, and we also study the upper polariton that is dominated by the LSPR response, as well as Rayleigh anomalies (RAs) that correspond to purely diffractive excitation. The calculations explore the sensitivity of these excitations to the directions of the incident wave and polarization vectors relative to the array axis, the effect of array spacing and number of particles in the array, and the effect of nanoparticle radius and background refractive indices. Details of the physical mechanisms involved in determining blue- and/or redshifts as structural parameters are varied is provided, with SLRs being sensitive to far-field coupling, while LSPRs can also be sensitive to near- and intermediate-field interactions that in some cases are similar to effects found in dye molecule aggregates.

This study describes the optical behavior of one- and two-dimensional arrays of plasmonic silver and gold nanoparticles, based on the coupled-dipole approximation of electrodynamics. A new interpretation is provided for characterizing the optical resonances in such structures, including the identification of both upper and lower polaritons that couple Bragg diffraction modes and localized plasmons. Also, Rayleigh anomalies (Bragg modes not coupled to plasmons) are often but not always present in competition with the lower polariton mode. Connections to strong coupling effects and to plasmonic lasers are briefly discussed.