Arrays of metallic particles may exhibit optical collective excitations known as surface lattice resonances (SLRs). These SLRs occur near the diffraction edge of the array and can be sharper than the plasmon resonance associated with the isolated single particle response. We have fabricated and modeled arrays of silver nanoparticles of different geometries. We show that square, hexagonal, and honeycomb arrays show similar SLRs; no one geometry shows a clear advantage over the others in terms of resonance linewidth. We investigate the nature of the coupling between the particles by looking at rectangular arrays. Our results combine experiment and modeling based on a simple coupled-dipole model.

We study regular wavelength scale arrays of metallic dimers. By employing dimers made up of two different sized discs, we are able to couple to array-based collective surface lattice resonances of both bright and dark, that is symmetric and antisymmetric, dimer modes and to show that the degree of asymmetry can be used to control the relative strength of the two surface-lattice modes. The collective nature of these excitations can even lead to an antisymmetric surface-lattice resonance that is stronger than the symmetric one; this is in stark contrast to the dark and bright nature of the underlying modes of the individual dimers. We verify these experimental findings, derived from extinction measurements, by comparison with both analytical and numerical modeling.

Abstract. We investigate the optical response of square arrays of metallic nanoparticles where each lattice site is occupied by two particles, a dimer. In particular we examine the surface lattice resonances arising in these structures when the inplane dipole moments associated with the plasmon modes of the nanoparticles couple together. The addition of a second particle to the basis leads to a more complex optical response, one that is anisotropic in the plane of the array. Extinction spectra are recorded at normal incidence for different orientations of the incident electric field. We compare our experimentally derived data with those from a coupled-dipole model. We show how the separation between the particles that comprise the dimer helps determine the overall response of the system.

Electromagnetic resonances are important in controlling light at the nanoscale. The most studied such resonance is the surface plasmon resonance that is associated with metallic nanostructures. Here we explore an alternative resonance, the surface exciton-polariton resonance, one based on excitonic molecular materials. Our study is based on analytical and numerical modelling. We show that periodic arrays of suitable molecular nanoparticles may support surface lattice resonances that arise as a result of coherent interactions between the particles. Our results demonstrate that excitonic molecular materials are an interesting alternative to metals for nanophotonics; they offer the prospect of both fabrication based on supramolecular chemistry and optical functionality arising from the way the properties of such materials may be controlled with light.