Plasmonic surface lattice resonances in arrays of metallic nanoparticle dimers

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 in-plane 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. (paper)