In Depth Investigation of Lattice Plasmon Modes in Substrate-Supported Gratings of Metal Monomers and Dimers
Résumé
We study theoretically and numerically bidimensional square gratings of monomers and dimers of gold nanocylinders supported on a dielectric substrate, under plane wave illumination as a function of the angle of incidence and of the polarization. The number of parameters investigated makes that system a rich platform for the investigation of how grating coupling, and in particular edge diffraction which corresponds to the grazing propagation of a particular diffracted order, influence the surface plasmons response of nanoparticles. In particular, the considered periods are comparable to the range of incident wavelength, which makes the interpretation of the observed phenomena complex due to the large number of diffraction orders coming into play. In order to analyze those systems, we perform exact numerical simulations using Green’s tensor method, and compare them to a simplified approach based on the coupled-dipole approximation. The systematic identification of the grazing diffracted orders, combined with the computation of the S-matrix components, leads to better understanding of the different types of profiles (sharp maxima or angular minima) observed in the extinction spectra around the Rayleigh wavelengths associated with grazing diffraction in air or glass. The analysis is supported by computation of several electric field distributions computed for selected parameters.