Large spectral extinction due to overlap of dipolar and quadrupolar plasmonic modes of metallic nanoparticles in arrays

Christopher P Burrows,William L Barnes

doi:10.1364/oe.18.003187

Abstract

We explore the optical response of two-dimensional (2D) arrays of silver nanoparticles, focussing our attention on structures for which the individual particles in isolation support both dipolar and quadrupolar localised surface plasmon modes. For individual spheres we show that when dipolar and quadrupolar modes are excited simultaneously, interference leads to most of the scattered light being radiated in the forward direction. This is in contrast to what happens when each mode is excited on its own. We further show, using finite-element modelling that when such particles are assembled into square 2D arrays, the dipolar and quadrupolar modes can combine to produce a single peak in the optical density of the array. By simulating the field distributions associated with these modes we are able to illustrate the dual-mode character of this feature in the optical density. We have extended our examination of this effect by considering how the optical density of these arrays changes with incident angle for two polarisations (s and p).

Highlights

The scattering of light by metallic nanoparticles has seen a recent resurgence of interest in the field of plasmonics [1, 2]
We have shown that for individual particles, the dipolar and quadrupolar modes both contribute to the far-field angular scattering profile at the quadrupole frequency, and the resulting preferential forward scattering occurs as a result of constructive interference of the radiation of the two modes in the forward direction and destructive interference in the backward direction
Finite-element modelling has provided results which show that the collective behaviour of a square array of 100 nm diameter silver nanospheres surrounded by glass can differ strongly from the behaviour of individual nanospheres

Summary

Introduction

The scattering of light by metallic nanoparticles has seen a recent resurgence of interest in the field of plasmonics [1, 2]. Sub-wavelength arrays of metal nanostructures are fascinating owing to the greater range of phenomena they exhibit [3,4,5,6,7,8]. They form the basis of some of the structures pursued in the development of electromagnetic metamaterials [9]. The optical properties of arrays of metal nanoparticles have been studied before, most studies are concerned only with dipolar modes, higher order modes are less studied, and often ignored. We extend our discussion to examine the optical response of square, 2D arrays of silver nanospheres

Localised surface plasmon modes of individual metal nanospheres

Interparticle coupling in 2D arrays of metal spheres

Varying the incident angle

Summary