Plasmons on Separated Particles: Homogenization and Applications

Abstract

In this chapter, we discuss localized plasmons in optical systems containing metallic particles, clusters of metallic particles, or periodic arrays of metallic particles, separated in all cases by a background dielectric material or matrix. We begin with a brief discussion of the equations governing electromagnetic propagation in structured or composite systems containing metal particles in a matrix. A full electromagnetic solution for a periodic array of particles or a finite cluster of them is possible, but much can be learned from treatments in the quasistatic approximation, where properties of the particles are subsumed in effective dielectric permittivities and magnetic permeabilities, and these are used in Maxwells’ equations for a homogeneous material to calculate reflection and transmission properties. The two most important equations used to calculate effective dielectric permittivities and magnetic permeabilities are the Maxwell-Garnett formula and Bruggeman’s effective medium formulae. We compare these in Sect. 6.3, and look at applications in Sect. 6.4 to the field of selective absorbers for photothermal and photovoltaic energy applications. In the next section, we go on to consider collections of particles and their resonant properties, which can be exploited to deliver strong local concentrations of electromagnetic fields. These are used in Sects. 6.6 and 6.7 to discuss cloaking using plasmonic resonance, and spasers, devices which can overcome through amplification the propagation losses associated with plasmons.