Spontaneous emission of a two-level atom placed within clusters of metallic nanoparticles

Abstract

We present calculations of the electromagnetic local density of states and of thecorresponding spontaneous emission rate for a two-level atom placed near a metallicDrude-type nanosphere as well as within clusters of nanospheres. Our calculationsare based on a dyadic Green’s function formalism within the framework of themultiple-scattering method. We examine the convergence of the above quantitiesin terms of the angular expansion of the electromagnetic field. The frequencyand spatial dependence of the local density of states and of the correspondingspontaneous emission rate is also studied by depicting the relevant spectra for differentcluster sizes and configurations. We have found, in particular, that within thefrequency region of the surface–plasmon resonances the spontaneous emissionrate is influenced by the near field of the spheres which are closer to the atom,rendering the contribution of the farthest spheres almost negligible. Depending on thedistance from the surface of the sphere(s) the spontaneous emission rate in thecluster assumes values which can be several orders of magnitude larger than thecorresponding rate in a vacuum. Finally, we examine the differences which arise when anexperimentally available dielectric function is employed instead of the Drude type.