Surface plasmon polariton scattering by a small particle placed near a metal surface: An analytical study

Abstract

Scattering of light by a small particle placed near a metal surface is studied via analytical calculations of the particle extinction cross section. Considering a small spherical particle, we express the extinction cross section via the total electric-field Green’s tensor of a metal-dielectric interface structure. Analytic expressions are derived for the parts of Green’s tensor that govern the excitation of p- and s-polarized waves propagating away from the interface, and waves propagating along and being localized at the interface, viz., surface plasmon polaritons (SPP’s). This allows us in turn to divide the extinction cross section into parts associated with scattering of light into different types of electromagnetic waves. The scattering cross sections related to SPP-to-SPP scattering, and scattering of SPP’s into waves propagating away from the interface, are studied with respect to the dielectric constant of the metal and the height of the scatterer above the interface. In the case where the light wavelength is close to the SPP resonance, the SPP-to-SPP scattering cross section can be orders of magnitude larger compared to the extinction cross section of a particle in free space, whereas in the case of a nearly perfect conductor, the SPP-to-SPP cross section tends to 0. The efficiency of SPP-to-SPP scattering is calculated and, e.g., for the metal dielectric constant-100 (order of magnitude for gold at the light wavelength 1500 nm) it is found to be above 60% for the optimum scatterer-surface distance. © 2004 The American Physical Society.