Plasmon spectra of nanospheres under a tightly focused beam

TL;DR

This paper analyzes how tightly focused beams alter the plasmonic scattering and near-field enhancement of gold and silver nanospheres, revealing significant deviations from classical Mie theory especially at higher-order resonances.

Contribution

It provides an analytical solution using multipole expansion to study focusing effects on nanoparticle optical responses, highlighting differences from Mie theory.

Findings

Focusing significantly modifies far-field cross sections.

Near-field enhancement is affected by beam focusing.

Higher-order resonances show notable deviations from classical predictions.

Abstract

We study the modification of the far-field cross sections and the near-field enhancement for gold and silver nanospheres illuminated by a tightly focused beam. Using a multipole-expansion approach we obtain an analytical solution to the scattering problem and provide insight on the effects of focusing on the optical response. Large differences with respect to Mie theory are found especially when the nanoparticle supports quadrupole or higher-order resonances.