Off-Resonance Enhancement of the Refractive Index via Indirect Optical Transitions

TL;DR

This paper demonstrates that off-resonance conditions can significantly enhance the refractive index in sub-5 nm gold nanoparticles by exploiting symmetry breaking and charge-carrier dynamics, surpassing traditional limits.

Contribution

It introduces a novel approach to boost the refractive index off-resonance in nanoscale media using electronic light scattering and symmetry considerations.

Findings

Refractive index can be locally enhanced off-resonance in gold nanoparticles.

Breaking spatial symmetry influences charge-carrier dynamics and RI.

ELS effectively probes RI variations in confined media.

Abstract

At resonance, the optical response of a homogeneous medium to incident light is governed by temporal dispersion, which induces changes in the refractive index (RI). However, recent experimental results reveal RI enhancements exceeding the fundamental limit of 5 in spatially confined systems. Herein, we study the off-resonance enhancement of RI in sub-5 nm gold nanoparticles using electronic light scattering (ELS). We discuss that the RI driven by the distribution and dynamics of excited-state charge-carriers can be locally boosted through the breaking of spatial symmetry in matter. These findings are critical for optically probing RI variations in spatially confined media using ELS.