Signature of a Fano-resonance in a plasmonic meta-molecule's local density of optical states

TL;DR

This paper demonstrates how Fano resonances in plasmonic meta-molecules influence the local density of optical states, with implications for controlling spontaneous emission, through experimental measurements and analytical modeling.

Contribution

It provides the first experimental observation of LDOS redistribution at Fano resonances in plasmonic meta-molecules and offers a comprehensive analytical model explaining near- and far-field effects.

Findings

Fano resonance causes a spatial redistribution of LDOS.

A single eigenmode enhances radiative LDOS at the Fano dip.

Near- and far-field effects are explained by interference of eigenmodes.

Abstract

We present measurements on plasmonic meta-molecules under local excitation using cathodoluminescence which show a spatial redistribution of the local density of optical states (LDOS) at the same frequency where a sharp spectral Fano-feature in the extinction cross section has been observed. Our analytical model shows that both near- and far-field effects arise due to interference of the same two eigenmodes of the system. We present quantitative insights both in a bare state, and in a dressed state picture that describe plasmonic Fano interference either as near-field amplitude transfer between three coupled bare states, or as interference of two uncoupled eigenmodes in the far field. We identify the same eigenmode causing a dip in extinction to strongly enhance the radiative LDOS, making it a promising candidate for spontaneous emission control.