Electrodynamic coupling of electric dipole emitters to a fluctuating mode density within a nano-cavity

TL;DR

This paper explores how rotational diffusion affects the electrodynamic coupling of fluorescent molecules to a nanocavity, combining theory and experiments to improve understanding of fluorescence quantum yields.

Contribution

It introduces a theoretical framework and experimental approach to analyze the impact of rotational diffusion on molecule-cavity coupling.

Findings

Rotational diffusion significantly alters molecule-cavity coupling.

Theoretical model accurately predicts experimental results.

Method enables precise determination of fluorescence quantum yields.

Abstract

We investigate the impact of rotational diffusion on the electrodynamic coupling of fluorescent dye molecules (oscillating electric dipoles) to a tunable planar metallic nanocavity. Fast rotational diffusion of the molecules leads to a rapidly fluctuating mode density of the electromagnetic field along the molecules' dipole axis, which significantly changes their coupling to the field as compared to the opposite limit of fixed dipole orientation. We derive a theoretical treatment of the problem and present experimental results for rhodamine 6G molecules in cavities filled with low and high viscosity liquids. The derived theory and presented experimental method is a powerful tool for determining absolute quantum yield values of fluorescence.