Coulomb and quenching effects in small nanoparticle-based spasers

TL;DR

This study numerically investigates how mode mixing and dipole-dipole interactions affect spasing in small nanoparticle-based systems, revealing that direct dipole coupling hinders lasing threshold while mode mixing is negligible.

Contribution

It introduces a combined Maxwell-Bloch and Green's function approach to analyze the impact of dipole interactions and mode mixing on spasing in small composite nanoparticles.

Findings

Gain coupling to nonresonant modes has negligible effect on threshold.

Dipole-dipole interactions cause frequency shifts that hinder spasing.

A parameter space region allows spasing despite these effects.

Abstract

We study numerically the effect of mode mixing and direct dipole-dipole interactions between gain molecules on spasing in a small composite nanoparticles with a metallic core and a dye-doped dielectric shell. By combining Maxwell-Bloch equations with Green's function formalism, we calculate lasing frequency and threshold population inversion for various gain densities in the shell. We find that gain coupling to nonresonant plasmon modes has a negligible effect on spasing threshold. In contrast, the direct dipole-dipole coupling, by causing random shifts of gain molecules' excitation frequencies, hinders reaching the spasing threshold in small systems. We identify a region of parameter space in which spasing can occur considering these effects.