Gain and plasmon dynamics in negative-index metamaterials

TL;DR

This paper develops a rigorous theoretical model to study the interaction of light with metallic nanostructures and gain media in metamaterials, revealing conditions for loss compensation and insights into plasmonic mode formation.

Contribution

It introduces a comprehensive numerical framework for analyzing gain and plasmon dynamics in three-dimensional negative-index metamaterials, advancing design strategies for loss-compensated plasmonic devices.

Findings

Full loss compensation occurs when the real part of the effective refractive index becomes more negative.

The model captures nonlinear saturation, field enhancement, and radiative damping effects.

Internal processes significantly influence the optical properties of active metamaterials.

Abstract

Photonic metamaterials allow for a range of exciting applications unattainable with ordinary dielectrics. However, the metallic nature of their meta-atoms may result in increased optical losses. Gain-enhanced metamaterials are a potential solution to this problem, but the conception of realistic, three-dimensional designs is a challenging task. Starting from fundamental electrodynamic and quantum-mechanical equations we establish and deploy a rigorous theoretical model for the spatial and temporal interaction of lightwaves with free and bound electrons inside and around metallic (nano-) structures and gain media. The derived numerical framework allows us to self-consistently study the dynamics and impact of the coherent plasmon-gain interaction, nonlinear saturation, field enhancement, radiative damping and spatial dispersion. Using numerical pump-probe experiments on a double-fishnet metamaterial structure with dye molecule inclusions we investigate the build-up of the inversion profile and the formation of the plasmonic modes in the low-Q cavity. We find that full loss compensation occurs in a regime where the real part of the effective refractive index of the metamaterial becomes more negative compared to the passive case. Our results provide a deep insight into how internal processes affect the over-all optical properties of active photonic metamaterials fostering new approaches to the design of practical loss-compensated plasmonic nanostructures.