title: Gain and plasmon dynamics in active negative-index 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 a 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 overall optical properties of active photonic metamaterials fostering new approaches to the design of practical, loss-compensated plasmonic nanostructures.
authors.affiliation: Department of Physics, South Kensington Campus, Imperial College London, London SW7 2AZ, UK.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wuestner
authors.forename: Andreas
authors.initials: A
authors.lastname: Pusch
authors.forename: Kosmas L
authors.initials: KL
authors.lastname: Tsakmakidis
authors.forename: Joachim M
authors.initials: JM
authors.lastname: Hamm
authors.forename: Ortwin
authors.initials: O
authors.lastname: Hess