Non-exponential decay of dark localized surface plasmons

Area of Science:

• * Plasmonics and Nanophotonics
• * Quantum Optics and Light-Matter Interactions

Background:

• * Subwavelength plasmonic nanostructures exhibit radiative (bright) and non-radiative (dark) modes.
• * Conventional methods often approximate mode decay as exponential, using Markovian approximation.
• * Accurate characterization of mode lifetimes is essential for nanoscale optical applications.

Purpose of the Study:

• * To investigate the nonexponential decay of weakly coupled dark modes in plasmonic nanostructures.
• * To develop a theoretical framework accounting for strong dispersion and near-field feedback effects.
• * To provide accurate relaxation dynamics for improved device design and performance.

Main Methods:

• * Development of a theoretical framework introducing local relaxation degrees of freedom.
• * Modeling the decay of plasmonic modes considering material losses.
• * Macroscopic description of decay using a system-specific memory function derived from modal and material dispersions.

Main Results:

• * Demonstrated that the decay of dark plasmonic modes is strongly nonexponential.
• * Showed that conventional exponential relaxation times overestimate the actual mode lifetime.
• * Identified strong dispersion and near-field feedback as key factors influencing decay dynamics.

Conclusions:

• * The study reveals the limitations of the Markovian approximation for plasmonic nanostructures.
• * Accurate understanding of nonexponential decay is vital for optimizing applications like sensing, spasers, and quantum optics.
• * The developed theoretical framework offers a more precise method for analyzing plasmonic mode relaxation.