Near-Field Coupling in Plasmonic Nanoarrays: Tailoring Radiative and Non-Radiative Losses Through Gap Engineering

Abstract

Absorption losses in plasmonic nanoparticles limit their performance in many optical and photonic applications by dissipating energy as heat and damping resonance strength. Using finite-difference time-domain simulations, we demonstrate that near-field coupling in dense, periodic nanoparticle arrays can significantly mitigate these losses. When interparticle distances are small, for the free carriers inside a given particle, the field enhancement of neighbouring particles reduces the effect of the field enhancement at the tip of the particle under study. As a result, the internal electric field – and thus the associated Ohmic losses – are substantially reduced, despite intense field enhancement in the narrow interparticle gaps. By comparing our results to the analytical theory of electric dipole arrays, we show that engineering the gaps in periodic arrays allows fine-tuning of the non-radiative to radiative losses ratio. This interplay between the near-field enhancement and the electric field within the nanoparticles suggests a route to exploit densely packed plasmonic arrays for optical devices, achieving high resonance strength and field enhancement while minimising thermal losses and associated damping. Furthermore, our results indicate the potential for decoupled control of hot-electron injection and thermal heating, offering new opportunities for the design of efficient plasmonic systems.