Giant frequency-selective near-field energy transfer in active--passive structures

TL;DR

This paper demonstrates that combining gain and near-field effects in structured materials can significantly enhance energy transfer, enabling tunable and efficient energy extraction below lasing thresholds.

Contribution

It introduces a semianalytical approach to study amplified spontaneous energy transfer in active-passive structures, revealing optimal conditions for enhancement.

Findings

Orders of magnitude ASET enhancement below lasing threshold

Enhancement depends on geometry and gain tuning

Optimal configurations enable efficient energy extraction

Abstract

We apply a fluctuation electrodynamics framework in combination with semianalytical (dipolar) approximations to study amplified spontaneous energy transfer (ASET) between active and passive bodies. We consider near-field energy transfer between semi-infinite planar media and spherical structures (dimers and lattices) subject to gain, and show that the combination of loss compensation and near-field enhancement (achieved by the proximity, enhanced interactions, and tuning of subwavelength resonances) in these structures can result in orders of magnitude ASET enhancements below the lasing threshold. We examine various possible geometric configurations, including realistic materials, and describe optimal conditions for enhancing ASET, showing that the latter depends sensitively on both geometry and gain, enabling efficient and tunable gain-assisted energy extraction from structured surfaces.