Amplification of surface plasmon polaritons in the presence of nonlinearity and spectral signatures of threshold crossover

TL;DR

This paper investigates how nonlinearity affects surface plasmon polaritons at a metal-amplifier interface, revealing stationary modes and spectral narrowing akin to laser threshold crossover.

Contribution

It derives a nonlinear dispersion law for SPPs and shows how gain saturation results in stationary modes and spectral changes, a novel insight into plasmonic nonlinear dynamics.

Findings

Stationary SPP modes form due to gain saturation.

Spectral narrowing occurs at the threshold crossover.

Nonlinear effects modify SPP propagation characteristics.

Abstract

We describe effects of nonlinearity on propagation of surface plasmon polaritons (SPPs) at an interface between a metal and an amplifying medium of the externally pumped two-level atoms. Using Maxwell equations we derive the nonlinear dispersion law and demonstrate that, the nonlinear saturation of the linear gain leads to formation of stationary SPP modes with the intensities independent from the propagation distance. Transition to the regime of stationary propagation is similar to the threshold crossover in lasers and leads to narrowing of the SPP spectrum.