Self-excitation of surface plasmon polaritons

TL;DR

This paper predicts and develops a theory for the self-excitation of surface plasmons in a nanocavity, revealing a positive feedback mechanism that causes field instability without stimulated emission.

Contribution

It introduces the concept of self-excitation of surface plasmons in a nanocavity and derives analytical criteria for the threshold and frequency of self-oscillation from first principles.

Findings

Self-excitation of surface plasmons can occur in a nanogap cavity with polarizable inclusions.

A threshold condition for self-excitation is analytically derived.

The mechanism involves positive feedback without stimulated emission, unlike SPASERs.

Abstract

The novel effect of self-excitation of surface plasmons (SESP) in a plasmonic nanocavity is predicted and its theory is developed from first principles. It is assumed that the cavity is formed by a nanogap between two metals and contains polarizable inclusions. Basing on the dyadic Green's function of the structure, the equations for the field in the cavity are investigated. It is shown that under certain conditions the field becomes unstable that leads to its self-excitation. The threshold criterion for self-excitation as well as the frequency of self-oscillation are derived in an analytical form. The SESP effect is explained in terms of a positive feedback for the polarization of inclusions provided by the field reflected from the cavity walls. Such a mechanism does not imply stimulated emission that distinguishes it from SPASER or plasmon laser.