Three-level Spaser System: a Semi-Classical Analysis

TL;DR

This paper presents a semi-classical analysis of a nanospaser system with a three-level gain medium, revealing how relaxation processes influence threshold and plasmon generation, with a quadratic gain dependence.

Contribution

It introduces a three-level gain model for nanospasers, extending beyond the traditional two-level approach to include relaxation effects on operation.

Findings

Relaxation processes affect spaser threshold and plasmon number.

Plasmon number dependence on gain becomes quadratic in the three-level model.

Finite relaxation times significantly influence spaser dynamics.

Abstract

We theoretically study a nanospaser system, which consists of a spherical silver nanoparticle embedded inside a sphere composed of dye molecules. The gain of the system, dye molecules, are described by a three-level model, where the transition frequency between the lowest two energy levels is close to the surface plasmon frequency of the nanosphere. Contrary to a two-level model of spaser, the three-level model takes into account finite relaxation time between the high energy levels of the gain medium. These relaxation processes affect both the spaser threshold and the number of generated plasmons in the continuous wave regime. While for a two-level model of a spaser the number of generated plasmons has a linear dependence on the gain, for the three-level model this dependence becomes quadratic.