Self-Consistent Theory of the Gain Linewidth for Quantum Cascade Lasers

TL;DR

This paper develops a self-consistent theoretical framework using nonequilibrium Green functions to analyze and predict the gain linewidth in quantum cascade lasers, highlighting conditions for linewidth reduction below lifetime broadening.

Contribution

It introduces a novel self-consistent theory for the gain linewidth in quantum cascade lasers, emphasizing the impact of the scattering environment on linewidth reduction.

Findings

Linewidth can be reduced below lifetime broadening with similar scattering environments.

The theory is particularly relevant for low-doped THz quantum cascade lasers.

The approach provides insights into linewidth control in quantum cascade laser design.

Abstract

The linewidth in intersubband transitions can be significantly reduced below the sum of the lifetime broadening for the involved states, if the scattering environment is similar for both states. This is studied within a nonequilibrium Green function approach here. We find that the effect is of particular relevance for a recent, relatively low doped, THz quantum cascade laser.