Analytical expression for Risken-Nummedal-Graham-Haken instability threshold in quantum cascade lasers

TL;DR

This paper derives a simple analytical expression for the RNGH instability threshold in quantum cascade lasers, aiding practical analysis of their dynamic behavior and aligning well with experimental data.

Contribution

The paper presents a closed-form analytical expression for the RNGH instability threshold in FP cavity QCLs, incorporating carrier gratings and diffusion effects, validated by numerical simulations and experimental data.

Findings

Analytical threshold expression matches numerical simulations.

Model predicts low second threshold in QCLs.

Results agree with experimental observations.

Abstract

We have obtained a closed-form expression for the threshold of Risken-Nummedal-Graham-Haken (RNGH) multimode instability in a Fabry-P\'erot (FP) cavity quantum cascade laser (QCL). This simple analytical expression is a versatile tool that can easily be applied in practical situations which require analysis of QCL dynamic behavior and estimation of its second threshold. Our model for a FP cavity laser accounts for the carrier coherence grating and carrier population grating as well as their relaxation due to carrier diffusion. In the model, the RNGH instability threshold is analyzed using a second-order bi-orthogonal perturbation theory and we confirm our analytical solution by a comparison with the numerical simulations. In particular, the model predicts a low second threshold in QCLs. This agrees very well with experimental data available in the literature.