Ignition of quantum cascade lasers in a state of oscillating electric field domains

TL;DR

This paper demonstrates that quantum cascade lasers can operate under inhomogeneous electric field domains, leading to lasing even in voltage regions traditionally avoided due to negative differential conductivity, supported by both theory and experiments.

Contribution

It reveals that QCLs can lase in NDC regions with inhomogeneous fields, challenging conventional design paradigms and enabling potential performance improvements.

Findings

Experimental observation of GHz oscillations before and after threshold.

Theoretical agreement with experimental data on domain-induced lasing.

Potential for optimized QCL design with reduced dissipation.

Abstract

Quantum Cascade Lasers (QCLs) are generally designed to avoid negative differential conductivity (NDC) in the vicinity of the operation point in order to prevent instabilities. We demonstrate, that the threshold condition is possible under an inhomogeneous distribution of the electric field (domains) and leads to lasing at an operation point with a voltage bias normally attributed to the NDC region. For our example, a Terahertz QCL operating up to the current maximum temperature of 199 K, the theoretical findings agree well with the experimental observations. In particular, we experimentally observe self-sustained oscillations with GHz frequency before and after threshold. These are attributed to traveling domains by our simulations. Overcoming the design paradigm to avoid NDC may allow for the further optimization of QCLs with less dissipation due to stabilizing background current.