Self-starting Harmonic Comb Emission in THz Quantum Cascade Lasers

TL;DR

This paper demonstrates robust, self-starting harmonic mode locking in Copper-based THz quantum cascade lasers, achieving stable combs over 600 GHz bandwidth at 80 K, with theoretical modeling supporting the experimental results.

Contribution

It reports the first demonstration of self-starting harmonic combs in Copper-based THz quantum cascade lasers with broad bandwidth and theoretical analysis.

Findings

Stable harmonic combs spanning over 600 GHz at 80 K

Self-starting harmonic mode locking achieved

Theoretical Maxwell-Bloch model explains the data

Abstract

Harmonic comb state has proven to be emerging in quantum cascade lasers and promoted by an interplay between parametric gain and spatial hole burning. We report here on robust, pure, self-starting harmonic mode locking in Copper-based double-metal THz quantum cascade lasers. Different harmonic orders can be excited in the same laser cavity depending on the pumping condition and stable harmonic combs spanning more than 600 GHz bandwidth at 80 K are reported. Such devices can be RF injected and the free running coherence is assessed by means of self-mixing technique performed at 50 GHz. A theoretical model based on Maxwell-Bloch equations including an asymmetry in the gain profile is used to interpret the data.