Self-starting harmonic comb emission in THz quantum cascade lasers

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