THz and sub‐THz quantum cascade lasers

In this paper we review recent progress in obtaining laser action from semiconductor quantum cascade structures covering the low THz region of the electromagnetic spectrum, from 2 THz (λ ≃ 155 μm) down to the sub‐THz region (λ > 300 μm). Particularly, laser active region designs based on bound‐to‐continuum transition and magnetically assisted intra‐well transition are presented. The wide scalability of active region designs is discussed and illustrated with experimental data. Latest results including the demonstration of laser action from quantum heterostructure at 950 GHz are presented.