Low-threshold terahertz quantum-cascade lasers

A quantum-cascade laser operating at $\text{λ=66\hspace{0.17em}μ}\mathrm{m}$ is demonstrated. It consists of a three-quantum-well chirped-superlattice active region embedded in a waveguide based on a single interface plasmon and a buried contact. A threshold current density of $\text{210\hspace{0.17em}}{\mathrm{A/cm}}^2$ at $\text{T=12\hspace{0.17em}}\mathrm{K},$ a maximum peak optical power of 4 mW, and operation up to $\text{T=44\hspace{0.17em}}\mathrm{K}$ are achieved in a 2.7 mm long device with a high reflectivity backfacet coating.