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1.9 THz Quantum-cascade Lasers with One-well Injector

We report terahertz quantum-cascade lasers operating predominantly at 1.90THz with side modes as low as 1.86THz (λ≈161μm, ℏω≈7.7meV). This is the longest wavelength to date of any solid-state laser that operates without assistance of a magnetic field. Carriers are injected into the upper radiative state by using a single quantum-well injector, which resulted in a significant reduction of free-carrier losses. The laser operated up to a heat-sink temperature of 110K in pulsed mode, 95K in continuous wave (cw) mode, and the threshold current density at 5K was ∼140A∕cm2.