1.9 THz quantum-cascade lasers with one-well injector

We report terahertz quantum-cascade lasers operating predominantly at 1.90 THz with side modes as low as 1.86 THz (lambda approximate to 161 mu m, h omega approximate to 7.7 meV). 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 110 K in pulsed mode, 95 K in continuous wave (cw) mode, and the threshold current density at 5 K was similar to 140 A/cm(2).