Quantum Fountain Intersubband Laser at 15.5 μm Wavelength in GaAs/AlGaAs Quantum Wells.

Abstract

A new type of semiconductor unipolar laser operating in the mid-infrared spectral region, the Quantum Fountain intersubband laser, is demonstrated. It is based on optical pumping of a three-bound-state coupled quantum well structure in the GaAs/AlGaAs material system. The lasing transition occurs between the two excited states. Population inversion is achieved by benefiting from a LO-phonon resonance between the two lower subbands. The optical pumping scheme enables a simplified design of the active region as compared to electrically pumped intersubband lasers. Moreover, because doped layers and metallic contacts are not necessary for the operation of the Quantum Fountain laser, free-carrier absorptions can be minimized, thus allowing long-wavelength operation. Large optical gains are measured using pump-probe experiments with a free-electron laser. Lasing action has been achieved at a record long wavelength of 15.5 μm under optical pumping by a pulsed CO2 laser. The output peak power is of the order of 0.6 W at low temperatures.