3.4-THz quantum cascade laser based on longitudinal-optical-phonon scattering for depopulation

We report the development of a quantum cascade laser, at $\text{λ=87.2\hspace{0.17em}μ}\mathrm{m},$ corresponding to 3.44 THz or 14.2 meV photon energy. The ${\mathrm{GaAs/Al}}_{\text{0.15}}{\mathrm{Ga}}_{\text{0.85}}\mathrm{As}$ laser structure utilizes longitudinal-optical (LO) phonon scattering for electron depopulation. Laser action is obtained in pulsed mode at temperatures up to 65 K, and at 50% duty cycle up to 29 K. Operating at 5 K in pulsed mode, the threshold current density is 840 A/cm², and the peak power is approximately 2.5 mW. Based on the relatively high operating temperatures and duty cycles, we propose that direct LO-phonon-based depopulation is a robust method for achieving quantum cascade lasers at long-wavelength THz frequencies.