Minimum number of stages in a GaAs/AlGaAs terahertz quantum cascade laser with a metal-to-metal waveguide

Subject of study. The absorption coefficient of a metal-to-metal waveguide in a terahertz quantum cascade laser based on GaAs/AlGaAs heterostructures is studied. Aim of study. A theoretical study is performed to determine whether it is possible to significantly reduce the number of stages (the thickness of the active region) in terahertz quantum cascade lasers based on two previously implemented cascade designs with high-gain GaAs/AlGaAs heterostructures with quantum wells and a metal-to-metal waveguide. Method. The absorption coefficient of the metal-to-metal waveguide is numerically calculated using a transfer-matrix method based on Maxwell's equations. Main results. The absorption coefficient of a metal-to-metal waveguide in a terahertz quantum cascade laser is calculated as a function of the number of stages in the laser. We show that, for a laser with a gain of 200 cm-1 - 1 at a temperature of 100 K, only five stages are required for lasing to occur with a total waveguide thickness of 428 nm. Practical significance. Calculations show that it is possible to significantly reduce the thickness of the active region and the number of stages in a terahertz quantum cascade laser, which should simplify development of such a laser and lead to wider use of such lasers. (c) 2024 Optica Publishing Group