Gain saturation effects in THz quantum cascade lasers

Abstract

The effect of gain saturation in quantum-cascade structures with 2–4 quantum wells per period is herein analyzed on the basis of a system of balance equations. It is shown that the nonlinearity parameter decreases with an increase in the relaxation rate of laser levels, but the total current through the structure also increases. The use of the proposed multiphoton designs leads to a decrease in the non-linearity parameter without increasing the operating current. For example, in a two-photon scheme of laser transitions with the same transition probabilities and differential gains, two times slower saturation of the gain with an increase in the photon density is achieved, which leads to a high generation efficiency than in single-photon schemes.