Gain saturation effects in THz quantum cascade lasers

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