Fig. 7: Phase matching and nonlinear susceptibility between mmWave and THz emission.
From: Millimeter wave photonics with terahertz semiconductor lasers
a Electric field as a function of time for both mmWave (red curve, filtered response of THz spectrum) and THz emission (blue) over a short time window illustrating the phase matched process between the two emission bands, b Modulus of second-order nonlinear susceptibility χ(2) as a function of THz excitation energy, calculated from the QCL bandstructure, showing the exalted giant nonlinearity.
