How to manipulate the frequency of a Terahertz Quantum Cascade Laser

We investigate techniques to manipulate the frequency of Terahertz Quantum Cascade Lasers (THz QCL). Frequency tuning by changing the heatsink temperature or the QCL drive current, or by illumination of the QCL with bandgap light. Creation of frequency sidebands through amplitude modulation of the drive current or the bandgap light. We report the observation of strong difference frequency generation in a two-colour THz QCL and discuss the possibility to use this resonant non-linear effect to create (tunable) sidebands by mixing the radiation from an external (tunable) microwave source with the THz field inside the QCL cavity.