Controlling the emission of THz Quantum Cascade Lasers

The development of quantum cascade lasers (QCLs) operating at terahertz frequencies (THz) is proceeding at a very rapid pace. For their successful practical implementation, specific requirements have now to be addressed, particularly concerning the spectral properties of the emitted radiation. Single-mode THz lasers with external cavity have been achieved. Optical self-mixing has been observed in THz QCLs in the presence of an external cavity for insight into the linewidth enhancement.