Quantum cascade laser turns extremely nonlinear

Collaborating with partners from Germany, France, UK and Sweden we observed high-order terahertz nonlinearities directly in a free-running quantum cascade laser. With field-resolved two-dimensional spectroscopy we revealed up to eight-wave-mixing processes in a regime of negative absorption as well as the laser’s sub-cycle gain dynamics. High-order nonlinearities of this kind have the potential for various future applications, ranging from efficient intracavity frequency conversion and mode proliferation to passive mode locking.

The results have been published in Light: Science & Applications.