Tailoring Risken-Nummedal-Graham-Haken instability in quantum cascade lasers

MIR range Quantum Cascade Lasers (QCLs) find various sensing applications in security, health, gas sensing and spectral gas analysis. After some additional design and fabrication efforts, single mode or narrow band QCLs (DFB or grating-stabilized on external cavity) provide a direct access to spectral measurements of molecular fingerprints (ro-vibrational bands). However the simplest Fabry-Perot (FP) cavity QCLs often show extremely broad-band emission caused by a multimode Risken-Nummedal-Graham-Haken (RNGH) instability [1]. Although such incoherent multimode combs have been shown to find application in comb spectroscopy [2], the origin of low-threshold multimode RNGH instability in QCLs remain debated [1, 3] and, little is certain about approaches on tailoring the multimode behavior of FP QCL devices for specific application needs.