Narrow linewidth quantum cascade lasers as ultra-sensitive probes of molecules

Recently, we have demonstrated that the "intrinsic" linewidth of Quantum Cascade Lasers (QCLs) can go beyond the radiative lifetime of the upper level. This represents the first demonstration of a sub-radiative linewidth for any laser. The intrinsic linewidth of a QCL can be as narrow as hundreds Hz, paving new ways for ultra-sensitive and precise harnessing and detection of molecules. We are working towards full exploitation of such intrinsic properties by designing appropriate phase-lock loops and enhancement-cavities for interaction with molecules. Combination with optical-frequency-comb-synthesizers and appropriate spectroscopic techniques, like saturated-cavity-ring-down-SCAR or polarization spectroscopy can provide unprecedented sensitivity and frequency accuracy for molecular detection.