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

Abstract

ABSTRACT Recently, we have demonstrated that the intrinsicŽ linewidth of Quantum Cascade Lasers (QCLs) can go beyondthe radiative lifetime of the upper level. This represents the “rst demonstration of a sub-radiative linewidth forany 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 suchintrinsic properties by designing appropriate phase-lock loops and enhancement-cavities for interaction withmolecules. Combination with optical-frequency-comb-synthesizers and appropriate spectroscopic techniques,like saturated-cavity-ring-down-SCAR or polarization spectroscopy can provide unprecedented sensitivity andfrequency accuracy for molecular detection.Keywords: Quantum Cascade Lasers, Frequency Metrology, Infrared Spectroscopy 1. INTRODUCTION Intersubband quantum cascade lasers (QCLs) have become well established light sources in the mid-infrared(IR) spectral region, with many applications reporting high-sensitivity trace-gas detection,