Mid-infrared cavity-enhanced absorption sensor for ppb-level N 2 O detection using an injection-current-modulated quantum cascade laser

Abstract

We report a mid-infrared cavity-enhanced absorption sensor for atmospheric nitrous oxide (N 2 O) detection using a continuous-wave distributed-feedback quantum cascade laser (DFB-QCL) at 4.5 µm. The QCL beam is coupled to a short (78 mm) Fabry-Pérot (F-P) optical cavity, which consists of two plano-concave dielectric mirrors with a reflectivity of 99.84%. The Pound-Drever-Hall technique is used to lock the QCL to the optical cavity by directly modulating the injection current of the QCL at 4 MHz. Our mid-infrared gas sensor achieves a minimum detection limit of 0.32 ppb at 50 s integration time. We demonstrate a proof-of-concept absorption spectral measurement of ambient air. Our study provides a promising way of developing compact and sensitive gas sensors for environmental monitoring.