Mid-infrared detection of trace biogenic species using compact QCL based integrated cavity output spectroscopy (ICOS)

Abstract

Mid infrared Quantum Cascade (QCL) and Interband Cascade Lasers (ICL) coupled with cavity-enhanced techniques, have proven to be sensitive optical diagnostic tools for both atmospheric sensing as well as breath analysis. In this work, a TE-cooled, pulsed QCL and a cw ICL are coupled to high finesse cavities, for trace gas measurements of nitric oxide, carbon dioxide, carbon monoxide and ethane. QCL's operating at 5.26 μm and 4.6 μm were used to record ICOS spectra for NO, CO 2 , and CO. ICOS spectra of C 2 H 6 were recorded at 3.35 μm using an ICL. Ringdown decay times on the order to 2-3 μs are routinely obtained for a 50 cm cavity resulting in effective pathlengths on the order of 1000 meters. The sample cell is compact with a volume of only 60ml. Details of the QCL and ICL cavity enhanced spectrometers are presented along with the detection results for trace gas species. Here we report a detection limit of 0.7 ppbv in 4 s for NO in simulated breath samples as well as human breath samples. A preliminary detection limit of 250 pptv in 4 s for CO is obtained and 35 ppb in 0.4 s for C 2 H 6 .