23 September 2002 Quantum cascade lasers for open- and closed-path measurement of trace gases
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Abstract
We report the application of quantum cascade (QC) lasers to measurement of atmospheric trace gases in both closed path and open path configurations. The QC laser, a recently available commercial device, is Peltier cooled and pulsed, with emission near 965 cm-1. We use direct absorption with a rapid sweep integration and spectral fits to derive absolute concentrations from tabulated line parameters without calibration. In the closed path configuration, with absorption in a long pathlength multipass cell (210 m, 50 Torr), we examined laser line widths and sensitivity limits. We measured ammonia with a precision of 0.05 nmole/mole (0.05 ppbv) RMS at 1 Hz, limited by detector noise. The laser linewith was 0.007 cm-1 HWHM, based on measurements of ethylene absorption line shapes with a current pulse width of ~14 ns. In the open path configuration, we measured ammonia in the exhaust of automobiles driving through a probe beam. Atmospheric pressure line broadening and turbulence limit the sensitivity, giving a column density noise level at 20 Hz of 1.4 ppm-m. We observed ammonia column densities up to 40 ppm-m in the exhaust plumes. In future systems we will include a CO2 channel, allowing normalization to fuel use rate.
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J. Barry McManus, J. Barry McManus, David D. Nelson, David D. Nelson, Joanne H. Shorter, Joanne H. Shorter, Mark S. Zahniser, Mark S. Zahniser, Antoine Mueller, Antoine Mueller, Yargo Bonetti, Yargo Bonetti, Mattias Beck, Mattias Beck, Daniel Hofstetter, Daniel Hofstetter, Jerome Faist, Jerome Faist, } "Quantum cascade lasers for open- and closed-path measurement of trace gases", Proc. SPIE 4817, Diode Lasers and Applications in Atmospheric Sensing, (23 September 2002); doi: 10.1117/12.452093; https://doi.org/10.1117/12.452093
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