Quantum cascade lasers for open- and closed-path measurement of atmospheric trace gases

J. Barry McManus; David D. Nelson Jr.; Joanne H. Shorter; Mark S. Zahniser; Antoine Mueller; Yargo Bonetti; Mattias Beck; Daniel Hofstetter; Jerome Faist

doi:10.1117/12.452093

23 September 2002 Quantum cascade lasers for open- and closed-path measurement of trace gases

J. Barry McManus, David D. Nelson Jr., Joanne H. Shorter, Mark S. Zahniser, Antoine Mueller, Yargo Bonetti, Mattias Beck, Daniel Hofstetter, Jerome Faist

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Proceedings Volume 4817, Diode Lasers and Applications in Atmospheric Sensing; (2002) https://doi.org/10.1117/12.452093
Event: International Symposium on Optical Science and Technology, 2002, Seattle, WA, United States

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, David D. Nelson Jr., Joanne H. Shorter, Mark S. Zahniser, Antoine Mueller, Yargo Bonetti, Mattias Beck, Daniel Hofstetter, and 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); https://doi.org/10.1117/12.452093

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