25 October 1999 Rapid-scan Doppler-limited absorption spectroscopy using mid-infrared quantum cascade lasers
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Abstract
Laser characteristics have been evaluated for mid-infrared quantum-cascade (QC) lasers operating in a continuous mode at cryogenic temperatures. These tests were performed to determine the suitability of QC lasers for use in various spectroscopic applications, including Doppler-limited molecular absorption spectroscopy and pressure-limited LIDAR instrumentation. Using rapid-scanning techniques, direct absorbance measurements of nitric oxide, ammonia and nitrous oxide have been performed with QC lasers, operating at either 5.2 or 8.5 micrometers . Measured Doppler-limited absorption profiles show no distortion with increased averaging (up to 103 - 104 samples averaged), thereby minimizing the need for sophisticated data acquisition systems which re- register successive data streams to accommodate for laser frequency jitter and drift. Additionally, the high tuning rates (2.5 cm-1 in 0.6 milliseconds; 5 - 10 kHz sweep repetition rate) achieved with the QC lasers allow for the measure of relatively rapid transient phenomena or a high degree of signal averaging in a short time. Noise- equivalent absorbances of 3 X 10-6 have also been obtained without optimizing the optical arrangement.
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Steven W. Sharpe, James F. Kelly, Richard M. Williams, John S. Hartman, Claire F. Gmachl, Federico Capasso, Deborah L. Sivco, James N. Baillargeon, Alfred Y. Cho, "Rapid-scan Doppler-limited absorption spectroscopy using mid-infrared quantum cascade lasers", Proc. SPIE 3758, Application of Tunable Diode and Other Infrared Sources for Atmospheric Studies and Industrial Processing Monitoring II, (25 October 1999); doi: 10.1117/12.366464; https://doi.org/10.1117/12.366464
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