Interference absorption line rejection procedures for tunable diode laser gas analyzers using digital sweep integration analysis techniques

Gary E. Kidd

doi:10.1117/12.452071

23 September 2002 Interference absorption line rejection procedures for tunable diode laser gas analyzers using digital sweep integration analysis techniques

Gary E. Kidd

Author Affiliations +

Proceedings Volume 4817, Diode Lasers and Applications in Atmospheric Sensing; (2002) https://doi.org/10.1117/12.452071
Event: International Symposium on Optical Science and Technology, 2002, Seattle, WA, United States

Abstract

Open path tunable diode laser gas analyzers are constrained by the interference absorption line features in the modulation wavenumber window or line overlap from peripheral absorption lines, which reduce accuracy in the estimates of object gas concentration and in the locking of the laser and absorption line center wavenumbers. To achieve greater potential resolution and smaller physical instrument size in gas analyzers for atmospheric sampling, laser wavelengths must increase to the 1.5-5 um mid-IR band where unfortunately density and line strength of interference absorption lines also increase. A systematic approach including digital methods is described to select the most suitable Hitran object gas lines in the presence of interference gases H₂O, CO₂, CH₄, and N₂O and record the set of interference lines about the object gas line. A method is described to decompose the sample absorbance spectrum as absorption feature amplitude-position data to compare with the recorded interference line data to identiy the object line and laser center wavenumber shift. The processes of automatic object gas line identity, interference absorbance spectrum synthesis and subtraction from the sample absorbance and of line-lock and concentration analysis from the resultant spectrum are detailed. Examples are presented to illustrate the expected accuracy and error bounds for a dual gas CO₂/H₂O analyzer.

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Gary E. Kidd "Interference absorption line rejection procedures for tunable diode laser gas analyzers using digital sweep integration analysis techniques", Proc. SPIE 4817, Diode Lasers and Applications in Atmospheric Sensing, (23 September 2002); https://doi.org/10.1117/12.452071

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