An off-axis cavity-enhanced absorption spectrometer at 1605 nm for the 12CO2/13CO2 measurement |
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| Authors: | VL Kasyutich PA Martin RJ Holdsworth |
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| Institution: | (1) School of Chemical Engineering and Analytical Science, University of Manchester, PO Box 88, Manchester, M60 1QD, UK;(2) TDL Sensors Ltd, School of Chemical Engineering and Analytical Science, University of Manchester, PO Box 88, Manchester, M60 1QD, UK |
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| Abstract: | A distributed feedback diode laser sensor based upon off-axis cavity-enhanced absorption spectroscopy at 1605.5 nm has been developed for 13C16O2/12C16O2 isotope ratio measurements in synthetic air and human breath. A noise-equivalent absorption sensitivity of 3.9×10-10 cm-1 Hz-1/2 has been determined for a cavity base length of 28.2 cm and averaging 4000 scans within 8.688 s. For 5% CO2 concentration measurements, δ13C standard deviations of 1.8 ‰ and 3.7 ‰ have been estimated for five successive measurements based on peak height and integrated area estimations at 107.9 Torr, respectively. The contributions of amplified spontaneous emission of the laser and a radiation that is spatially uncoupled into the cavity mode have been described for cavity transmittance measurements. The limitations of the developed sensor and further steps towards precision and accuracy improvements are discussed. PACS 42.55.Px; 39.30.+w; 42.62.Fi; 42.60.-v |
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