Mid-infrared laser spectroscopic determination of isotope ratios of N2O at trace levels using wavelength modulation and balanced path length detection
We present a new mid-infrared laser spectrometer for high-precision measurements of isotopic ratios of molecules at ppm concentrations. Results are discussed for nitrous oxide (N2O), where a precision of 3‰ for a single measurement and a reproducibility of 6‰ have been achieved for a concentration of 825 ppm. The room-temperature laser source employed is based on difference-frequency generation delivering a continuous-wave power up to 23 μW at wavelengths between 4.3 μm and 4.7 μm and a line width of 1 MHz. Two different measurement methods are compared; wavelength modulation with first-harmonic detection and direct absorption spectroscopy by recording the spectrum with a data-acquisition card. Two different detection schemes were employed; either all isotopomers were measured using the long path (36 m) of the multipass cell or a balanced path length detection scheme was used, where the main isotope was measured with a beam along a shorter path (40 cm) in the multipass cell. A single-pass reference cell was designed, offering two different path lengths for balanced path length detection. All combinations of measurement methods and detection schemes were tested regarding precision of a single measurement and long-term stability. The advantages and disadvantages of various measurement approaches are discussed.
KeywordsAbsorption Line Quantum Cascade Laser Wavelength Modulation External Cavity Diode Laser Path Detection
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- 1.F.K. Tittel, A.A. Kosterev (guest eds.), Appl. Phys. B 85, 171 (2006)Google Scholar
- 2.D. Yakir, L.S.L. Sternberg, Oecologia (Berlin) 123, 297 (2000)Google Scholar
- 5.F.K. Tittel, D. Weidmann, C. Oppenheimer, L. Gianfrani, Opt. Photon. News 17, 24 (2006)Google Scholar
- 6.A. Amann, D. Smith (eds.), Breath Analysis for Clinical Diagnosis and Therapeutic Monitoring (World Scientific, Singapore, 2005)Google Scholar
- 9.T. Röckmann, J. Kaiser, C.A.M. Brenninkmeijer, W. Brand, Rapid Commun. Mass Spectrom. 17, 1897 (2003)Google Scholar
- 10.D.R. Bowling, P.P. Tans, K.M. Russel, Global Change Biol. 7, 127 (2001)Google Scholar
- 17.W.M. White, Geochemistry (John-Hopkins University Press, Cornell, 1997), Online Textbook, Chapt. 9 [www.geo.cornell.edu/geology/classes/geo455/Chapters.html]Google Scholar
- 19.I.T. Sorokina, K.L. Vodopyanov (eds.), Solid-State Mid-Infrared Laser Sources (Top. Appl. Phys. 89) (Springer, Berlin Heidelberg, 2003)Google Scholar
- 20.J. Faist, Opt. Photon. News 17, 32 (2006)Google Scholar
- 21.H. Waechter, M.W. Sigrist, Mid-infrared coherent sources and applications, in Mathematics, Physics and Chemistry (Nato Sci. Ser. II), ed. by M. Ebrahimzadeh, I.T. Sorokina (Springer, Berlin Heidelberg, 2006)Google Scholar
- 25.T.B. Chu, M. Broyer, J. Phys. France 45, 1599 (1984)Google Scholar
- 27.L.S. Rothman, D. Jacquemart, A. Barbe, D.C. Benner, M. Birk, L.R. Brown, M.R. Carleer, C. Chackerian Jr., K. Chance, L.H. Coudert, V. Dana, V.M. Devi, J.-M. Flaud, R.R. Gamache, A. Goldman, J.-M. Hartmann, K.W. Jucks, A.G. Macki, J.-Y. Mandin, S.T. Massie, J. Orphal, A. Perrin, C.P. Rinsland, M.A.H. Smith, R.N. Tolchenov, R.A. Toth, J. Vander Auwera, P. Varanasi, G. Wagner, J. Quantum Spectrosc. Radiat. Transf. 96, 139 (2005)Google Scholar