Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation

A photoacoustic sensor has been developed for trace-gas monitoring using a near-infrared semiconductor laser emitting in the 2ν3 band of methane at 1.65 μm. The apparatus was designed for on-line process control in the manufacturing of the novel low-water-peak fibres developed for optical telecommunications. The importance of collisional relaxation processes in the generation of the photoacoustic signal is reported in the particular case of CH4 detection in dry O2 and O2–N2 mixtures. The negative influence of these effects results in a strongly reduced and phase-shifted photoacoustic signal, induced by a fast resonant coupling between the vibrational states of methane and oxygen, associated with the slow relaxation of the excited oxygen molecules. An unusual parabolic response of the sensor with respect to the methane concentration has been observed and is discussed. Finally, the beneficial effect of several species, including water vapour and helium, acting as a catalyst to hasten the relaxation of the CH4–O2 system, is demonstrated.

[1]  J. Henningsen,et al.  Photoacoustic study of kinetic cooling , 1992 .

[2]  Zsolt Bor,et al.  Near-Infrared Diode Laser Based Spectroscopic Detection of Ammonia: A Comparative Study of Photoacoustic and Direct Optical Absorption Methods , 2002, Applied spectroscopy.

[3]  Luc Thévenaz,et al.  Ammonia monitoring at trace level using photoacoustic spectroscopy in industrial and environmental applications. , 2004, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.

[4]  A. Kosterev,et al.  Ammonia detection by use of quartz-enhanced photoacoustic spectroscopy with a near-IR telecommunication diode laser. , 2004, Applied optics.

[5]  S. Schilt,et al.  Wavelength modulation photoacoustic spectroscopy: Theoretical description and experimental results , 2006 .

[6]  C. Boursier,et al.  Rovibrational Energy Transfer in Methane Excited to 2ν3 in CH4−N2 Mixtures from Double-Resonance Measurements , 2001 .

[7]  C. Dewey.  3 – Design of Optoacoustic Systems , 1977 .

[8]  Luc Thévenaz,et al.  Multi-gas sensing based on photoacoustic spectroscopy using tunable laser diodes. , 2004, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.

[9]  Luc Thévenaz,et al.  Application of antimonide diode lasers in photoacoustic spectroscopy. , 2004, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.

[10]  Frank K. Tittel,et al.  Ultrasensitive gas detection by quartz-enhanced photoacoustic spectroscopy in the fundamental molecular absorption bands region , 2005 .

[11]  J. Hackstein,et al.  Intracavity CO laser photoacoustic trace gas detection: cyclic CH(4), H(2)O and CO(2) emission by cockroaches and scarab beetles. , 1996, Applied optics.

[12]  Markus W. Sigrist,et al.  Atmospheric pollution monitoring using CO2‐laser photoacoustic spectroscopy and other techniques , 1990 .

[13]  Luc Thevenaz,et al.  Fibre-coupled photoacoustic sensor for sub-ppm methane monitoring , 2004, European Workshop on Optical Fibre Sensors.

[14]  Z. Bozóki,et al.  External Cavity Diode Laser Based Photoacoustic Detection of CO2 at 1.43 μm: The Effect of Molecular Relaxation , 2003, Applied spectroscopy.

[15]  Markus W. Sigrist,et al.  Trace gas monitoring by laser-photoacoustic spectroscopy , 1995 .

[16]  H. Bass,et al.  Kinetic model for thermal blooming in the atmosphere. , 1973, Applied Optics.

[17]  Kathy Kincade.  CWDM breathes life into metro, access, and enterprise applications , 2003 .

[18]  A. D. Wood,et al.  Effects of 10.6-mu Laser Induced Air Chemistry on the Atmospheric Refractive Index. , 1971, Applied optics.

[19]  C. Camy‐Peyret,et al.  VIBRATIONAL ENERGY TRANSFER IN METHANE EXCITED TO 2NU 3 IN CH4-N2O2 MIXTURES FROM LASER-INDUCED FLUORESCENCE MEASUREMENTS , 1998 .

[20]  D. White,et al.  Oxygen Vibrational Relaxation in O2sHe and O2sAr Mixtures , 1963 .

[21]  C. Boursier,et al.  Rovibrational relaxation of methane in CH4-N2 mixtures: Time-resolved IR-IR double-resonance measurements at 193 K and kinetic modeling , 2003 .

[22]  Michael E. Webber,et al.  Laser-based photoacoustic ammonia sensors for industrial applications , 2002 .

[23]  J. Yardley,et al.  Erratum: Vibration–Vibration and Vibration–Translation Energy Transfer in Methane–Oxygen Mixtures , 1968 .

[24]  R. Rooth,et al.  Photoacoustic measurement of ammonia in the atmosphere: influence of water vapor and carbon dioxide. , 1990, Applied optics.

[25]  D. White.  Vibrational Relaxation of Oxygen by Methane, Acetylene, and Ethylene , 1965 .