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|Author(s):||Keith A. Gillis; Daniel K. Havey; Joseph T. Hodges;|
|Title:||Standard Photoacoustic Spectrometer: Model and Validation using O2 A-Band Spectra|
|Published:||June 30, 2010|
|Abstract:||We model and measure the absolute response of an intensity-modulated photoacoustic spectrometer comprising a 10 cm long resonator and having a Q-factor of approximately 30. We present a detailed theoretical analysis of the system and predict its response as a function of gas properties, resonance frequency, and sample energy transfer relaxation rates. We use a low-power continuous wave laser to probe O2 A-band absorption transitions using atmospheric, humidified air as the sample gas to calibrate the system. This approach provides a convenient and well-characterized method for calibrating the absolute response of the system provided that water-vapor-mediated relaxation effects are properly taken into account. We show that for photoacoustic spectroscopy (PAS) of the O2 A-band, the maximum conversion efficiency of absorbed photon energy to acoustic energy is approximately 40% and is limited by finite collision-induced relaxation rates between the two lowest-lying excited electronic states of O2. The technique also shows great potential for high-resolution line shape measurements. We directly compare calculated and experimental values for the PAS system response and show that they differ by about 1%.|
|Citation:||Review of Scientific Instruments|
|Pages:||pp. 064902-1 - 064902-13|
|Keywords:||A-band, aerosol, calibration, line shape, molecular relaxation, oxygen, photoacoustic spectrometry, water|
|Research Areas:||Measurement Standards, Climate Science Measurements, Gas Metrology, Standards, Chemical Engineering & Processing, Chemistry, Metrology, Aerosol/Particulate Measurements and Standards, Spectroscopy|
|PDF version:||Click here to retrieve PDF version of paper (608KB)|