title: Standard photoacoustic spectrometer: model and validation using O2 A-band spectra.
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 O(2) 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 O(2) 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 O(2). PAS also shows great potential for high-resolution line shape measurements: calculated and experimental values for the PAS system response differ by about 1%.
authors.affiliation: Process Measurements Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA. keith.gillis@nist.gov
authors.forename: K A
authors.initials: KA
authors.lastname: Gillis
authors.forename: D K
authors.initials: DK
authors.lastname: Havey
authors.forename: J T
authors.initials: JT
authors.lastname: Hodges