Measurements of high-pressure CO2 absorption near 2.0 μm and implications on tunable diode laser sensor design
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- Rieker, G.B., Jeffries, J.B. & Hanson, R.K. Appl. Phys. B (2009) 94: 51. doi:10.1007/s00340-008-3280-3
A tunable diode laser (TDL) is used to measure the absorption spectra of the R46 through R54 transitions of the 20012←00001 band of CO2 near 2.0 μm (5000 cm−1) at room temperature and pressures to 10 atm (densities to 9.2 amagat). Spectra are recorded using direct absorption spectroscopy and wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) in a mixture containing 11% CO2 in air. The direct absorption spectra are influenced by non-Lorentzian effects including finite-duration collisions which perturb far-wing absorption, and an empirical χ-function correction to the Voigt line shape is shown to greatly reduce error in the spectral model. WMS-2f spectra are shown to be at least a factor of four less-influenced by non-Lorentzian effects in this region, making this approach more resistant to errors in the far-wing line shape model and allowing a comparison between the spectral parameters of HITRAN and a new database which includes pressure-induced shift coefficients. The implications of these measurements on practical, high-pressure CO2 sensor design are discussed.