Measurements of near-IR water vapor absorption at high pressure and temperature

• Published in: Applied physics. B, Lasers and optics Vol. 87; no. 1; pp. 169 - 178
• Main Authors: RIEKER, G. B, LIU, X, LI, H, JEFFRIES, J. B, HANSON, R. K
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.03.2007
• Subjects: Absorption spectra; Approximation; Biological and medical applications; Breakdown; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Laser spectroscopy; Mathematical analysis; Mathematical models; Optics; Physics; Spectra; Water vapor; Near infrared spectrometry; Semiconductor lasers; Line shape; Second harmonic; Laser spectroscopy; Steam; Measuring methods; High temperature; Absorption spectra; Modulation spectroscopy; Laser diodes; High pressure
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-006-2523-4

Tunable diode lasers (TDLs) are used to measure high resolution (0.1 cm-1), near-infrared (NIR) water vapor absorption spectra at 700 K and pressures up to 30 atm within a high-pressure and -temperature optical cell in a high-uniformity tube furnace. Both direct absorption and wavelength modulation with second harmonic detection (WMS-2f) spectra are obtained for 6 cm-1 regions near 7204 cm-1 and 7435 cm-1. Direct absorption measurements at 700 K and 10 atm are compared with simulations using spectral parameters from HITRAN and a hybrid database combining HITRAN with measured spectral constants for transitions in the two target spectral regions. The hybrid database reduces RMS error between the simulation and the measurements by 45% for the 7204 cm-1 region and 28% for the 7435 cm-1 region. At pressures above 10 atm, the breakdown of the impact approximation inherent to the Lorentzian line shape model becomes apparent in the direct absorption spectra, and measured results are in agreement with model results and trends at elevated temperatures reported in the literature. The wavelength-modulation spectra are shown to be less affected by the breakdown of the impact approximation and measurements agree well with the hybrid database predictions to higher pressures (30 atm).