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Applied Optics

Applied Optics


  • Vol. 22, Iss. 23 — Dec. 1, 1983
  • pp: 3701–3710

Water-vapor continuum CO2 laser absorption spectra between 27°C and −10°C

Gary L. Loper, Maureen A. O'Neill, and Jerry A. Gelbwachs  »View Author Affiliations

Applied Optics, Vol. 22, Issue 23, pp. 3701-3710 (1983)

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Water continuum CO2 laser absorption spectra are reported for temperatures between 27 and −10°C. The continuum is found to possess a negative temperature coefficient. The results obtained suggest that the magnitude of this temperature coefficient increases with increasing water pressure and decreasing temperature. The temperature coefficients between 27 and 10°C for air mixtures containing 3.0- and 7.5-Torr water vapor are −2.0 ± 0.4 and −2.9 ± 0.5%/°C, respectively. For mixtures with 3.0-Torr water the 10–0°C temperature coefficient is −7.7 ± 0.2%/°C. The temperature and water pressure dependencies observed for the continuum suggest that while both collisional broadening and water dimer mechanisms contribute to the continuum, the dimer mechanism is more important over this temperature range.

© 1983 Optical Society of America

Original Manuscript: July 25, 1983
Published: December 1, 1983

Gary L. Loper, Maureen A. O'Neill, and Jerry A. Gelbwachs, "Water-vapor continuum CO2 laser absorption spectra between 27°C and −10°C," Appl. Opt. 22, 3701-3710 (1983)

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  27. The so-called self-broadening coefficient Cs(λ,T) plotted vs temperature in Fig. 8 is most often defined in the literature through the relationabs(λ,T)=Cs(λ,T)wH2O[pH2O+γ(λ,T)(P−pH2O)].Here abs(λ,T) is the water continuum absorption coefficient at a particular wavelength and temperature, wH2O is the density of water vapor in units of molecules/cm3, pH2O is the water partial pressure, P is the total pressure in units of atmospheres, and γ(λ,T) = Cf(λ,T)/Cs(λ,T) is the foreign-broadening to self-broadening coefficient ratio.
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  31. For most atmospheric conditions, the magnitude of the continuum absorption is primarily governed by its water pressure quadratic component. From the linear and quadratic coefficients in Table II, it is observed that the quadratic water pressure component contributes predominantly to the total water absorption coefficient at 27 and 10°C for water pressures greater than ∼3 and 2 Torr, respectively. For lower temperatures, the quadratic component would be the major contributor to the continuum at even lower pressures.
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