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Proceedings Paper

Investigation of the strengths of vapor rotational absorption lines with different humidity by far infrared absorption spectra
Author(s): Jin Ge; Reng Wang; Su-hong Hu; Ning Dai; Dong Li; Hong Ma; Guo-hong Ma
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Paper Abstract

Terahertz Time Domain Spectroscopy (TDS) provides a new way presenting the 'fingerprint' vibrational or rotational absorption spectra of a lot of molecules. For some molecules, their pure rotational spectra within far infrared wavelength range are much easier to be recognized and discriminated than their vibrational spectra in middle infrared. Especially, vapor molecules have obvious absorption lines in the THz range since it has permanent dipole moment while N2, O2 ,CO2 have none permanent dipole moment. So it is possible to detect the vapor content in atmosphere and study dynamics process with terahertz TDS. We measure the vapor's absorption lines in the range of 0.3-2.0THz at different humidity from 10% to 85% at room temperature. The strengths of the vapor absorption lines within this frequency range have been quantitative measured and the absorption coefficients of these absorption lines at different humidity have been calculated. In addition, the THz absorption spectrum has a frequency resolution of 0.004THz so that the locations of most absorption lines can be defined properly and different absorption lines can be distinguished. Seventeen different lines have been identified consistent with previous work. But it is found that the changes of the lines' intensities with humidity do not obey the same trend. Especially, the absorption coefficients of two lines located at 1.6625THz and 1.6735THz have apparently different behavior when the humidity increases. This phenomenon may be due to the interaction between the vapor molecules. Nevertheless, the ratio of the absorptance of these lines can be used in humidity identification for remote sensing.

Paper Details

Date Published: 4 August 2009
PDF: 11 pages
Proc. SPIE 7385, International Symposium on Photoelectronic Detection and Imaging 2009: Terahertz and High Energy Radiation Detection Technologies and Applications, 73851L (4 August 2009); doi: 10.1117/12.835235
Show Author Affiliations
Jin Ge, Shanghai Institute of Technical Physics (China)
Reng Wang, Shanghai Institute of Technical Physics (China)
Su-hong Hu, Shanghai Institute of Technical Physics (China)
Ning Dai, Shanghai Institute of Technical Physics (China)
Dong Li, Shanghai Univ. (China)
Hong Ma, Shanghai Univ. (China)
Guo-hong Ma, Shanghai Univ. (China)

Published in SPIE Proceedings Vol. 7385:
International Symposium on Photoelectronic Detection and Imaging 2009: Terahertz and High Energy Radiation Detection Technologies and Applications
X.-C. Zhang; James M. Ryan; Cun-lin Zhang; Chuan-xiang Tang, Editor(s)

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