Investigation of the strengths of vapor rotational absorption lines with different humidity by far infrared absorption spectra

Jin Ge; Reng Wang; Su-hong Hu; Ning Dai; Dong Li; Hong Ma; Guo-hong Ma

doi:10.1117/12.835235

4 August 2009 Investigation of the strengths of vapor rotational absorption lines with different humidity by far infrared absorption spectra

Jin Ge, Reng Wang, Su-hong Hu, Ning Dai, Dong Li, Hong Ma, Guo-hong Ma

Author Affiliations +

Proceedings Volume 7385, International Symposium on Photoelectronic Detection and Imaging 2009: Terahertz and High Energy Radiation Detection Technologies and Applications; 73851L (2009) https://doi.org/10.1117/12.835235
Event: International Symposium on Photoelectronic Detection and Imaging 2009, 2009, Beijing, China

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.

Citation Download Citation

Jin Ge, Reng Wang, Su-hong Hu, Ning Dai, Dong Li, Hong Ma, and Guo-hong Ma "Investigation of the strengths of vapor rotational absorption lines with different humidity by far infrared absorption spectra", Proc. SPIE 7385, International Symposium on Photoelectronic Detection and Imaging 2009: Terahertz and High Energy Radiation Detection Technologies and Applications, 73851L (4 August 2009); https://doi.org/10.1117/12.835235

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