Quantitative analysis of ammonia by THz time-domain spectroscopy

Haibo Liu; Yunqing Chen; Tao Yuan; Fatemah Al-Douseri; Jingzhou Xu; Xi-Cheng Zhang

doi:10.1117/12.518609

27 February 2004 Quantitative analysis of ammonia by THz time-domain spectroscopy

Haibo Liu, Yunqing Chen, Tao Yuan, Fatemah Al-Douseri, Jingzhou Xu, Xi-Cheng Zhang

Author Affiliations +

Proceedings Volume 5268, Chemical and Biological Standoff Detection; (2004) https://doi.org/10.1117/12.518609
Event: Optical Technologies for Industrial, Environmental, and Biological Sensing, 2003, Providence, RI, United States

Abstract

Gas sensing and identification in far infrared or THz band is useful because many polar molecules have unique spectral fingerprints in this range, which are from the rotational transitions of the molecules. We have investigated the potential of THz time-domain spectroscopy (THz TDS) as a quantitative analysis technique for gas sensing. Ammonia vapor has been chosen as a sample gas. The absorption cross section at 0.572 THz of ammonia in the pressure range of 0.2-20 Torr was extracted to be (5.7±0.3)×10^-20 cm²/molecule. In addition, a pressure calibration curve based on pure ammonia measurements was obtained. Using this calibration curve, we made quantitative analysis on the mixture of ammonia and air at 100 Torr. The result shows that THz TDS is an appropriate technique for quantitative analysis of polar gas and gas mixture. We measured the THz spectra of ammonia at different partial pressures in ~590 Torr nitrogen (78% nitrogen in atmosphere), and obtained a pressure calibration curve. THz spectra of ammonia at different partial pressures in 760 Torr atmosphere were measured. Based on the principle of differential optical absorption spectroscopy (DOAS) and the pressure calibration curve got in ~590 Torr nitrogen, we obtained the ammonia partial pressures. The result is compared with the value measured by vacuum gauge and the maximum error is 30%. This indicates that THz TDS based on principle of DOAS is an applicable quantitative technique for sensing ammonia or other polar gases in atmosphere.

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Haibo Liu, Haibo Liu, Yunqing Chen, Yunqing Chen, Tao Yuan, Tao Yuan, Fatemah Al-Douseri, Fatemah Al-Douseri, Jingzhou Xu, Jingzhou Xu, Xi-Cheng Zhang, Xi-Cheng Zhang, } "Quantitative analysis of ammonia by THz time-domain spectroscopy", Proc. SPIE 5268, Chemical and Biological Standoff Detection, (27 February 2004); doi: 10.1117/12.518609; https://doi.org/10.1117/12.518609

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