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Title:Doppler broadening thermometry based on cavity ring-down spectroscopy
Author(s):Hu, Shui-Ming
Contributor(s):Liu, An-Wen; Kang, Peng; Tan, Yan; Tao, Lei-Gang; Cheng, Cunfeng; Sun, Yu Robert; Wang, Jin
Subject(s):Fundamental interest
Abstract:A Doppler broadening thermometry (DBT) instrument is implemented based on a laser-locked cavity ring-down spectrometer.~[1,2] It can be used to determine the Boltzmann constant by measuring the Doppler width of a molecular ro-vibrational transition in the near infrared. Compared with conventional direct absorption methods, the high-sensitivity of CRDS allows to reach satisfied precision at lower sample pressures, which reduces the influence due to collisions. By measuring the ro-vibrational transition of C$_2$H$_2$ at 787~nm, we demonstrate a statistical uncertainty of 6~ppm (part per million) in the determined linewidth by several hours' measurement at a sample pressure of 1.5~Pa.~[3] However, the complicity in the spectrum of a polyatomic molecule induces potential systematic influence on the line profile due to nearby ``hidden'' lines from weak bands or minor isotopologues. Recently, the instrument has been upgraded in both sensitivity and frequency accuracy. A narrow-band fiber laser frequency-locked to a frequency comb is applied, and overtone transitions at 1.56~$\mu$m of the $^{12}$C$^{16}$O molecule are used in the CRDS-DBT measurements. The simplicity of the spectrum of the diatomic CO molecule eliminates the potential influence from ``hidden'' lines. Our preliminary measurements and analysis show that it is feasible to pursue a DBT measurement toward the 1~ppm precision. \begin{thebibliography}{3}% \bibitem {Pan2011RSI_LL_CRDS}% H. Pan, et al., Rev. Sci. Instrum. \textbf{82}, 103110 (2011) \bibitem {Sun2011OE}% Y.~R. Sun, et al., Opt. Expr., \textbf{19}, 19993 (2011) \bibitem {Cheng2015Met_DBT}% C.-F. Cheng, et al., Metrologia, \textbf{52}, S385 (2015) \end{thebibliography}%
Issue Date:2016-06-21
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper/Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2016-08-22

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