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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 Type: Text Language: En URI: http://hdl.handle.net/2142/91439 Rights Information: Copyright 2016 by the authors Date Available in IDEALS: 2016-08-22
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