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Title:High-precision Mid-infrared Spectroscopy With A Widely Tuneable Si-traceable Frequency-comb-stabilised Qcl
Author(s):Cahuzac, Nicolas
Contributor(s):Darquie, Benoit; Amy-Klein, Anne; Le Targat, Rodolphe; Pottie, Paul-Eric; Le Coq, Yann; Abgrall, Michel; Xu, Dan; Lopez, Olivier; Cantin, Etienne; Santagata, Rosa; Tran, Dang Bao An; Manceau, Mathieu
Subject(s):Instrument/Technique Demonstration
Abstract:There is an increasing demand for precise molecular spectroscopy, in particular in the mid-IR fingerprint window, whether it be for modelling our atmosphere, interpreting astrophysical spectra or testing fundamental physics. Here, we present a new technology for ultra-high-resolution vibrational spectroscopy using quantum cascade lasers (QCLs) traceable to primary standards \footnote{Santagata, R., et al., Optica 6, no. 4 (2019): 411-423.}. Using an optical frequency comb, a $10$ $\mu$m QCL is stabilized at the sub-Hz level to an ultra-stable near infrared reference signal operated at the French metrology institute. This signal is calibrated there to some of the best atomic clocks and transferred through a noise-compensated 43-km long fiber cable. This results in a record ~0.1 Hz QCL linewidth. We have also developed a method to continuously scan the stabilized QCL over 1.5 GHz at the precision of the frequency reference. We have used the apparatus to carry out saturated absorption spectroscopy in a compact multipass cell. We have measured absolute frequencies (as well as frequency shifts and pressure broadening) of osmium tetroxyde, methanol, ammonia and trioxane, with record uncertainties, from 10 Hz to 10 kHz (depending on the species and the details of the apparatus). We were able to resolve yet unreported subtle structures in methanol (doublets and triplets induced by the combined effects of tunnelling and asymmetry). We have recently added to our spectrometer a 3 meter-long Fabry-Perot resonator to perform cavity enhanced measurements in order to improve our resolution and extend saturated absorption spectroscopy to more complex molecules. First results will be presented.
Issue Date:2021-06-22
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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