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 Title: CO2 LINE PARAMETER RETRIEVAL BEYOND THE VOIGT PROFILE USING COMB-BASED FOURIER TRANSFORM SPECTROSCOPY Author(s): Johanssson, Alexandra C. Contributor(s): Foltynowicz, Aleksandra; Maslowski, Piotr; Rutkowski, Lucile; Filipsson, Anna Subject(s): Mini-symposium: Frequency-Comb Spectroscopy Abstract: Mechanical Fourier transform spectrometers (FTS) based on optical frequency combs (OFC) allow precise measurement of comb line intensities when the nominal resolution of the FTS is precisely matched to the repetition rate of the comb\footnote{ Masłowski, P., et al., Phys. Rev. A 93, 021802 (2016).}$^,$\footnote{ Rutkowski, L., et al., J. Quant. Spectrosc. Radiat. Transf. 204, 63-73 (2018).}. Under this condition, the resolution and frequency scale accuracy are given by the narrow comb lines rather than the spectrometer, and the measured spectra are not influenced by the instrumental lineshape. Here we use an FTS based on an Er:fiber frequency comb to perform high-precision direct absorption measurements of the 3$\nu_1$+$\nu_3$ absorption band of pure CO$_2$ at 1.57 $\mu$m. The sample is held inside a multipass cell, and a spectrum of the entire band with signal to noise ratio (SNR) up to 1000 is acquired in $\sim$27 min at one pressure. We retrieve the parameters of individual lines using multiline fitting with the Voigt profile (VP) and the speed-dependent Voigt profile (SDVP), with significantly improved residuals for the SDVP (quality factors close to the SNR for the SDVP). Moreover, the SDVP fits agree with the measured profiles much better than in previous measurements of the same molecular band\footnote{Larcher, G., et al., J. Quant. Spectrosc. Radiat. Transf. 164, 82-88 (2015).}. The transition frequencies have precision much better than those stated in the HITRAN2016 database\footnote{Gordon, I. E., et al., J. Quant. Spectrosc. Radiat. Transf. 203, 3-69 (2017).} and at a similar level as those obtained with continuous wave cavity ring-down spectroscopy\footnote{Long, D.A., et al., J. Quant. Spectrosc. Radiat. Transf. 161, 35-40 (2015).}. Thus comb-based FTS is a perfect tool for spectroscopy of entire absorption bands with precision beyond the Voigt profile and for retrieval of molecular line parameters for improved spectroscopic databases. Issue Date: 06/20/18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/100633 DOI: 10.15278/isms.2018.WG07 Other Identifier(s): WG07 Date Available in IDEALS: 2018-08-172018-12-12
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