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Title:Sub-doppler Double-resonance Spectroscopy Of Methane Using A Frequency Comb Probe
Author(s):Lehmann, Kevin
Contributor(s):Soboń, Grzegorz; Rutkowski, Lucile; Foltynowicz, Aleksandra; Axner, Ove; Johanssson, Alexandra C; Silander, Isak; Silva de Oliveira, Vinicius
Subject(s):Small molecules
Abstract:Methane is the first organic molecule detected in hot-Jupiter exoplanets [1] and the observed spectra carry information about the atmospheric conditions, the photochemistry, and planetary formation. To extract this information, we need accurate theoretical models of the spectra verified by high-precision laboratory measurements. However, the energy level structure of highly excited CH$_4$ is poorly understood; there exist limited line-by-line assignments of laboratory spectra above the Icosad polyad (~6,000 \wn). We performed double-resonance spectroscopy using a 3.3 $\mu$m continuous wave pump and 1.67 $\mu$m frequency comb probe to measure sub-Doppler transitions in the 3$\nu$$_{3}$ $\leftarrow$ $\nu$$_{3}$ range (up to 9000 \wn) [2-3]. We detected 36 (J’=0-2) transitions with 1.7 MHz frequency accuracy, limited by the stability of the pump. We assigned the transitions using the intensity ratios measured with parallel and perpendicular pump-probe polarizations, and by comparison of transition frequencies and intensities to predictions from the TheoReTS database [4]. Recently, we implemented an enhancement cavity for the comb probe and improved the absorption sensitivity by two orders of magnitude, allowing detection of a wider range of transitions with better signal-to-noise ratio. Our work is the first measurement of sub-Doppler molecular response using a frequency comb and the first verification of the accuracy of the theoretical prediction that start from highly vibrationally excited methane states. [1] M. R. Swain, G. Vasisht, and G. Tinetti, Nature 452, 329 (2008). [2] A. Foltynowicz et al., Phys. Rev. Lett. 126, 063001 (2021). [3] A. Foltynowicz et al., Phys. Rev. A 103, 022810 (2021) [4] M. Rey, A. V. Nikitin, Y. L. Babikov, and V. G. Tyuterev, J. Mol. Spectrosc. 327, 138 (2016).
Issue Date:2021-06-25
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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