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 Title: DUAL COMB RAMAN SPECTROSCOPY ON CESIUM HYPERFINE TRANSITIONS-TOWARD A STIMULATE RAMAN SPECTRUM ON CF4 MOLECULE Author(s): Liu, Tze-Wei Contributor(s): Cheng, Wang-Yau; Hsu, Yen-Chu Subject(s): Mini-symposium: High-Precision Spectroscopy Abstract: Raman spectroscopy is an important spectroscopic technique used in chemistry to provide a fingerprint by which molecules can be identified. It helps us to observe vibration- rotation, and other low-frequency modes in a system. Dual comb Raman spectroscopy allows measuring a wide bandwidth with high resolution in microseconds. The stimulate Raman spectroscopy had been performed in early days where the nonlinear conversion efficiency depended on laser peak power. Hence we propose an approach for rapidly resolving the Raman spectroscopy of CF$_{4}$ molecule by two Ti:sapphire comb lasers. Our progress on this proposal will be presented in the conference. First, we have realized a compact dual Ti:sapphire comb laser systemfootnote{ T.-W. Liu, C.-M. Wu, Y.�C. Hsu and W.-Y. Cheng, Appl. Phys. B 117, 699 (2014)} where the dual Ti:sapphire laser system possesses the specification of 1 GHz repetition rate. In our dual comb system, 1 GHz repetition rate, 100 kHz $Delta$f$_{rep}$ and 2.4 THz optical filter are chosen according to the demands of our future works on spectroscopy. Therefore, the maximum mode number within free spectral range is 5*10$^{3}$, and the widest range of dual-comb based spectra in that each spectrum could be uniquely identified is 5 THz. The actual bandwidth is determined by the employed optical filter and is set to be 2.4 THz here, so that the corresponding data acquisition time is 10 $mu$s. Secondly, since the identification of the tremendous spectral lines of CF$_{4}$ molecule relies on a stable reference and a reliable data-retrieving system, we propose a first-step experiment on atomic system where the direct 6S-8S 822-nm two-photon absorptionfootnote{ P. Fendel, S. D. Bergeson, Th. Udem, and T. W. Hﾊnsch, Opt. Lett. 32, 701 (2007)} and 8S-6P$_{3/2}$ (794 nm) enhanced stimulate Raman would be realized directly by using Ti:sapphire laser. We have successfully performed direct comb laser two-photon spectroscopy for both with and without middle-level enhanced. For the level enhanced two-photon spectrum, our experimental setup achieves Doppler-free spectrum and a record narrow linewidth (1 MHz). Issue Date: 23-Jun-15 Publisher: International Symposium on Molecular Spectroscopy Citation Info: ACS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/79303 Date Available in IDEALS: 2016-01-05
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