| 1. |
- Alwahabi, ZT, et al.
(författare)
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Infrared polarization spectroscopy of CO2 at atmospheric pressure
- 2004
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Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018. ; 233:4-6, s. 373-381
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Tidskriftsartikel (refereegranskat)abstract
- Polarisation spectroscopy (PS) was used to probe CO2 gas concentration in a CO2/N-2 binary mixture at atmospheric pressure and ambient temperature. The CO2 molecules were probed by a direct laser excitation to an overtone and combination vibrational state. The tuneable narrow linewidth infrared laser radiation at 2 mum was obtained by Raman shifting of the output from a single-longitudinal-mode pulsed alexandrite laser-system to the second Stokes component in a H, gas cell. Infrared polarisation spectroscopy (IRPS) and time-resolved infrared laser-induced fluorescence (IRLIF) spectra were collected. A linear dependence of the IRPS signal on the CO2 mole fraction has been found. This indicates that the IRPS signal is only weakly affected by the molecular collisions and that the inter- and intra- molecular energy transfer processes do not strongly influence the molecular alignment at the time scale of the measurements. Thus IRPS holds great potential for quantitative instantaneous gas concentration diagnostics in general. This is especially important for molecules which do not posses an accessible optical transition such as CO, CO2 and N2O. In addition, an accurate experimental method to measure the extinction ratio of the IR polarisers employed in this study has been developed and applied. With its obvious merits as simplicity, easy alignment and high accuracy, the method can be generalized to all spectral regions, different polarisers and high extinction ratios.
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| 2. |
- Li, Zhongshan, et al.
(författare)
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Detection of methane with mid-infrared polarization spectroscopy
- 2004
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 79:2, s. 135-138
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Tidskriftsartikel (refereegranskat)abstract
- We report on the application of polarization spectroscopy in the midinfrared spectral region for the detection of methane by probing its asymmetric ro-vibrational transitions. Tunable infrared laser radiation, near 3.4 mum, was obtained from difference-frequency generation in a LiNbO3 crystal. Infrared polarization spectroscopy (IRPS) spectra of the P, Q and R branches of the nu(3) band, recorded with both linearly and circularly polarized pump beams, are presented. The experiments were performed in an atmospheric pressure gas jet with methane diluted with Ar. An IRPS spectrum with signal-to-noise ratio better than 10(4) was observed. The dependence of the IRPS signal intensity on the methane mole fraction and on the pumping laser power density was investigated.
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