Abstract
Combining cavity ring down spectroscopy (CRDS) and wavelength modulated direct absorption spectroscopy (WM-DAS), a wide range and calibration-free gas concentration detection method is established, which has the advantages of high signal-to-noise ratio of CRDS and fast speed and measurable absolute concentration of WM-DAS. The baseline ring down time (<i>τ</i><sub>0</sub>) can be calculated by measuring the absorptivity (WM-DAS) and ring down time (CRDS) at the central frequency of the spectral line, without real-time calibration, which greatly improves the speed of CRDS measurement. The measurement results of different H<sub>2</sub>S concentrations at 6336.617 cm<sup>–1</sup> at room temperature and atmospheric pressure show that the dynamic measurement range of this method can be extended to more than 4 orders of magnitude, the measurement accuracy is improved in comparison with WM-DAS, and the detection limit can reach 1 × 10<sup>–9</sup> in 40 s.
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