A method for measuring gas absorption coefficient based on cavity ring-down technique
A technology of gas absorption and measurement method, applied in the field of measurement, can solve problems such as the relationship between difficult wavelength and ring-down time, limit the wavelength scanning rate, etc., and achieve the effect of reducing random jitter
Active Publication Date: 2021-02-02
TSINGHUA UNIV
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Problems solved by technology
But there are still two problems to be solved here: First, the typical measurement rate of the wavelength meter is 1-10Hz, and the measurement accuracy is 0.001cm -1 , so the maximum wavelength scanning rate must not exceed the measurement rate of the wavelength meter, thus limiting the wavelength scanning rate; second, if the wavelength meter is not used, it is difficult to directly obtain the corresponding relationship between wavelength and ring-down time
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[0051] 1) with CO 2 with N 2 Taking mixed gas as an example, the absorption spectrum line is selected from the HITRAN spectral database, and its center frequency ν 0 6526.374cm -1 , the spectral line intensity is 8×10 -25 cm -1 / (molec·cm -2 ); the temperature of the mixed gas is 23°C, the pressure is 20kPa, CO 2 Concentration 1%;
[0052] 2) With the tunable semiconductor laser 1 as the light source, when the laser frequency is fixed, the laser beam output by the tunable semiconductor laser 1 passes through the optical isolator 2, the acousto-optic modulator 3, and the optical collimator 5 in sequence, and optical fibers are used between the devices 4 connections, the light beam reaches the first plano-concave reflector 6 after being collimated, passes through the ring-down cavity 7, the second plano-concave reflector 8, and then focuses on the photodetector 13 through the convex lens 12; the signal analysis of the photodetector 13 There are two paths, one path is coll...
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A measurement method of gas absorption coefficient based on cavity ring-down technology, which uses scanning laser frequency to obtain periodically changing ring-down time, and then performs fast Fourier transform on it, and selects the Fourier transform of characteristic frequency The ring-down time can be reconstructed by substituting it into the Fourier series; then the interferometer is used to measure the laser frequency, and the relationship between the ring-down time and the laser frequency is re-established, and then the gas absorption coefficient is obtained. The present invention can selectively eliminate various inherent frequency noises and restore the gas absorption coefficient with a higher signal-to-noise ratio; and the interferometer can measure the laser wavelength only once, and is not limited by the measurement accuracy and measurement speed of the wavelength meter; The laser working in scanning mode does not need a high-precision laser controller, which reduces the influence of random jitter of the laser wavelength.
Description
technical field [0001] The invention relates to a method for measuring gas absorption coefficient based on cavity ring-down technology, which is suitable for measuring gas temperature, pressure, concentration and spectral parameters, and belongs to the field of measurement technology. Background technique [0002] The gas absorption coefficient can determine the temperature, pressure, concentration and many spectral parameters of the gas. Cavity ring-down spectroscopy (CRDS) has been proven to be an accurate method to characterize the gas absorption coefficient and a promising method to achieve precise measurement of spectral parameters. One of its advantages is that the equivalent optical path of CRDS can easily reach several kilometers or even tens of kilometers, so the measured spectrum has a high signal-to-noise ratio. Another advantage is that the cavity ring-down spectroscopy (Continuous wave CRDS, CW-CRDS for short) using a continuous wave laser with a narrow linewid...
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IPC IPC(8): G01N21/39G01N21/45
CPCG01N21/39G01N21/45G01N2021/391G01N2021/451
Inventor 彭志敏丁艳军王振
Owner TSINGHUA UNIV