To determine the reflectance of the optical resonator lens, an open optical resonant cavity and a long-path absorption reference cell (absorption length has already known) were build up. The measurement is executed with a spectral line of 13146.58cm-1 in the atmospheric environment. By adjusting the resonator cavity length, the integrated absorbance at different cavity lengths is obtained and compared with the integrated absorbance of the long-path absorption cell to obtain the cavity length gain coefficient. The average value of the gain coefficient measured in the experiment is 85.1782, the standard deviation is 0.420123, and the average reflectivity is calculated as 0.988396, the standard deviation is 0.000056324. To determine the accuracy of the reflectance, we adjusted the cavity length to 17cm, and measured the oxygen absorption spectral signal in the atmospheric environment (@288.5K,1atm).The measured integral absorbance A is 0.0574223(S(δ)=0.000436793), the calculated oxygen component concentration X=20.86%, compared with the value measured by the oxygen concentration meter, the error ∆=0.0031%. The experimental results show that this system can effectively carry out calibration work of cavity mirror reflectivity, at the same time, it also proves that the system has the ability to measure weak-oxygen spectrum absorption signals under short-distance conditions.
Based on wavelength modulation spectroscopy and algebraic reconstruction technique, two-dimensional tomography of gas temperature in the range of 400K-1500K and H2O concentration in the range of 0.05-0.20 was realized. From the numerical simulation, the transmitted signals of two lines using wavelength modulation spectroscopy method are simulated, then the integrated areas of the absorption lines are obtained. Using the integrated areas of two lines, the two-dimensional tomographic reconstruction are derived. It is shown that the reconstructed gas temperature and H2O concentration are consistent with the predicted value and the most relative errors are 2.21% and 5.17%.
Integrated cavity output spectroscopy (ICOS) is a technique used for high sensitive measurement of absorption spectra. In this paper,we introduced the principle of ICOS measurement technology. By analyzing the theory of ICOS technology to effectively absorb the increase of optical path length, get the relationship of the specular reflectance and the selection for the length of cavity to the stability of cavity and detection sensitivity in the designing of experimental facility. We introduced the application of ICOS technology in atmospheric monitoring, medical testing, and industrial process and so on, summed up the role of wavelength modulation and off-axis incidence combined with ICOS on noise suppression. We summed up the advantages and disadvantages of ICOS technology in trace gas detection. At the end of the paper, the trend of ICOS technology was analyzed.
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