Research on Wavelength Shift Correction Algorithm for Tunable Laser Absorption Spectrum
TANG Qi-xing1, 2, ZHANG Yu-jun1*, CHEN Dong1, 3, ZHANG Kai1, 2, HE Ying1, YOU Kun1, LIU Guo-hua1, 2, LU Yi-bing1, 2, FAN Bo-qiang1, 2, YU Dong-qi1, 2
1. Key Laboratory of Environmental Optics & Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
2. Science Island Branch, University of Science and Technology of China, Hefei 230026, China
3. School of Instrument Science and Optoelectronic Engineering, Hefei University of Technology, Hefei 230009, China
Abstract：Tunable semiconductor laser is featured by narrow bandwidth, fast wavelength scanning, and room temperature working temperature, etc. The laser absorption spectroscopy gas measurement system based on tunable diode laser is widely applied in atmospheric environmental monitoring and on-line industrial production process detection. In the actual measurement system, the center wavelength of the tunable semiconductor laser is affected by temperature and other factors. If the center wavelength is not corrected, the spectral data will be overlapped and the processed spectral line will be widened, which will affect the subsequent spectral line fitting and affect the accuracy of gas concentration inversion. Generally, the reference spectrum absorption line peak-finding method is used to align the offset of the spectral data. However, the accuracy of the peak wavelength in the spectral data is affected the random noise, the background and drift noise. In order to reduce the side effects mentioned above, an improved algorithm of the time domain correlation is proposed. Firstly, the autocorrelation of the spectral signal is carried out to improve the spectral signal-to-noise ratio to a certain extent, then the time-domain cross-correlation processing is applied, which can accurately calculate the laser wavelength offset, reduce the influence of spectral broadening, and improve the concentration inversion accuracy and measurement stability. Experiments have been carried out in the detection experimental system of gas concentration based on laser absorption. Experimental results show that the standard deviation of the original data is 1.482 8 while the standard deviation of data correction is 0.433 9 and 0.293 6, respectively. The corrected standard deviation of improved method of time domain correlation correction is 0.132 5 with the correlation coefficient higher than 0.992. The standard deviation of Euclidean distance is 1.726 4. The system stability evaluation indicates that the modified standard deviation of the wavelength drift correction is up to 0.144 3.
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