Research on a method of eliminating the line broadening caused by the wavelength shift based on the first harmonic.

Using laser spectroscopy for gas detection, short-term rapid changes in ambient temperature, system noise, and circuit aging are likely to cause line broadening, which affects the accuracy of gas concentration measurement. Firstly, the correction method of the impact on line broadening is analyzed theoretically. A method is proposed to eliminate the line broadening caused by the wavelength shift based on the first harmonic detection. After removing the background noise and filtering, the standard harmonic fitting and broadening elimination are carried out. Meanwhile, a methane gas detection system is established and experiments are conducted. The experimental results show that after the standard harmonic fitting, the maximum value of the baseline is reduced from 2 to 0.078, and the maximum absolute value of the baseline in the absorption-free region is reduced from 2.07 to 0.072. The standard deviation after the broadening correction is 0.047, and the standard deviation without considering the effect of broadening is 0.203, which proves that the accuracy of trace gas detection is improved and has good engineering practical value.

Laser absorption spectroscopy data processing method based on co-frequency and dual-wavelength and its application.

In the detection process of atmospheric laser absorption spectroscopy in open space, the transmitted beam is inevitably affected by atmospheric turbulence, resulting in superimposed fluctuation noise in the received optical signal. First, the correction method of atmospheric turbulence is theoretically analyzed. In order to reduce the error influence factors and the error transfer coefficient, a new method of spectral data processing based on co-frequency and dual-wave has been proposed. By modifying scintillation noise and background noise, the influence of atmospheric turbulence noise in open space is reduced. An atmospheric detection system in open space based on co-frequency and dual-wave has been established. The experimental results show that the maximum fluctuation of the spectral signal processed by the method of spectrum data processing based on the co-frequency and dual-wave is reduced from 12.854% to 4.635%, and the single-intensity absorbance is fitted by Voigt with its correlation coefficient of 0.9525. The mean of the standard deviation of the algorithm is 0.1370, while the mean value of the standard deviation of the existing algorithm in a short time is 0.6928. And, through the comparative experiment, the standard deviation of the existing data processing techniques of two-wavelength differential absorption is 0.2974, while the standard deviation of the method of spectrum data processing based on the co-frequency and dual-wave is 0.1038. It can be concluded that the co-frequency and dual-wave method can effectively reduce the influence of atmospheric turbulence noise and laser flashing to improve the stability of concentration measurement, which has practical engineering value.