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.