Gas Detection And Spectral Analysis Of Tunable Diode Laser Absorption Spectroscopy In The Mid-infrared Band

In the field of gas detection,infrared spectral analysis technology has characteristics of fast detection speed,high sensitivity,good repeatability,convenient operation,small amount of sample,instrument has the advantages of simple structure and so on,so the infrared spectral analysis technology has become an important tool for gas detection.The mid infrared spectral band(2.5-25 ?m)contains a "fingerprint" interval,which has a very rich molecular absorption characteristics.Therefore,it is very advantageous to the spectral measurement.However,most of the components have continuous absorption lines in the mid infrared region,which makes it difficult to analyze and detect the mixture.Aiming at the above problems,this paper proposes a component identification method and a quantitative detection method for the tunable laser absorption spectrum in the mid infrared band.The method based on second order derivative spectrum for the original absorption line was used to quantitative detection.The background and noise interference were removed in second order derivative spectrum,and the aliasing absorption peaks were distinguished to a certain extent.In the process of obtaining second order derivative line,the Savitzky-Golay filter was used for smoothing filtering the spectrum.The optimal filter parameters were selected according to the spectral line frequency characteristics,which makes up the lack of the standardized methods in filtering parameters selecting.The wavelet analysis method with appropriate wavelet basis and scale resolution is used to make the time-frequency analysis of the derivative spectrum to obtain the two dimensional time-frequency characteristics matrix.The correlation analysis in both time and frequency dimensions to the time-frequency characteristics matrix of different components and mixtures is researched to realize the component identification in combination with the morphological characteristics of the derivative spectral line.Based on the spectral data and the measured data,the algorithm is validated.The characteristic absorption windows in term of the absorption distribution of corresponding components were applied to both original absorption line and second order derivative spectrum.The characteristic absorption region of more importance in the concentration calculation was extracted,so as to eliminate the interference of background,noise and other components in the non absorption region.The full field fitting method is used to realize quantitative detection.In this paper,the experimental data of a mixture of air and methyl mercaptan is taken as an example to component identification and concentration calculation of tunable laser absorption spectroscopy in the mid infrared band.The experimental results show that the spectral line analysis method proposed in this paper can effectively identify the target components from the mixed spectral lines,and quantitatively analyze the target gas,and the relative error is less than 5%.The research provides a method and technical route for simultaneous detection and spectral analysis of multi-component in the mid infrared band.