Ch₄absorption Spectroscopy Based On Near-infrared DFB Laser

With the rapid growth of the global economy,methane(CH₄),as the main component of natural gas,has become one of the important fuels in production and life.However,due to its flammable and explosive characteristics,it seriously threatens production and personal and property safety.In addition,as an important greenhouse gas,methane plays an important role in accelerating climate warming.Therefore,the development of high-sensitivity detection methods and instruments for methane gas has important practical significance.At present,laser absorption spectroscopy is widely used in the field of gas detection due to its advantages of non-contact,fast response and high sensitivity.Direct absorption spectroscopy is a widely used spectroscopy method.Under the known parameters of molecular line strength,temperature,pressure,etc.,combined with Lambert Beer's law,the concentration information of the gas to be measured can be reversed.However,the spectroscopy parameters in the HITRAN database,which absorption spectroscopy generally rely on,are limited,which cannot meet the demand for high-precision concentration measurement in complex environments in practical applications.In this paper,a semiconductor laser working in the near-infrared band is selected as the light source,combined with a self-written multi-spectral fitting program algorithm,and the R₃transition spectroscopy line parameters in the over-frequency 2v₃absorption band of methane at 1.653?m(wavenumber is 6046.9 cm^-1.)are analyzed.In-depth research,the experimental results are compared with the latest version of the spectroscopy database HITRAN16,the line strength,air widening and self-widening coefficients are all in good agreement.Based on this,in view of the significant influence of the water vapor widening effect,and the widening parameters in the existing spectroscopy database are both dry air-induced widening coefficients that cannot meet the actual application needs,the water vapor-induced methane R₃was carried out through a self-built experimental device.Research on the broadening coefficient of the transition spectrum,and compare it with the related results reported in other literature.Within the experimental error range,the results have good reliability,which can provide important spectral parameters for the correction of the high-precision inversion of methane gas concentration algorithm model in high-humidity environments.In addition,this paper combined the three-mirror cavity structure to build an open trace methane gas detection system based on the near-infrared 1.653?m semiconductor laser.Using wavelength modulation spectroscopy technology and correction algorithms based on related spectroscopy principles,real-time measurement of atmospheric methane is achieved under experimental conditions with an effective optical path length of about 36 m.According to the analysis of Allan deviation,the detection sensitivity of the system is 206.2 ppb in the integration time of 2 s.When the integration time is increased to 798 s,the sensitivity of the system is increased to 8.1 ppb.The experimental system can be widely used in industrial gas processing control,atmospheric environment monitoring and other fields.