| Laser absorption spectroscopy has greatly improved the spectral resolution and detection sensitivity,due to the continuous improvement of the performance of the tunable semiconductor laser and detector.With the continuous emergence of new gas detection methods,the engineering and practicability of measuring instruments based on laser absorption spectroscopy have been built,and has been widely used in atmospheric environmental monitoring,plant process control and exhaust emissions,gas stable isotope detection and so on.In view of the requirements of miniaturization and high precision of trace gas measuring instruments,the research and application of long path laser absorption spectroscopy technology are carried out in this paper.Firstly,a calibration free wavelength modulation absorption spectrum algorithm is developed,a set of TDALS gas measurement system is established,and the C2H2 gas is detected without calibration.Secondly,a pollution prevention flat convex mirror multipass cell is designed,a set of high temperature NH3 measurement system is set up to detect the corrosion NH3.Finally,a set of isotope detection prototype to detect CO2 and CH4 isotopes is built using the independent design of the off-axis cavity enhancement system and the laser controller circuit made in the laboratory.The research results and innovation of the paper mainly include:1.A calibration free wavelength modulation absorption spectroscopy algorithm has been developed and a set of TDLAS gas detection system has been built,using a DFB diode laser with a central wavelength of 1.53 ?m and a cylindrical mirror optical multipass cell with an effective optical path of 10.5 m,the C2H2 gas is detected by the method of calibration free wavelength modulation absorption spectroscopy.The measurement error of its concentration is less than 5%,compared with the traditional wavelength modulation absorption spectroscopy,the accuracy of the method is increased by 3.5 times,the system is analyzed by Allan variance,the minimum detectable concentration of the system reaches 0.127 ppm at the average time of 1 s,when the average time of the system reaches 118s,the detection limit can reach 0.031 ppm.The calibration free wavelength modulation absorption spectrum measurement system has the advantages of high sensitivity,high resolution,fast response and calibration free,has wide application in the field of gas trace detection,especially in the overlapping of absorption lines and relatively harsh environment.2.A set of pollution prevention flat convex mirror multipass cell is designed,and a TDLAS high temperature real-time NH3 gas measuring system is established.a DFB diode laser with a central wavelength of 1.531 ?m was used for the detection of NH3gas at a high temperature of 180 degrees.The accuracy of the wavelength modulation method is 2 times that of the direct absorption method,by the Allan analysis of the system,the minimum detectable concentration of the system reaches 0.33 ppm at the average time of 1 s,and the detection limit can reach 0.11 ppm when the average time of the system reaches 200 s.A new type of pollution prevention flat convex mirror multipass cell has the characteristics of compact structure,can not only prevent the corrosion of the lens,but also increase the absorption of the optical path and improve the detection sensitivity of the system,has been widely applied in trace gas detection,especially in the field of detection of corrosive and adsorptive trace gases.3.A set of real-time isotope measurement prototype is built based on independently designed off-axis cavity enhancement absorption spectroscopy device and the DFB laser controller and photoelectric detector circuit made in the laboratory,the CO2 and CH4 gas isotopes were detected by direct absorption spectroscopy using a DFB diode laser with a central wavelength of 1.605 ?m and 1.658 ?m respectively.The experimental results show that,for the measurement of CO2 isotope abundance,when the sampling time is 1 s,the accuracy of ? value is 5.37 ‰,and the average time is 343 s,the accuracy of 8 value can reach 0.21 ‰,1 s sampling period,the accuracy of the original data Kalman filtered delta value is 1.05‰.Measurement of CH4 isotopic abundance,when the sampling time is 1 s,the accuracy of 8 value is 8.62 ‰,and the average time is 343 s,the accuracy of 8 value can reach 1.08 ‰,1 s sampling period,the accuracy of the original data Kalman filtered delta value is 2.85 ‰.The off-axis cavity enhanced measurement device has the advantages of simple structure,high sensitivity,fast response and long optical path in small volume,Kalman filtering can greatly improve the measurement accuracy of the detection system in the same sampling time,has been widely applied in the field of trace gas and isotope detection. |
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