Design And Implementation Of Tunable Diode Laser Absorption Spectroscopy System For Trace Gas Detection

With the development of the technology and times,the gas detection technology has been widely used in various industries,such as natural gas,coal,metallurgy,power,medical,environmental protection and so on.Gas detection technology has gradually become an important factor to ensure the sustainable development of society and human healthy.In industry production and daily life,the gas detection technology constantly put forward higher requirements,not only the detection process is simple,easy to operate but also has fast detection speed and high accuracy.These requirements can be met by using optical detection technology.Compared with electrochemical gas sensing technology,laser spectroscopy technology has great advantages in specificity,sensitivity and response speed.The commonly used non dispersive infrared spectroscopy（NDIR）is easy to be affected by the fluctuation of light source intensity and the background drift;cavity ring down spectroscopy（CRDS）has very high requirements for ring down cavity and light source linewidth,so it is difficult to develop a compact and low-cost portable system.Tunable diode laser absorption spectroscopy（TDLAS）has the advantages of high resolution,high selectivity,high sensitivity,fast response,wide measurement range,high stability and simple to use.In this paper,the characteristics of several types of optical gas cell are analyzed by investigating the research status of long optical path gas cell at home and abroad.Based on the theory,the gas pool was simulated by the Trace Pro optical simulation software,and a series of theoretical data were obtained.By means of tunable diode laser absorption spectroscopy,the laser wavelength emitted by the diode is scanned through the peak absorption spectrum of the gas molecule to be measured,thus the relatively complete absorption spectrum can be obtained,and the gas can be analyzed accurately.Finally,the second harmonic signals of different concentrations of CO₂ are measured,and a good linear relationship between the concentration and the 2f signal was obtained.The system can be used for the measurement of environmental gases and human respiratory markers.By changing the wavelength of laser source,other trace gases can also be measured.