Study On Trace Gas Concentration By Cavity Enhanced Absorption Spectroscopy

In recent years,the outbreak of environmental pollution has aroused people's attention to environmental protection.A variety of absorption spectroscopy techniques have been developed and used to detect the concentration of air pollutants.However,the experimental device of cavity enhanced absorption spectroscopy technology is simple,low cost,detection sensitivity and robustness.Based on these advantages of cavity enhanced absorption spectroscopy,it was used to detect NH₃ gas concentration for the first time,which is one of the main air pollutants.In this paper,the development of cavity enhanced absorption spectroscopy is briefly introduced,and several absorption spectroscopy techniques are analyzed and compared.The theory of spectral quantitative analysis and various spectral linewidth broadening mechanisms are discussed.The mode theory of the resonant cavity and its resonant conditions and mode matching are discussed in depth.The application of HITRAN database in spectral simulation is briefly introduced.The absorption spectral line of NH₃ gas.In order to detect the concentration of NH₃ gas,the cavity-enhanced absorption spectroscopy system using the method of scanning the cavity length has been build up.In the system,a tunable DFB diode laser is used as the light source,and an optical cavity,which is consisted of two mirrors with high reflectivity?reflectivity is about 99.9% and radius of curvature r is about 1 m?,is used as the absorption cavity.The absorption spectroscopy of ammonia gas centered at 1.5 ?m can be obtained by using cavity length scanning method.And the linear correlation between the different gas line width and gas pressure was obtained by changing the concentration of NH₃ gas.Finally,the absorption spectrum under the minimum pressure is evaluated by Gauss fitting,and the residual noise is analyzed statistically.The minimum detection sensitivity of 3.3×10-8 cm^-1 is obtained.The experimental results show that the high detection precision can be obtained by using the cavity enhanced absorption spectroscopy with high detection sensitivity to detect the NH₃ gas concentration.In addition,cavity enhanced absorption spectroscopy technology,which is one of the main used gas detection methods,will have a huge space for development and broad market prospects because of its performance has an absolute advantage in all aspects of equipment,operation,stability,as one of the most important methods in the field of atmospheric environmental monitoring and detection.