Study On Trace Gases Detection Based On Long Optical Path And Near Infrared Photoacoustic Spectroscopy

With the rapidly development of science and technology in recent years,there is a growing demand for highly sensitive gas detection systems in many fields,such as energy exploitation,electricity,atmospheric environmental monitoring,industrial emissions and medical treatment.Photoacoustic spectroscopy is a gas detection technology with high sensitivity,good stability,fast response and wide detection range.In this paper,the photoacoustic spectroscopy technique combining long optical path structure with resonant photoacoustic cell was studied and a good detection ability was realized.Based on the theory of photoacoustic spectroscopy technology,this paper analyses photoacoustic signal generation process in resonant photoacoustic cell and studies the influence of various factors on photoacoustic cell characteristics,the first-order longitudinal resonant photoacoustic cell was designed and the resonant photoacoustic system was built.In order to improve the detection ability,two growth optical path schemes were proposed,one is the double path structure based on conical mirror and the other is the long path structure based on the Herriott reflecting cell technology,and a set of Herriott reflecting mirrors were designed.In addition,the upper computer software was designed on Labview,and the functions of signal acquisition,data processing and data display are realized.Taking ammonia as the research object,the cross-effect of interfering gas on ammonia was analyzed by HITRAN database,and ammonia absorption spectrum line was determined at1531.6nm.The key parameters of the photoacoustic cell and the optimal tuning parameters of the light source are studied experimentally.A better operating parameters were determined.On the platform of the experiment,the response characteristics of the double path photoacoustic system and the long path photoacoustic system were studied by the ammonia concentration gradient measurement experiment.Among them,The double path photoacoustic system minimum detection limit was 457ppbv and normalized equivalent noise absorption coefficient was 1.68×10^-10W·cm^-1·Hz^-1/21/2 when the optimal average time was 436s.The long path photoacoustic system minimum detection limit was 269ppbv and the normalized equivalent noise absorption coefficient was9.87×10^-11W·cm^-1·Hz^-1/2when the optimal average time was 100s.The long optical path photoacoustic system has better rapidity,detection ability and reliability.A high sensitivity photoacoustic spectroscopy system is implemented in this paper.