Study On The Fiber Quartz Enhanced Photoacoustic Spectroscopy

In recent years,with the rapid development of industrialization,human activities have an increasing impact the atmosphere.Therefore,it is necessary to detect the ambience trace gas.Along with the advancement of laser device and laser spectroscopy,the researches of laser spectrum techniques for trace gas detection have become a new study field.Among these techniques,Quartz Enhanced Photoacoustic Spectroscopy(QEPAS),an advanced laser spectrum technique,has many merits,which has become the main trend in this field.In the conventional system of QEPAS,laser transmits usually via a pair of lenses which are used for collimating and focusing.However,the lens system always has an unstable structure and a large scale which make it not suitable for some gas detections,especially in some extremely conditions,like narrow space and adverse circumstances.Based on this situation,fiber has been utilized in the QEPAS system instead of lens group in this study.And some practical characteristics of fiber QEPAS system have been investigated.In this paper,the basic theory of QEPAS is introduced in the first place.The photoacoustic spectroscopy(PAS)and its traditional system have been analyzed;meanwhile,the QEPAS was presented.And the typical structure attached with the implementation process was described in detail.The quartz turning fork(QTF)which is the key component of QEPAS was introduced.Due to the special feature of quartz crystal,this paper gave a brief introduction to the basic characteristics of QTF and its electrical behavior in the circuit system.Then,the laser wavelength modulation technique in QEPAS was theoretically calculated.Based on the fundamental of gas infrared absorption,the QEPAS 2f signal as a function of laser modulation depth was established via a series of formula derivation.In addition,the optical field of the cross section in the fiber was simulated using the finite element software COMSOL Multiphysics.The results showed that there was a optimal modulation depth in QEPAS system,and smaller diameter of fiber had stronger evanescent waves.At last,the experiments of QEPAS based on fiber spatial optical path were performed.We firstly posed a new broach where a fiber beam splitter was employed to conducted multi-point detection and demonstrated the potential of spatially resolved measurements.In addition,the fiber evanescent waves of QEPAS experiments were developed.Based on fiber evanescent wave technique,we firstly carried out a novel method for multi-point detection and spatially resolved measurements.And the results of experiments illustrated that there were two effective schemes in QEPAS system with trace gas detection.The works of this study enriched the fiber-QEPAS technique in gas detection research fields.