The Study Of Long Path And Sensitive Methane And Aerosol Sensor

With the development of industrial techniques and proceeding of society,the atmosphere environment pollution becomes a prominent society problem which influences the living level of human being.The optical sensor on the basis of the laser spectrum can be effectively for the monitoring the atmosphere due to its characteristic of real time,high sensitivity and so on,some of them can be utilized in some field which require low sensitivity,point monitoring and single gas detection.But for the pollution trace gas in air,the characteristics become shortcomings.For the aerosol remote sensing,the wavelength of laser system has hazard to eyes of human being.For the problems mentioned above,the wavelength modulation technology,frequency comb technology and aerosol remote sensing technology in combination with long gas cell or the open-path scheme are adopted for all the problems.In the dissertation,the long gas cell is designed.We do the research on the point high sensitive sensor in near infrared(NIR)and mid infrared(MIR)by long gas cell.And monitoring methane over 3km is firstly realized by wavelength modulation spectroscopy,which can monitor gas in area district.For the multi-species gas detection,the frequency comb technology combined with long gas cell is used for the point sensor and open-path experiment.For the eye-safe laser wavelength,1.57?m aerosol laser remote sensing system is developed.The techniques developed are not only useful for the environment monitoring,but also for the medical field such as monitoring trace gas in human breath(Acetone).The related research is carried out.The main work in this dissertation are as follows:1.Introduce the basic theory of the absorption spectroscopy of molecules in IR.This chapter firstly presents important parameters of absorption lines,line shape functions,analyze the influence of temperature and pressure on the absorption line and line functions.Then,the principle of gas measurement by wavelength modulation spectroscopy,cavity ringdown spectroscopy and frequency comb spectroscopy are given.At last,it is concluded for the general scheme,laser source and detectors.2.Research on the high sensitive methane sensor in NIR and related work.Design and implement the long optical gas cell.The method of swept frequency optical interferometry is proposed for the length of the cell with high accuracy.Design and realize the digital-phase demodulated software.The high sensitive sensor in NIR is designed by the software in combination with the long gas cell,3.Research on sensor of the acetone and methane in MIR by interband cascade laser and frequency comb.Analyze the characteristic parameters of the interband cascade laser and the parameters of acetone spectrum.The high sensitive acetone sensor is designed by wavelength modulation and spectroscopy.The high sensitive methane sensor is also designed and implemented by the wavelength modulation spectroscopy and MIR long gas cell with length of 580 meters.Introduce the frequency comb spectroscopy technology,derive the principle of dual comb spectroscopy,design the methane and acetone sensor by frequency comb spectroscopy4.Research on the 1.57 ?m aerosol Lidar system,the open path systems by wavelength modulation spectroscopy and frequency comb.The lidar system is implemented by self-built laser source and the single photon counting detector.Realize the four channels digital lock in demodulation software,carry out the open path measurement system for measuring methane over 3km by wavelength modulation spectroscopy.The open path system by frequency comb is also built in our lab with length 39.6 meters,which can detect the methane and water simultaneously.The results are analyzed and compared under different experimental conditions.The innovations are summarized as follows:1.The long optical gas cell based on confocal principle with length 290 meters is firstly designed and realized.The proposed method of optical frequency sweeping can be effectively to improve the accuracy of length up to 20 times compared with absorption spectroscopy method2.The movable and high sensitive sensor in NIR is firstly designed and implemented,including the design of demodulation software,the built of the optical platform and performance experiment of sensor.The detect sensitivity can achieve 1.2 ppb.3.Design and implement the laser temperature controlling system on the basis of pulse width modulation and adaptive algorithm.The laser temperature can be effectively and quickly stabilized to 25 degree with resolution of 0.2 degree.The implemented algorithm has been utilized in the products of the company.4.The acetone sensor is firstly realized by the interband cascade laser and wavelength modulation spectroscopy with sensitivity 0.12 ppm.Another high sensitive methane sensor is also realized by the same technology and long gas cell with length of 580 meters.5.The acetone and methane sensor is firstly realized by the dual comb spectroscopy with detect ion sensitivity with sensitivity of 2 ppm and 60 ppb,respectively.6.The 1.57 ?m micro-pulse aerosol lidar system is firstly implemented by the self-built eye-safe solid laser on the basis of optical parameters oscillation and InGaAs APD single photon detector.7.It is first time to apply the wavelength modulation spectroscopy to open-path remote sensing of methane over 3 km with sensitivity of 10 ppb8.The open-path methane sensor is realized by MIR frequency comb.The errors are analyzed and compared under different conditions.