Experimental Research On Raman Lidar For Water Vapor Measurements Based On Fiber F-P Filter

As an important atmospheric meteorological parameter,water vapor plays an important role in the study of weather changes,global hydrological cycle and atmospheric science.Raman scattering lidar has become one of the most effective methods for atmospheric water vapor measurements.At present,considering such deficiencies as non-compact structure,complexity of optical adjustment for the general spectroscopic Raman system,study on compact and reliable Raman spectroscopy technique has important scientific significance and research value for lidar application and the development of airborne or and space-based lidar technology.Aiming at some problems in the realization of all-fiber water vapor Raman spectroscopy system previously proposed,an optimized fiber Raman spectroscopic system based on fiber F-P filter is proposed and implemented in this thesis.Considering the coupling efficiency betweein different fiber-core fibers,an efficient optical coupling system using a self-focusing lens is firstly completed by Zemax simulation,and the maximum coupling efficiency up to 10%is achieved by experimental verification.Secondly,a set of dichroic mirror with long-wavelength pass filter is designed to ensure high inhibition rate to elastic scattering signals.On the basis of fiber F-P filters first developed in visible wavelength domain,the optimized fiber Raman spectroscopic system is built,and the optical properties of main fiber devices and the optical splitter system is tested.The experimental results showed that the spectroscopic system can successfully achieve fine extraction of Raman scattering signal of water vapor and nitrogen molecules,with central wavelength of 660 nm and 606.7 nm respectively,and achieve the efficient suppression of 107 to elastic scattering signal in the fiber channels,which validate that the optimized spectroscopic system satisfied the design requirements.Relying on the Lidar Atmospheric Remote Sensing Center in Xi'an University of Technology,the fiber spectroscopic Raman lidar system was built,and atmospheric water vapor measurements and related data retrieval were carried out.The preliminary results show that effectively detection range from the bottom to the several hundred meters can be obtained for water vapor measurement under the condition of laser energy of 200 mJ,telescope diameter of 600 mm,detection time of 15 minutes,and photon-counting mode.The continuous observation results also proved for the spatial-temporal variation of water vapor mixing ratio at night,which verified the detection performance of lidar system for water vapor measurements.