Test Method And Exprimental Study For 2μm Coherent Doppler Wind Lidar System

2μm Coherent doppler wind lidar system is recognized as one of the most important means of the global atmosphere wind field measurement, due to its good time and spatial resolution, high measurement precision. Now, wind lidar have been applied in the field of aircraft safety warning and numerical weather prediction. This article mainly aims at the assembly and adjustment of Cassegrain telescope and the problem of free space 2μm laser and single-mode optical fiber coupling and 2μm laser divergence angle of core optical system in 2μm coherent wind lidar system. Then a set of test methods and verify the reliability of the method by experiments is proposed, which lay a solid foundation for the follow-up system assembly and field test. The main content of the dissertation includes:(1) Summarize Cassegrain telescope's structure and parameters, and theoretically introduce the primary differ and avefront aberration of the optical system. The article presents the assembly and adjustment of optical antenna by using ZYGO interferometer test method, and uses artificial-method to measure parameters of avefront aberration. Then the testing results of ZYGO interferometer and the theoretical design parameters are compared. The result of PV value is 0.101λ(2050nm) by computer calculation and 0.113λ(2050nm) by artificial-method to measure parameters, and inferior to the design requirementsλ/15.(2) Brifely introduces the method of testing the laser and put forward beam quality evaluation parameters. And then measure 2μm laser Gaussian beam waist and the divergence angle. Then we study the gaussian beam focus and alignment problems, and the coupling efficiency of gaussian beam to single-mode optical fibre . In addition, introduce off-axis aspherical collimator by Throlabs processing, and discusses matching problem between the laser divergence angle and coupling numerical aperture. Then we calculate the coupling efficiency for different numerical aperture and divergence Angle. Lastly, 2μm gaussian beam coupling experiment obtains the actual results of the coupling efficiency.(3) Using the existing 2um laser,Φ150mm Cassegrain telescope, Thorlabs'off-axis aspherical collimator and other devices, we constructed preliminarily coherent doppler wind lidar field experiment system and detected echo signal of the fixed objective to verify the feasibility of the method.