大功率空间椭圆光束整形和传输研究

发布时间：2018-07-18 15:29

【摘要】：空间激光通信对通信质量与通信稳定性有很高的要求。在信号发射源的选择上,半导体泵浦的固体激光器具有构造简洁、使用寿命长、高效稳定的优势,出射的激光光束具有输出功率高、光束质量高、稳定性高的特点。在固体激光器的选择中,板条型激光器由于具有良好的导热性能而成为首选。本论文针对板条型固体激光器出射的在大气中传输的椭圆激光光束的光束发散角、束腰半径以及整形后光束所受大气散射引发的成像光斑作出以下几方面的研究：(1)对板条激光器与空间激光光束整形传输的概况简要介绍,重点综述板条型激光器的优势与近年的发展状况、光束整形的分类与近年发展状况以及空间激光传输研究的发展状况。(2)介绍了以光学变换矩阵为主的光束传输特性研究方法、基模高斯光束的描述与质量评价方法以及高斯光束的ABCD定律应用。(3)分析了大气中粒子引起的Mie散射的理论基础以及粒子的形状、尺度参数、粒子的折射率对散射的影响,阐述了Mie散射的强度分布函数、体角散射函数的计算方法。(4)针对板条激光器输出光束光斑呈椭圆形的问题,采用几何方法设计整形系统,运用ABCD定律,选用五组不同焦距的柱面凹凸透镜组合,模拟了运用柱面望远镜系统对椭圆光束横轴方向进行扩束、并用单波长扩束装置压缩激光横轴与纵轴方向远场发散角的方法。仿真结果为：选取特定组合焦距的柱面凹透镜与柱面凸透镜,可将激光光束横轴方向的较大的初始发散角由600 μrad减小到230 μrad,同时使两轴的束腰位置保持相同。通过普通扩束镜对光束进行横轴、纵轴两方向的同时扩束,扩束后横轴、纵轴两方向远场发散角的比值接近于1。在实验中最终也得到了整形后横轴发散角为92.8 μrad、纵轴发散角为107 μrad的圆形高斯光束,与仿真结果相符合。(5)整形后激光光束在大气中传输时会受到后向散射,针对后向散射在CCD接收屏上的光斑形状问题,分别通过理论与实验进行研究。理论上,首先分析大气激光传输的比尔定律和后向Mie散射的散射光强度函数；其次推导出成像光斑圆心位置及半径计算公式,构建大气分层模型,激光光束被分割为若干层分别在接收屏上成像,通过对成像光斑进行叠加从而得到后向散射总光强,得出成像光斑后向散射总光强与大气颗粒物浓度成正比的结论。实验上,通过控制出射光束的基本参量保持不变,获取大气颗粒物浓度不同情况下的Mie后向散射CCD成像图。实验结果与仿真结果相符,对不同大气颗粒物浓度下的实验结果进行对比分析,为研究大气中其他光束的后向散射成像打下基础。
[Abstract]:Space laser communication has high requirements for communication quality and communication stability. The semiconductor pumped solid-state laser has the advantages of simple structure, long service life, high efficiency and stability. The output laser beam has the characteristics of high output power, high beam quality and high stability. In the selection of solid-state lasers, lath lasers are preferred because of their good thermal conductivity. In this paper, the beam divergence angle of elliptical laser beam propagating in the atmosphere is studied. The beam waist radius and the imaging spot caused by atmospheric scattering after beam shaping are studied in the following aspects: (1) the general situation of beam shaping and propagation of slab laser and space laser beam is introduced briefly. The advantages and development of slab lasers in recent years, the classification and development of beam shaping in recent years and the development of space laser propagation are reviewed. (2) the research methods of beam propagation characteristics based on optical transformation matrix are introduced. The description and quality evaluation of the fundamental mode Gao Si beam and the application of the ABCD law of the Gao Si beam. (3) the theoretical basis of the Mie scattering caused by the particle in the atmosphere and the influence of the particle shape, scale parameters and the refractive index of the particle on the scattering are analyzed. The intensity distribution function of Mie scattering and the calculation method of volume angle scattering function are described. (4) aiming at the problem that the beam spot of slab laser output beam is elliptical, the shaping system is designed by geometric method, and the ABCD law is used. Five groups of cylindrical concave and convex lenses with different focal lengths are selected to simulate the method of beam expansion in the transverse direction of elliptical beam using cylindrical telescope system and the method of compression of far field divergence angle of laser transverse axis and longitudinal axis with a single wavelength beam expander. The simulation results are as follows: when the cylindrical concave lens and the cylindrical convex lens are selected, the larger initial divergence angle of the laser beam in the transverse axis direction can be reduced from 600 渭 rad to 230 渭 rad, and the waist position of the two axes can be maintained at the same time. The ratio of far field divergence angle between the two directions after beam expansion is close to 1. The beam is expanded at the same time in both directions of the longitudinal axis and the transverse axis of the beam through the common beam expander mirror, and the ratio of the far field divergence angle in the two directions after the beam expansion is close to 1. In the experiment, a circular Gao Si beam with a transverse divergence angle of 92.8 渭 radand a longitudinal axis divergence angle of 107 渭 rad is obtained, which agrees with the simulation results. (5) the laser beam after shaping will be backscattered when it propagates in the atmosphere. Aiming at the problem of the spot shape of backscattering on CCD receiving screen, the theoretical and experimental studies are carried out. In theory, Beer's law of atmospheric laser propagation and scattering intensity function of backward Mie scattering are analyzed firstly, and then the calculating formulas of center position and radius of imaging spot are derived, and the atmospheric stratification model is constructed. The laser beam is divided into several layers to image on the receiving screen respectively. The total backscattering light intensity is obtained by superposing the imaging spot, and the conclusion that the total backscattering light intensity of the imaging spot is proportional to the concentration of atmospheric particulates is obtained. By controlling the basic parameters of the beam to remain unchanged, the Mie backscattering CCD imaging images with different concentrations of atmospheric particles are obtained experimentally. The experimental results are in good agreement with the simulation results. The experimental results under different concentrations of atmospheric particles are compared and analyzed, which provides a basis for the study of backscattering imaging of other light beams in the atmosphere.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN929.1;TN24

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