基于自适应光学的激光束整形系统研究

发布时间：2018-12-29 10:30

【摘要】：由于自身良好的特性,激光自发明以来就得到广泛的应用。但是随着科学技术的发展,高斯光束已不能满足实际应用中对光束形态与能量分布的要求。激光束整形技术应运而生。利用该技术对高斯光束进行整形,以获取满足应用要求的激光束。在众多激光束整形技术中,基于自适应光学的激光束整形技术最具潜力和发展前景。它通过控制变形镜面形调制入射光场复振幅分布,以实现光束整形,因而具有控制灵活、适应性好、面形多样化、光能传输效率高、损伤阈值高等特点。但是,现有研究缺乏激光束整形系统的系统分析以及变形镜参数对系统性能影响的研究。为了充分了解并发挥基于自适应光学的激光束整形系统的性能,本文对其进行了一系列深入详细的分析研究。第一,为了对激光束整形系统性能进行量化分析,本文建立了基于近场调制位相与远场整形光强的系统性能评价指标体系,包括近场调制位相的PV与RMS值,远场整形光强的相关系数与光强偏离残差平方和均值。第二,近场调制位相是激光束整形系统研究的重要对象。由于方形或圆形均匀目标光强自身的数学特性,近场调制位相近似解可通过积分渐近近似方法获取。为了解决积分渐近近似法的局限性,本文提出一种基于泽尼克模式的随机并行梯度下降算法以获取近场调制位相。第三,目标光强形态大小是激光束整形系统的一个重要参数,不仅对近场调制位相分布有着直接影响,也会影响远场整形光强。本文利用拉格朗日乘数法等数学方法,分析目标光强形态大小对近场调制位相及远场整形光强的影响。第四,光瞳截断作用直接影响入射光场及近场调制位相分布,并间接影响远场光强整形性能。在研究光瞳截断作用对远场光强整形性能影响规律的基础上,本文建立远场光强整形性能评价指标关于光瞳半径及目标光强形态大小参数的数学模型。根据数学模型,本文提出一种最优光瞳半径的选取方法。第五,变形镜是基于自适应光学的激光束整形系统的核心位相调制元件。变形镜面形由驱动器影响函数及控制电压决定。本文研究了变形镜影响函数数学模型中的参数:驱动器间距、交连值及高斯指数,对激光束整形系统性能的影响。其中的变化规律,为变形镜参数选择提供依据。第六,激光束整形系统研究目标是获取与目标光强尽可能相似的远场整形光强。变形镜拟合近场调制位相常用方法是最小二乘法,可以获取最小拟合误差。本文分析了最小拟合误差与最优远场整形性能的关系,发现最小拟合误差并不对应最优远场整形性能。在此基础上,本文提出了一种基于最小二乘法的随机并行梯度下降优化算法,并利用该方法进行近场调制位相拟合,激光束整形系统性能有明显提升。第七,本文研究近场调制位相分布特性,并据此选择变形镜,搭建基于Bimorph的无波前探测激光束整形系统,利用随机并行梯度下降控制算法完成方形均匀目标光强整形实验。第八,为弥补单变形镜激光束整形系统的不足,本文利用Bimorph变形镜、3mm极间距PZT变形镜以及夏克-哈特曼波前探测器,搭建基于双变形镜的激光束整形系统。利用直接斜率法闭环实现远场方形与圆形均匀目标光强整形实验。为了验证变形镜拟合方法对远场整形性能影响,利用直接斜率法获取的控制电压为初始值,通过双扰动随机并行梯度下降算法继续优化电压。对比发现,随机并行梯度下降算法优化电压有利于远场光强整形性能提升。
[Abstract]:Due to its good characteristics, the laser has been widely used since the invention. However, with the development of science and technology, the Gaussian beam has not been able to meet the requirement of the beam form and energy distribution in the practical application. Laser beam shaping technology has come into being. The Gaussian beam is shaped by the technique to obtain a laser beam that meets the application requirements. In many laser beam shaping techniques, the laser beam shaping technology based on the adaptive optics is the most promising and promising. The invention has the characteristics of flexible control, good adaptability, diversified surface shape, high light energy transmission efficiency, high damage threshold and the like by controlling the complex amplitude distribution of the incident light field by controlling the deformation mirror-shaped modulation. However, the present study lacks the systematic analysis of the laser beam shaping system and the study of the effect of the deformation mirror parameters on the performance of the system. In order to fully understand and give full play to the performance of the laser beam shaping system based on adaptive optics, a series of in-depth and detailed analysis of the laser beam shaping system is carried out. First, in order to carry out the quantitative analysis of the laser beam shaping system performance, the system performance evaluation index system based on the near field modulation bit phase and the far field shaping light intensity is established, including the PV and RMS values of the near field modulation bit phase, The correlation coefficient of the far field shaping light intensity and the light intensity deviate from the mean square of the residual sum of the residual. Second, the near field modulated phase is an important object of the laser beam shaping system. The approximate solution of the near field modulation bit can be obtained by the integral asymptotic approximation method due to the mathematical characteristics of the square or circular uniform target light intensity. In order to solve the limitation of the integral asymptotic approximation method, a random parallel gradient descent algorithm based on Zernike mode is proposed to obtain the near field modulation bit phase. Thirdly, the size of the target light intensity is an important parameter of the laser beam shaping system, which not only has a direct influence on the distribution of the near field modulation bit, but also affects the light intensity of the far field. In this paper, by using the Lagrange multiplier method and other mathematical methods, the influence of the size of the target light intensity on the light intensity of the near field modulated phase and the far field is analyzed. Fourth, the optical pupil truncation effect directly affects the distribution of the incident light field and the near field modulation bit, and indirectly influences the light intensity shaping performance of the far field. On the basis of the study of the influence of the optical pupil truncation on the light intensity shaping performance of the far field, this paper sets up a mathematical model of the optical pupil radius and the parameter of the shape and size of the target light intensity. According to the mathematical model, this paper presents a method for selecting the optimal pupil radius. Fifth, the deformable mirror is a core bit phase modulation element based on the adaptive optics laser beam shaping system. The deformation mirror shape is determined by the driver influence function and the control voltage. In this paper, the parameters in the mathematical model of the influence function of the deformable mirror are studied: the driver spacing, the intersection value and the Gaussian index, and the effect on the performance of the laser beam shaping system. The rule of variation is to provide the basis for selecting the parameter of the deformable mirror. Sixth, the aim of the laser beam shaping system is to obtain a far field shaping light intensity that is as close as possible to the target light intensity. The common method of fitting the near field modulation bit by the deformable mirror is the least square method, and the minimum fitting error can be obtained. In this paper, the relation between the minimum fitting error and the optimal far field shaping performance is analyzed, and it is found that the minimum fitting error does not correspond to the optimal far field shaping performance. On this basis, a random parallel gradient descent optimization algorithm based on the least square method is proposed, and the near field modulation bit is fitted by the method, and the performance of the laser beam shaping system is obviously improved. Seventh, this paper studies the distribution characteristics of the near-field modulation bit, and then selects the deformable mirror, sets up a non-wave front-probe laser beam shaping system based on the Bimorph, and uses the random parallel gradient descent control algorithm to complete the square uniform target light intensity shaping experiment. In order to make up for the defects of the laser beam shaping system of the single-deformable mirror, the laser beam shaping system based on the double-deformable mirror is set up by using the Bimorph deformable mirror, the 3mm-pole pitch PZT deformable mirror and the summer-Hartmann wave front detector. The direct slope method is used to realize the light intensity shaping experiment of the far field square and the circular uniform target. In order to verify the influence of the fitting method of the deformation mirror on the shaping performance of the far field, the control voltage obtained by the direct slope method is the initial value, and the voltage is continuously optimized by the double-disturbance random parallel gradient descent algorithm. It is found that the optimized voltage of the random parallel gradient descent algorithm is favorable for the improvement of the light intensity shaping performance of the far field.
【学位授予单位】：中国科学院研究生院(光电技术研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN249

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