节点文献
可用于瞬态激光波前畸变实时检测技术的研究
【作者】 杨甬英；
【导师】 卓永模；
【作者基本信息】 浙江大学 ， 光学工程， 2002， 博士
【摘要】 激光核聚变研究是人类解决未来能源危机及改善严重环境污染的一项重大举措。该研究需要光机电等多学科的技术支持以保证高能激光束具有很好的光束空间特性。而激光系统波前畸变检测则是激光束空间参数诊断中的一个主要环节，本论文主要研究可用于瞬态(单幅干涉图)波前实时检测的径向剪切干涉体系、剪切波前的复原及重构技术、测量数据及图像处理技术。该研究对我国激光聚变系统的相关研究具有极为重要的意义。主要研究工作有： 论述了激光核聚变系统研究中波前畸变检测的重要意义。对国内外各种波前畸变的检测技术做了系统的分析，在此基础上提出利用线性载波可用于动、静态检测的空间位相调制的径向剪切干涉体系，并建立了初步的实验装置。 提出了激光波前近场、远场测量的光路布局及处理流程的系统框图。作了几部分的理论推导：以检测的相对灵敏度为依据、根据激光束的输入的光束口径、波前畸变大小，导出了与环型干涉系统的望远镜放大率有关的径向剪切放大倍数的确定；根据高能激光束超高斯型的特殊振幅轮廓有别于通常的平面波、球面波振幅的特点，以夫朗和费衍射理论为基础，导出了根据振幅轮廓的表征能量分散度特征的斯特列尔比；给出了激光束空间参数诊断的所有参量的诊断数学模型。 根据激光核聚变系统中光学系统具有圆瞳及矩形出瞳的特点。详细分析及推导了线性载波的空间位相调制的离散付氏变换的过程及产生混迭效应、频域泄漏效应的原因及影响，提出了分别适用于圆形及矩形出瞳的调制窗函数，尤其是用于矩形窗的金字塔窗函数。对解决激光聚变系统大量矩形出瞳的波前检测是很有利用价值的。并分析讨论了载波大小设定、滤波器的宽度、移频不移中等问题及相互之间的联系。上述模型流程的仿真计算达到了1／1000波长的计算精度。 研究了适用于圆形及矩形出瞳的径向剪切波前的重构理论及物理意义。利用迭代法以及解析法对剪切波前进行复原。尤其是解析法利用系数比较的Zernike正交多项式，可直接对径向剪切波前进行波前重构，并给出象差特征。对上述模型进行 浙江大学博士学位论文 了大量的仿真计算，可达到（2～3）／1000波长的均方根精度。 利用建立的实验装置，该系统对一象差透镜进行了从径向剪切干涉图——付 氏变换处理——剪切波前的系统比较的Zernike正交多项式拟合而得出重构波前 的整个流程及处理结果，得出了与实际一致的结果。并对整个处理过程进行了误差 分析，初步估算该测量方法可以达到门 ／10～1／20）X的均方根测量精度。 本论文研究的主要创新有：根据高能激光束超高斯型的特殊振幅轮廓，导出了 依据振幅轮廓的表征能量分散度特征的斯特列尔比及激光波前近场、远场空间特性 参量诊断流程的数学模型及物理意义；在详细分析了DPT频域泄漏效应原因的基础 上，首先提出了适用于矩形出瞳的金字塔形的滤波窗函数，其可有效地抑制频域泄 漏；全面、系统地推导了适用于圆形及矩形出瞳的径向剪切波前的重构理论、物理 意义和算法，利用迭代法以及解析法对剪切波前进行了波前重构及验证。
【Abstract】 The research of Inertial Confinement Fusion (ICF) technique is helpful to solve the problems of resource in future on earth and improve the pollution in the environment. The work based on the supporting many subjects such as optics, mechanics and electronics etc. It is a critical part to measure the wavefront distortion and divergence of pulse laser because the wavefront quality of the laser beam ultimately determines the focus ability of pulse wavefront. The thesis described some research work such as the system of a radial shearing interference being suited to measure static and dynamic wavefront, the reconstructed technique of the radial shearing wavefront and the processing technique of measuring data and the image. Main research work and new ideas as below:The importance of qualifying the wavefront distortion in ICF system is recounted. A number of sensing techniques of wacefront are analyzed and a radial shearing interference system with spatial linear carrier modulation suited to static and dynamic wavefront. A basic experiment device has been set up.In terms of the concept of relative sensitivity of measurement and the size of beam aperture of input system and the amount of the wavefront distortion, the radial shearing ratio relation with the magnification of a telescope is derived. A mathematic equation of Strehl ratio based on a amplitude model has been derived from the character of pulse laser and KirchhofFs diffraction theory.The most important error source in DFT method of the reconstructed wavefront is energy leakage effect. How to result in leakage and reduce the error are discussed in chapter 3 both modulation filters of Hamming and Pyramid windows are respectively applied to circular and rectangular pupils. Especially it is useful that Pyramid filterto rectangular elements in ICF can efficiently reduce the frequency leakage and obtain finer reconstructed wavefront. At the same time determining the amount of linear carrier f0, the width of filter of+1 order spectrum and slope at space domain result from the error of shifting +1 order to origin at frequency domain, which are analyzed in all details. Two methods that can carry out the reconstructed of radial shearing wavefront of iteration and analysis with Zernike orthogonal polynomial fitting are discussed. The mathematic models, physical explanations and data simulations of these algorithms are alldemonstrated in chapter 4. The accuracy of root-mean-square values of data simulations can be better than (2-3)71000 wavelength.To set up an experiment device of radial shearing interferometer with spatial linear carrier and carried out a series of data processing from DFT, IDFT, unwrapped, removed the slope to iteration or Zernike polynomial fitting. The results of wavefront measured are identical with practical conditions. The theoretical derivations and measurement results showed that the sensing system in thesis can attain a RMS accuracy of 1/10 ~ 1/20 wavelength.