基于衍射传输的激光远距离聚焦特性分析及评价

发布时间：2018-05-21 00:34

  本文选题：衍射传输 + 光束质量　； 参考：《中国科学院研究生院(长春光学精密机械与物理研究所)》2016年博士论文

【摘要】：将高功率激光聚焦到远距离目标,获得高能量密度光斑分布,对国防、工业加工、制造领域有较大价值。从激光发射系统设计,到光场自由空间传输,再到激光聚焦光斑的反馈评价,涉及到大量建模、参数选取以及结构设计问题,通过仿真方法对系统进行合理设计与优化,能够节省大量成本与时间上的耗费。衍射光学是现代光学工程的基本方法之一,利用衍射传输能够满足激光远距离聚焦传输的仿真要求。本文在激光的衍射传输理论基础上,提出了适合激光聚焦仿真的改进算法,对仿真中激光的模式以及部分相干问题进行详细讨论,结合具体的聚焦系统设计,仿真分析了各种系统参数对远距离聚焦的影响并进行实验验证。另外提出了基于回波散斑的激光聚焦光斑反馈评价方法,能够对聚焦尺度进行高精度监视,使本文涵盖了激光发射、传输与反馈评价的仿真闭环,达到对系统工作性能的全面分析与评估。本文包含的主要工作如下:1.在标量衍射理论、激光光束传输基本理论以及现有的激光光束质量评价指标基础上,提出了对不同状态(初始光场分布、光束的相干性、传输环境等)的激光光束传输进行仿真的算法。首先,为了仿真光束经理想光学系统传输,在Collins衍射积分与线性调频Fourier变换(CFT)基础上,提出了宽窗口角谱算法(WWAS)。CFT的应用可以使输入输出空间域与空间频率域采样分离,在选取大计算窗口时不增加算法计算负担,解决了传统角谱法在仿真激光远距离传输时信噪比迅速下降的问题,而且输入与输出空间域的独立使得算法采样更加灵活。另外,基于信噪比分析方法对WWAS算法采样条件进行推导与验证。在自由空间传输条件下,对比了wwas算法与其它角谱法的传输效果,给出了该算法的优势。其次,为了仿真多模部分相干激光光束传输问题,提出了基于光强分布测量进行激光模式分解的线性方程组方法,利用该方法不但能够获得相干模式系数的能量分布,而且通过有限次纵向光强分布测量,得到不同模式之间的相关性差异。仿真中采用构造光束的方法对理论进行了验证。已知激光模式分布后,提出了一种部分相干激光的仿真方法,在兼顾了fft算法的高效性同时,保证了部分相干光束传输仿真的精度。2.在光束传输算法基础上,对激光远距离聚焦系统聚焦特性进行分析。首先利用zemax软件,设计了激光远距离聚焦系统,对系统的几何参数、激光参数、焦移量以及调焦曲线进行计算。利用光束传输算法分析了系统孔径截断带来的衍射损耗与聚焦光斑能量密度分布变化,与广义m2因子的评价方法进行对比分析,给出广义m2因子在受到孔径衍射聚焦系统中的评价作用。对于聚焦系统公差与调焦补偿误差,在像差衍射理论基础上,提出了zemax与matlab联合仿真的方法,zemax为光束传输算法提供出瞳像差,仿真计算得到聚焦光斑分布,可以分析公差分配是否合理,并给出合理的补偿方案。随后,采用实验方法对聚焦光斑能量分布、光斑形态进行测量,验证了仿真分析的正确性。另外,理论分析了大气湍流对激光光束传输的影响,并且对激光经大气扰动后m2因子的变化进行研究,给出了在无自适应系统时激光光束质量与大气扰动间存在的权衡关系。3.研究了基于目标回波散斑统计特性的激光聚焦光斑尺度监视与反馈技术。对于静态或缓慢运动目标,提出了两种散斑评价因子对激光聚焦光斑尺度进行评价:二值化散斑自相关评价因子(csam)由散斑的自相关函数计算得到,随光斑尺减小而增大;二值化散斑边缘积分(csei)评价因子对回波散斑的像进行二值化与边缘提取操作,csei因子随聚焦光斑尺度减小而减小;本文仿真分析了接收系统参数、目标粗糙程度、有限数据长度等因素对两种评价因子的精度影响,通过实验验证了理论分析结果,证明了两种评价因子对聚焦光斑的评估能力。对于快速运动目标,提出了利用双探测器信号相关进行光斑尺度评价的方案,通过matlab编程对该评价方案进行建模,证明了该方案的正确性,仿真分析了双探测器距离、数据长度等因素对探测精度影响,探讨了该方法对光斑尺度的探测极限及其可用性。
[Abstract]:It is of great value for the field of national defense, industrial processing and manufacturing to focus high power laser on long distance target and obtain high energy density light spot distribution. From the design of laser emission system to free space transmission of light field and feedback evaluation of laser focused spot, a large number of modeling, parameter selection and structural design are involved. The method of rational design and optimization of the system can save a lot of cost and time. Diffraction optics is one of the basic methods of modern optical engineering. The diffraction transmission can satisfy the simulation requirements of laser long distance focusing transmission. On the basis of the theory of laser diffraction transmission, this paper puts forward the modification of laser focusing simulation. In the algorithm, the mode of laser and the problem of partial coherence are discussed in detail. Combined with the specific design of the focusing system, the influence of various system parameters on the long distance focusing is analyzed and the experimental verification is carried out. In addition, a laser spotlight feedback evaluation method based on the echo speckle is proposed, which can improve the focus scale. Precision monitoring makes this article cover the simulation closed loop of laser emission, transmission and feedback evaluation to achieve a comprehensive analysis and evaluation of the performance of the system. The main work included in this paper are as follows: 1. on the basis of the scalar diffraction theory, the basic theory of laser beam transmission and the existing laser beam quality evaluation index, the different shapes are proposed. The simulation algorithm of laser beam transmission of state (initial field distribution, coherence of beam, transmission environment, etc.) is proposed. First, on the basis of Collins diffraction integral and linear frequency modulation Fourier transform (CFT), the application of wide window angle spectrum algorithm (WWAS).CFT can be used to make the input and output space domain. In separating the spatial frequency domain sampling, it does not increase the calculation burden of the algorithm when selecting the large computing window. It solves the problem of the rapid decline of the signal to noise ratio when the traditional angular spectrum method is used to simulate the long distance transmission of the laser. Moreover, the independence of the input and output space makes the algorithm sampling more flexible. Furthermore, the WWAS algorithm is sampled based on the signal to noise ratio analysis method. Under the condition of free space transmission, the transmission effect of wwas algorithm and other angular spectrum method is compared, and the advantages of the algorithm are given. Secondly, in order to simulate the transmission problem of multimode partially coherent laser beam, a linear equation group method based on the intensity distribution measurement for laser mode decomposition is proposed, and the method is used to use the method. Not only can the energy distribution of the coherent mode coefficient be obtained, but the correlation difference between different modes is obtained through the measurement of the finite longitudinal intensity distribution. The theory is verified by the method of constructing the beam in simulation. After the distribution of the laser mode, a simulation method of the partial coherent laser is proposed, and the FFT calculation is taken into account. The efficiency of the method also ensures the accuracy of the simulation of partially coherent beam transmission. Based on the beam transmission algorithm, the focusing characteristics of the laser long distance focusing system are analyzed. First, the laser distance focusing system is designed by using ZEMAX software, and the geometry parameters, laser parameters, focal shift and focus curve of the system are calculated. The beam propagation algorithm is used to analyze the variation of the diffraction loss and the distribution of the energy density of the focused spot caused by the aperture truncation of the system. The evaluation method of the generalized M2 factor is compared with the generalized M2 factor evaluation method, and the evaluation of the generalized factor in the aperture diffraction focusing system is given. On the basis of the theory, the method of joint simulation of ZEMAX and MATLAB is put forward. ZEMAX provides pupil aberration for the beam transmission algorithm. The distribution of focused spot is obtained by simulation calculation. It can analyze the rationality of tolerance distribution and give a reasonable compensation scheme. Then, the experimental method is used to measure the energy distribution of the focusing spot and the shape of the spot, and the imitation is verified. In addition, the effect of atmospheric turbulence on laser beam transmission is theoretically analyzed, and the change of M2 factor after the atmospheric disturbance is studied. The trade-off relationship between laser beam quality and atmospheric disturbance in the non adaptive system is given..3. studies the laser based on the statistical characteristics of the target echo speckle. Focused spot scale monitoring and feedback technology. For static or slow moving targets, two speckle evaluation factors are proposed to evaluate the laser focused spot scale. The two value Speckle Autocorrelation evaluation factor (CSAM) is calculated by the autocorrelation function of speckle, and increases with the decrease of the spot size; the two value speckle edge integration (csei) evaluation is the cause. The image of the echo speckle is two value and edge extraction, and the csei factor decreases with the reduction of the focus spot size. This paper simulates the influence of the parameters of the receiving system, the degree of target roughness and the length of the finite data on the accuracy of the two evaluation factors. The results of the theoretical analysis are verified by the experiment, and the two evaluation factors are proved. For the evaluation of the focus spot, a scheme to evaluate the spot scale using the correlation of dual detector signal is proposed for the fast moving target. The evaluation scheme is modeled by MATLAB programming, and the correctness of the scheme is proved. The influence of the distance of the dual detector and the length of the data on the detection accuracy is simulated and analyzed, and the results are discussed. Methods the detection limit and availability of spot scale are discussed.
【学位授予单位】：中国科学院研究生院(长春光学精密机械与物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN24
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本文编号：1916954