【作者】 贺元兴；

【导师】 姜文汉； 李新阳；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2012， 博士

【摘要】 在目前各种高功率激光装置的设计和研制过程中，除了需要解决提高激光输出功率（或能量）及改善光束质量的技术方案外，如何合理评价和可靠测量光束质量的问题关系到激光系统整体性能的评估结果，国内外学者均对该问题的研究十分重视。本论文紧密围绕激光光束质量这一核心要素，通过理论分析、数值仿真和实验验证相结合的方法，主要开展了如何客观评判现有各种激光系统的光束质量优劣、基于CCD所测得的远场光斑计算光束质量时如何来评估其计算误差以及从测量的角度如何提高激光远场和光束质量的测量精度三方面研究工作。论文首先以三种常见类型的激光束，即非稳腔产生的环形激光束、稳定腔产生的高斯光束以及多路高斯光束的相干合成光束作为研究和讨论的对象，针对能量型应用场合，分析了现有各种评价指标的优缺点和适用性，并对评价指标定义中理想参考光束和规范量的选取进行了分析计算。结果表明，激光束的亮度或靶目标上焦斑能量（功率）密度是较好的评价参数，该参数不仅与激光系统的应用目的关系密切，而且也适合于不同激光系统间性能优劣的横向比较，作为应用，进一步分析了单路激光发射口径、激光波长、中心遮拦比、发射窗口形状，及多路激光合成光束路数、填充因子、发射窗口截断等固有因素对激光系统性能的影响。将残留相位结构函数方法引入到计算部分相位补偿光束通过大气湍流的传播问题中，提出了一种新的计算部分相位补偿高斯光束和圆环形光束的远场光强分布的方法，并考察了前若干低阶泽尼克像差校正对接收面光斑质量的改善效果，并与国外文献的方法得到的相应计算曲线进行对比，二者吻合的很好，与国外文献的方法相比，新方法避免了计算十分复杂的数值积分，极大的减少了计算复杂度。此外，通过数值仿真方法研究了使高斯光束远场性能指标取得最大值时发射窗口最优截断系数的选取问题，给出了高斯光束发射窗口最优截断系数与湍流强度之间的拟合公式，该拟合公式在相当大的湍流像差范围内与实际真实情况吻合的较好，拟合相对误差小于7%。在光束质量测量误差分析方面，针对远场光斑为高斯型分布情况，同时考虑环境背景光噪声、CCD背景暗电平、CCD读出噪声、探测信号的光子起伏噪声以及CCD离散像素的采样误差的影响，从理论上推导出在采取不同的计算阈值时，峰值斯特列尔比、环围能量斯特列尔比以及光束质量β因子的误差公式，并通过数值仿真方法对所推导的误差公式进行了验证，仿真结果与理论计算结果吻合。研究结果表明，计算阈值对测量结果的影响很大，合理的阈值将使得光束质量评价参数的测量和计算误差较小，当阈值取为CCD背景电平均值加一倍噪声起伏是较好的一种阈值取法。提出了一种基于衍射光栅分光原理的二维成像器件光电响应特性的标定新方法，给出标定方法的理论依据、标定步骤，该方法是对双缝标定方法的扩展，有效解决了弱光不能标定的不足，并且通过有效的数据融合方法实现了不同组测量数据的融合、提高了标定采样点数。作为应用，利用该标定方法对某特性未知的红外CCD相机光电响应特性进行了实验标定，给出了实验标定结果。为分析CCD光电非线性响应对光束质量参数测量结果的影响，通过建立激光远场光强及描述CCD光电响应非线性特征的理论模型对其进行了深入分析。结果表明，CCD死区的存在使得远场光斑幅度较小的空间分布特征丢失，非线性饱和效应会造成远场光斑幅度较大的中心主核形态被压缩，二者对光束质量参数测量精度的影响不容忽视，为了减小它们的影响，对CCD光电响应特性的事先标定并做事后数据的修正以及采用焦斑重构方法以拓展CCD测量动态范围这两种方案是十分有效的手段。在如何提高激光远场和光束质量的测量精度方面，论文首先对目前各种拓展CCD相机动态测量范围方法的优缺点和适用性进行分析，在此基础上结合实验室的实际情况，选择衍射光栅作为分光元件，给出了一种基于衍射光栅的远场焦斑重构和测量的方法，对方法的基本原理、适用性进行了深入分析。为了验证该方法在拓展CCD测量动态范围，探测激光远场高频旁瓣能量分布信息方面的有效性，分别采用数值仿真和试验两种方法对方法的有效性进行验证，在此基础上进一步提出基于正交光楔的激光远场焦斑重构和测量的新方法，设计并搭建了实验方案和平台，对该远场测量新方法进行了实验验证。通过对远场PIB曲线、光束质量β因子等参数的分析对比，仿真和实验结果均表明论文所提远场测量新方法在拓展CCD动态范围方面是可行的。更多还原

【Abstract】 In the process of designing and manufacturing high power laser system, besidesinvestigating the technical scheme to increase the laser’s output power and improve itsbeam quality, it is enormously important for the estimation of overall performance oflaser system to evaluate reasonably and measure reliably, thus, people pay more andmore attention to the issues on laser beam quality. This paper places the beam quality ascore issue and is devoted to study three kinds of researches, i.e., the evaluation ofperformance of different laser system, error analysis of calculating laser beam qualitybased on far-field spot measured with CCD sensor, and enhancement of dynamic rangeof CCD sensor to improve the measurement precision of far-field spot and beam quality,in which the methods of academic analysis, numerical simulation and experimentalverification are used.First, according to application purposes concerning focusability of laser energy,three kinds of lasers, i.e., the annular lasers generated from unstable resonators,Gaussian lasers generated from stable resonators and combined lasers of severalGaussian lasers are taken as analyzing objects, the advantages and drawbacks of beamquality parameters available are discussed, and some key issues on definition of beamquality are calculated and analyzed. The results show that, the parameter of laserbrightness or laser energy density on the target is a very important standard forevaluating the performances of laser systems, which is suitable for measuringperformance of the same system, as well as different systems objectively. Furthermore,the laser energy density is used to investigate the influence of inherent factors, such aslaser wavelength, size of emission window, central obscuration ratio, shape of emissionwindow for single laser beam, and the number of sub-beam, duty ratio, truncation ratiofor coherently combined laser beam, on the far-field focusablity of different lasersystems.Residual phase structure function method is used, and a new method of calculatingthe modulation transfer function and far-field irradiance profile of a truncated Gaussianlaser and annular plane laser through atmospheric turbulence is proposed, the effects ofseveral lower-order aberration modes corrections on the spot quality in the receivedplane are investigated, the results derived in this paper agree well with the results ofcorrection reference, moreover, the complexity of this new method used here is superiorto the method used by correlation reference. Besides, the optimal truncation of theemission window to maximize the system performance is investigated by numericalsimulation, and the relationships between the coefficient of the optimal emissionwindow truncation and the turbulence strength are presented, which agree well with thereal situation over a considerable turbulence regime and the accuracy is better than7%. In the aspect of error analysis of measuring laser beam quality, taking the far-fieldGaussian spot as an example, the calculation error formulas of peak Strehl ratio,encircled energy Strehl ratio and beam quality factor β are derived in the present ofvarious error sources, such as background photon noise, CCD pixel’s non-idealsampling, CCD dark voltage, read-out noise of CCD, signal photon noise andmeasurement window size. The calculation errors of laser beam quality changing withvarious error sources are presented in theory and the corresponding numericallysimulated results are given. Theoretical and simulated results show that when thecalculation threshold is the sum of average value of the error sources and mean-squarevalue of the fluctuation in error sources, the lowest calculating error of laser beamquality could be achieved.A new method of calibrating2-D imaging device based on1-D linear diffractiongrating is proposed, and the theoretical foundation and calibration step are givenaccordingly. On the one hand, this new calibration method is extension of double-slitmethod and has higher light available ratio, on the other hand, the syncretization ofmultiple sets of measurement data expands the calibrating range of CCD camera andincreases the sampling data. As an application example, a series of1-D lineardiffraction gratings are designed and an infrared CCD camera with an unknowncharacter is calibrated.The far-field propagation model of annular plane beam through Kolmogorovatmospheric turbulence is presented and the nonlinear response characterization, such asso called dead zone and nonlinear saturation effect of CCD sensor are considered aswell, the influences of CCD’s nonlinear response characterization on the measurementresults of laser beam quality are investigated. The results show that, CCD’s dead zonecauses compression of center core of far-field spot and nonlinear saturation effectcauses loss of far-field intensity information with minor amplitude, and in order toreduce their influence, it is neecessary to calibrate the response characterization of CCDbeforehand and expand CCD’s measurement dynamic range.In the aspect of how to improve the measurement precision of far-field spot and itsbeam quality, firstly, the drawbacks and applicability of different method for expandingdynamic range of CCD sensor are analyzed, then, according to the far-field focal opticalsystem available in the laboratory, we choose diffraction grating as light splitting deviceand give a new method for measurement of far-field focal spot. Theoretical analysis,numerical simulation and experiment method are used to verify the validity of this newmethod. Furthermore, a new method for focal spot reconstruction and far-field focalmeasurement based on the orthogonal wedges is proposed, the beam quality factor aretaken as a useful evaluating measure, the theoretical model of intensity profiles of thedefocus spot is built and the laboratory scheme accordingly is implemented, theexperiment results show that the method given here is practicable.更多还原