基于相干调制成像的高功率激光光束波前测量方法研究
文献类型：学位论文
| 作者 | 陶华 |
| 学位类别 | 博士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘诚 |
| 关键词 | 高功率激光 波前测量 相位恢复 相干调制成像 |
| 其他题名 | Research of Methods for Wave-front Measurement of High-power Laser Beam Based on Coherent Modulation Imaging |
| 中文摘要 | 用于惯性约束聚变(ICF)的高功率激光驱动器是一项规模庞大、精度要求极高的系统工程，其光路内采用了大量高精度和大尺寸的光学元件。在光学元件加工、安装和运行过程中，例如划痕、表面损伤、表面污染、灰尘颗粒等“缺陷”，安装方式的不当，重力作用下的表面变形，热积累效应等都会对光学性能产生不良的影响。光学元件导致的任何偏差最终会影响传输光束的波前质量。另外，激光光束从种子光源发出然后经过数百米的距离传输最终到达靶场系统，在这个过程中气流、温度等环境的变化也会对激光光束的质量造成影响。所有因素导致的光束质量下降使得照射到靶丸上的焦斑形态无法到达设计指标。在实际的高功率激光装置里面采取了多种技术手段对光束波前进行控制和纠正，但是只有准确地知道波前的形态、变化程度和位置等信息，才能采取有效的措施进行控制和改善光束质量，因此对于高功率激光光束的波前测量十分重要。 实际的高功率激光装置中采用的是脉冲激光，波前信息在相当短的时间内很难获取，并且由于装置内部空间非常有限，像干涉法这种传统的波前测量方法无法得到采用，因为干涉方法测量需要高度隔振的大型光学平台和规整的平行或者球面参考光，系统比较复杂，对工作环境要求高。目前高功率固体激光器输出光束的波前一般采用自适应光学系统中的哈特曼波前传感器进行测量，但是由于其微阵列透镜数量的限制，测量精度十分有限，并且难以测量大的相位梯度，无法满足高功率激光驱动器的波前测量要求。因此有必要研究高功率激光光束波前测量新方法。 相干调制成像(Coherent Modulation Imaging，简称CMI)是一种新兴出现的相干衍射成像(Coherent Diffractive Imaging)方法，是在PIE(Ptychography Iterative Engine)方法的基础上发展而来的。待测激光光束穿过一块具有已知相位结构分布的随机相位板，通过CCD相机记录其形成的衍射光斑。待测光束的波前分布可以利用CMI算法从所记录的衍射光斑强度快速地迭代重构出来。CMI方法结构上只包含一块随机相位板和一台CCD相机，十分简单、小巧；并且它还具有算法收敛速度快、对测量环境和CCD动态响应范围要求低、空间分辨率和测量精度高等诸多优点。本论文基于CMI方法，对高功率激光驱动器中波前测量方面遇到的问题展开研究，主要研究内容如下： 1. 利用CMI方法在高功率激光装置上成功实现了可视化的大口径激光束波前在线精密测量，分析了气流扰动对波前的影响。该测量方法与现有传统的测量方法相比，可以同时测量近场与远场光束的强度与相位信息，并且具有精度高、结构小巧，对环境要求低等优点。 2. 利用CMI方法完成了大口径光学元件复振幅透过率测量。该方法测量过程中只需要记录两幅衍射光斑，抗干扰效果好。由于使用的是单路光束聚焦，无需参考光路，因而CMI方法便于大口径的光学元件测量，并且其能够检测大的位相梯度和高频信息，拥有其它测量方法所不具备的一些优点。 3. 利用CMI方法实现了高重复频率激光器中光学元件热畸变测量。通过CMI算法求得激光器输出光场的相位变化从而反映出光学元件的热畸变。该方法适合于振动条件下光学元件热畸变的实时在线检测，抗干扰效果好，并且能够检测大的相位梯度，解决了高重复频率激光器光学元件热畸变变化量大和振动环境等因素而难以测量的问题。 4. 利用CMI方法实现了装校应力对大口径光学元件面形影响的检测，通过CMI算法获得大口径光学元件面型的相位变化值，从而反映出装校应力对元件面型的影响，该方法解决了传统方法只能通过有限元分析而难以实验测量的难题，对改善光学元件全口径通光区域的面形误差从而提升光束质量输出提供了一种有效的解决方法。 5. 改进算法实现了无透镜的CMI方法。改进后的CMI方法不再需要聚焦透镜，可以有效地减少测量系统的复杂性和入射光束的能量损失，在X射线和电子束成像方面具有潜在的应用。 |
| 英文摘要 | The high-power laser facility for inertial confinement fusion (ICF) is a large-scale and high precision systematic engineering, where a lot of precision and large optical elements uesd in its optical path. A variety of factors during the process of manufacture, installation and operation, such as scratches, surface damage, surface contamination, dust particles and other ‘defects’, surface deformation under improper installation and the effect of gravity, heat accumulation adversely affect the optical properties. Any deviation of the uesd optical element will reduce the quality of the wave-front of the transmission beam. In addition, the laser beam emits from the seed light source then propagates several hundred meters and finally reaches the target chamber. In this process, environmental changes from air flow, temperature will also impact the quality of the laser beam. All of these factors decrease of the quality of the beam and make the focal spot which irradiated to the capsule unable to meet the design specifications. In actual high-power laser devices, a variety of techniques are adopted to control and correct wave-front aberration, but only exactly know the shape, extent and location of the wave-front aberration it can take effective steps to control and improve the beam quality. Thus measurement of the wave-front of the high-power laser beam is very important. The actual used beam in high-power laser drivers is a pulsed laser, it is difficult to obtain the wave-front information in a relatively short time. In addition, the limited space of the high-power facility practically makes it difficult to use the interference measurement method, because it requires a large and high vibration isolation optical platform and a neat parallel or spherical reference beam. The measuring system is complex and it demands rigorous work environment. The general wave-front measurement for the output beam of high-power solid laser employs a Hartmann wave-front sensor which usually used in the adaptive optics system. However, since the resolution of Hartmann wave-front sensors is limited by its sub-aperture and the number of micro-lens used, the resolution obtained by such measurements is hard to meet the actual demand. Also a large phase gradient is difficult to be measured. Therefore it is necessary to develop a new method for measurement of the wave-front of the high-power laser beam. Coherent modulation imaging (CMI) is a newly developed technique for phase recovery. It developed from the PIE (Ptychography Iterative Engine) method. The laser beam to be measured passes through a random phase plate which having a known phase structure distribution, then a CCD camera record the diffraction pattern. The wave-front distribution of the laser beam can be quickly reconstructed from the recorded diffraction pattern with CMI algorithm. The structure of CMI method only include a random phase plate and a CCD camera, it is very simple and compact. It also has many advantages such as fast convergence, low requirement of the measurement environment and dynamic range, high spatial resolution and accuracy. In this paper, the research is carried out to slove the problems of wave-front measurement in high-power laser drivers based on CMI method, the main contents are as follows: 1. Visualization of accurate online wave-front measurement of large diameter laser beam in high-power laser driver with CMI method was successfully achieved. The disturbance of the wave-front by the airflow was also analyzed. Compared with the existing traditional measurement methods, it can simultaneously measure the intensity and phase information of the near-field and far-field of the beam. It also has advantages of high precision, compact, and low environmental requirements. 2. Measurement of the complex transmittance of large optical elements with CMI method was realized. The measuring process of this method only need record two diffraction patterns, it has good anti-interference performance. Due to the single focused beam used and without the reference beam in the optical path, it convenient for measure large diameter optical elements. It can measure large phase gradient and high frequency information, thus possess some advantages which other measurement methods can not realize. 3. Thermal distortion of optical elements in high repetition rate laser with CMI method was measured. The phase difference to reflect the thermal distortion of optical elements can be obtained with the CMI algorithm. This method is suitable for real-time online monitoring the thermal distortion under the vibration conditions. It has good anti-interference performance and can measure large phase gradient thus solves the difficult problem of measurement of the thermal distortion of optical elements in high repetition rate laser with large distortion and vibration environments. 4. Deformation measurement of the reflect mirror under the alignment with CMI method was realized. With the reconstructed phase change of the surface of the large diameter optical element, the surface influenced by the assembling force can be measured. This method solves the problem that the traditional method for deformation evaluate only by the finite element analysis and can not be measured by experiments, thus it provides an effective solution to improve the surface shape error of the optical element when a full aperture of light through the area so as to enhance the quality of the output beam. 5. A lens free CMI method was proposed by improved the algorithm. The improved CMI method is no longer need a focusing lens, it can effectively reduce the complexity of the measurement system and the energy loss of the incident beam. It has potential applications in X-ray and electron beam imaging. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15978]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 陶华. 基于相干调制成像的高功率激光光束波前测量方法研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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