| 题名 | 相干衍射成像在激光驱动器中的应用研究 |
| 作者 | 潘兴臣 |
| 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 | 相干衍射成像 相位恢复 迭代算法 相位测量 |
| 其他题名 | Research on Coherent Diffraction Imaging Based Measurement Techniques for Laser Driver |
| 中文摘要 | 作为目前世界上最复杂的一类激光系统，高功率激光驱动器具有庞大的体积、复杂的机械结构和精密的测控反馈系统，并且包含大量不同尺寸不同特性的光学组件，为满足激光惯性约束核聚变对高功率激光驱动器输出能量、峰值功率以及焦斑尺寸的严格要求，不仅需要精密的光学元件检测手段，还需要一套完善的波前诊断和反馈控制系统，目前最常用的光学元件检测方法是激光干涉仪，它可以实现对不同口径光学元件的高精度测量，但由于采用干涉原理，结构比较复杂，对环境稳定性要求比较高，只能用于光学元件的离线检测，并且对一些特殊光学元件的检测还有一定局限性；直接成像法和哈特曼波前传感器是目前高功率激光驱动器光束近远场强度测量和近场相位测量的最主要方法，直接成像法需要一套显微成像系统，光路校准较为复杂，放大倍率和像面位置的不确定性会带来焦斑尺寸的测量误差，而哈特曼传感器由于其分辨率受限于微透镜阵列的加工能力，相位信息的描述能力有限，只能探测基频相位变化，对较大相位梯度的测量具有一定局限性，因此高功率激光驱动器中现有光学元件检测和波前在线诊断方法都面临一定的局限性，需要探索研究新型的波前测量方法，改善现有测量方案的不足，提升对光学元件的测量能力并完善波前在线诊断方案。 相干衍射成像(CDI，Coherent Diffractive Imaging)是一类利用衍射光斑通过迭代计算重建波前信息的相位恢复技术，由于光路结构简单且基于衍射过程，理论上能够达到的精度为衍射极限，并且可以同时提供波前振幅和相位信息的数值解，理论上可以用于解决驱动器面临的光学元件检测和波前在线诊断问题，但目前传统CDI算法，如GS (Gerchberg-Saxton)算法，常面临收敛性问题，只局限于驱动器系统静态像差的校准和特殊条件下的光学元件检测，如果能够解决其收敛性问题，CDI算法在测量领域将会具有显著优势，因此从提高收敛性的角度出发，首先对基于照明光扫描的多光斑PIE(Ptychographic Iterative Engine)算法进行了研究，分析误差来源对重建过程的影响，并提出相应改进算法，虽然PIE算法可以用于测量大口径特殊元件的检测，但并不能解决驱动器中单脉冲光束的在线诊断问题，因此又着重研究了基于相干调制成像的CMI(Coherent Modulation Imaging)算法，完成装置集成后，具有收敛速度快、结构紧凑、可用于光学元件检测及脉冲在线诊断等特点，适用性非常广泛，可成为解决驱动器日常运行中面临的测量和诊断问题的新方法，具有良好的实际应用基础。在硕士期间建立的PIE算法基本概念的基础上，加深和完善对PIE基本算法的系统性研究，同时在此基础上展开CMI算法的理论和应用研究，解决集成化的关键问题，完成波前测量仪的仪器化和应用性研究，为解决驱动器测量问题提供新的方法，主要创新性内容包括以下几个方面： 1、 提出基于光栅分光法的单次曝光PIE算法，克服了PIE算法需要一定数据记录时间的缺点，只需要单幅光斑就可以通过PIE算法进行重建，为单次曝光测量提供了很好的解决思路。 2、 提出部分饱和衍射光斑的改进PIE算法，克服了光斑信息丢失问题的同时，改善PIE算法的重建精度和抗噪能力。 3、 理论上解释了CMI算法快速收敛的原因，将CMI算法完全等效为最快梯度下降法，其收敛性得到解释，同时由于相位板的存在，完全消除了孪生像等对CMI收敛性的影响，使得CMI算法具有较快的收敛速度。 4、 提出了基于双次曝光的弱相位物体成像增强方法，能够通过两幅光斑线性组合得到相位增强N倍时的衍射光斑，继而得到相位增强N倍的物体像。 5、 解决了CMI单次曝光集成化中的关键问题，包括关键元器件设计标定、角度校准算法及对应的控制软件等。针对不同CCD和待测波长，完成三台基于CMI算法的波前测量装置，WFS-GX6600、WFS-Lm11059和WFS-F421B。 6、 完成对基于WFS-GX6600的光学元件检测装置的精度标定、设备溯源研究，在光学元件测量方面，基本达到一级干涉仪标准。 7、 利用WFS-Lm11059完成驱动器中波前在线测量初步验证工作，可以实现对高功率激光驱动器近场强度、相位和远场强度的在线同时测量。 |
| 英文摘要 | As the most complex laser system in the word, high power laser system has huge dimensions, complex mechanical structure and precise diagnostic and feedback system, as well as large amounts of large-scale optical elements. In order to satisfy the requirements on laser energy, peak power and size of focal-spot for inertial confinement fusion (ICF), not only the precious optical inspection but also well-established wave-front diagnostic and feed-back control system are demanded. Interferometer is the most commonly used technology for high accuracy measurement of optical elements with different dimensions. However, due to the principle of interference, interferometer has complex structure and high demands for environment stability, off-line optical elements measurement is the most appropriate applications for high power laser system, but it still to be restrictive for special optical elements with large phase diversity. Direct imaging and Shack-Hartmann sensor are the primary methods in high power laser systems for far-field intensity and near-field phase and intensity measurements. Considering the difficulty of alignment to determine magnification ratio and the position of image plane, measurement error is unavoidable for focal-spot diagnostic with direct imaging. Shack-Hartmann sensor could provide fast phase measurement with compact structure, but its known that the resolution is limited by the manufacture ability of micro lens array and it has finite description capability of wave-front especially for large phase distortion, its only suitable for basic frequency measurement with limited spatial resolution. In order to break recent limitations on optical metrology and wave-front diagnostic in high power laser facilities, it’s essential to develop new measurement technics to improve performance of optical measurement and on-line wave-front diagnostic. Based on iterative engine with intensity patterns, coherent diffractive imaging (CDI) could retrieve phase information with simple setup and diffraction limited resolution in theory. Considering its distinctive capability to provide complete numerical description about phase and modulation, it has the potential applications in the field of optical measurement and wave-front diagnostic. However, when it comes to traditional CDI algorithms, such as GS (Gerchberg-Saxton) algorithm, it’s difficult to always guarantee convergence for sophisticated wave field. As a result, it’s only used for static calibration of phase distortions in laser driver and optical element measurement in special condition. However, if the problem of convergence could be resolved properly, CDI could be a promising technique for optical measurement and on-line wave-front diagnostic. From the problem-solving point of view, start the research from the algorithm of PIE (Ptychographic Iterative Engine) based on probe shifting and analysis the relationship between parameter errors and iterative process. And during that process, improved algorithms are proposed at the same time. PIE is not suitable for on-line wave diagnostic of single laser pulse, although it could be a promising solution for the measurement of large scale optical elements. Consequently, we pay more attention to the algorithm CMI (Coherent Modulation Imaging), which has compact structure after integration, rapid convergence speed and the potential capabilities of optical element measurement and single-shot wave-front diagnostic. It could be a practical and promising technique to solve the measurement problems in laser driver with extended applicability and application fundament. Based on the understanding of PIE during Master degree candidate, improve and perfect the systematic research on PIE and start the research on theory and application of CMI. In order to provide a novel wave-front measurement technique, solve the key problem of instrument integration based on CMI and finish corresponding application research work. The mainly work includes: 1. Propose single-shot PIE algorithm based on grating and overcome the the time consuming disadvantage during data recording process of PIE. It provides a new idea for single-shot measurement with PIE. 2. Propose a modified PIE algorithm with partially saturated diffraction patterns, overcome the problem of information missing while enhancing the final resolution at the same time. 3. Explan the reson of fast convergence speed of CMI based on Steepest-Descent method. Due to the elimination of twin image on CMI, fast convergence speed could available with random phase plate. 4. Propose dual-shot PIE algorithm with enhanced image of weakly scattering object. It could be possible by synthetising diffraction pattern of enhanced phase image by N times with prior known two intensity patterns. 5. Solve the key integration problem of single-shot wave-front measurement based on CMI, including the design of key optical element, angle calibration algorithm and corresponding control software. Develop three integrated instruments for different wavelength, and named as WFS-GX6600, WFS-Lm11059, WFS-F421B. 6. Complete the traceable resolution calibration of WFS-GX6600 by comparing with Zygo interferometor and mainly reach the demanding of first order interferometor. 7. Complete the preliminary application research of on-line wave-front measurement in high power laser system with WFS-Lm11059 and it could accomplish the measurement of near-field intensity, near-field phase and far-field intensity at the same time. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15990]  |
| 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 | 潘兴臣. 相干衍射成像在激光驱动器中的应用研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
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