随着能量输出能力的不断提升，高功率激光驱动器运行对光学元件的性能和打靶光束的质量都有了更高要求。传统测量仪器结构复杂、精度有限，难以满足实验需求。朱健强课题组将计算成像技术引入到高功率激光驱动器的参数测量中，精确测量大口径光学元件的形貌、应力分布、热畸变等特征，脉冲光束的时间、空间、近远场分布等参量，以及激光与物质相互作用的过程；进一步发展相干衍射成像（CDI）技术，开发出单次曝光三维PIE（ptychography iterative engine）技术、多模态相干调制成像（CMI）技术、分束编码成像技术等，建立了相干衍射成像技术的解析模型，在数学上分析了CDI技术解的唯一性。本文主要综述了课题组在惯性约束聚变中计算光学成像技术应用方面的研究进展。

在迭代重建光学传递函数（OTF）测量法中，采集了多幅图像并进行更新计算，因而其具有抗噪声鲁棒性强和抗混叠等优点。然而，在图像采集过程中，不可避免的振动会引起多幅图像之间存在微小的相对平移，进而导致迭代计算次数增加和调制传递函数（MTF）测量结果准确性下降。该测量方法采集到的图像为随机排布的多个点扩散函数（PSF），多幅图像之间无法应用相位相关法来计算相对平移。鉴于此，提出了一种基于相位传递函数（PTF）的多幅图像相对平移校准方法。将每一幅图像单次计算的PTF分别减去第一幅图像单次计算的PTF，根据该差值校准多幅图像之间的相对平移。数值仿真和实验研究结果表明，所提方法的计算精度与图像相对平移的大小无关，至多能够将迭代次数减少80%，并将MTF测量的均方误差降低1~2个数量级。

提出一种大倾角照明条件下的高精度PIE(ptychographic iterative engine)迭代重建算法。该算法用小角度照明的透射光代替大角度照明的透射光,通过修正角谱传递函数,得到适应大角度迭代的光场传输公式。在非傍轴条件下,该算法能够避免样品面上相位分布欠采样的问题,同时精确计算衍射面上的衍射光斑,为单次曝光PIE成像的进一步发展和实际应用解决了最为关键的技术难题。

Ptychography是近些年快速发展起来的一种新型相位恢复技术,通过对待测样品以小于照明光直径的步长扫描后,利用迭代计算可以重建出照明光和样品复振幅分布,是一种理论分辨率为衍射极限的非透镜相位成像技术。虽然其提出初期受限于基本假定条件,但近些年随着相关研究的跟进,人们对Ptychography算法特性的理解逐渐深入,算法也日趋成熟,在可见光、X射线和电子束等领域已被广泛应用于相位成像、波前诊断和光学计量,因此针对影响重建过程和精度的关键因素,如模态多样化、扫描误差、光斑误差、距离误差、样品厚度不可忽略等进行了总结,并讨论了针对上述问题的关键技术进展。

As a newly developed lensless imaging technique, PIE (ptychographical iterative engine) does not only maintain the simplicity and convenience of the equipment of traditional coherent diffraction imaging (CDI) methods, but also overcomes the drawbacks such as restricted field of view and slow convergence. With the extensible imaging field, better convergence speed and higher immunization capability to noise, PIE is widely researched and used in optical, X-ray and electron beam imaging fields. PIE is a new method which is possible to replace the current phase imaging methods. The background, development, applications, problems and developing trend of the PIE method are introduced.

Coherent modulation imaging (CMI) based algorithm has been employed for on- shot laser beam diagnostics in high power laser facility and off- line measurement of large- scale optic element. A single- shot intensity measurement is sufficient for wave-front reconstruction after the random phase plate has been accurately pre- characterized, and the iteration process can be finished in 30 seconds with the acceleration of graphics processing unit (GPU) device. Furthermore, a compact structure is also available after combining CCD and phase plate together, which can be placed almost anywhere of high power laser facilities. Series of experiments have been finished for focal-spot prediction, measurement of large-scale continuous phase plate, and on-shot wave-front reconstruction of seed pulse in our high power laser facility with amplifiers turned off. The flexibility of CMI for focal- spot prediction, on- shot wave- front diagnostic and off- line measurement of optic elements has been demonstrated for its characteristic. It has significant influence on the development of high power laser facilities as a new method for wave-front measurement and diagnostics.

When high-power solid laser working in high repetition rate, the laser output wave-front changes due to the thermal distortion, which is caused by the gain medium under the heat deposition. Therefore, the coherent modulation imaging technology is used to realize the measurement of the laser output wave-front from one frame of diffraction intensity recorded. The phases of thermal distortion of the optical element are obtained when the amplifier working in 1, 5, 7 Hz frequency. Experimental results show that thermal distortion effect is significantly increased, the heat is concentrated toward the center region and the phase change increases as the working frequency increases.

高功率固体激光器工作在高重复频率时，增益介质因热量的沉积而发生热畸变，导致激光输出波前发生变化。为此，利用相干调制成像技术通过记录单幅衍射光斑实现输出光场的波前测量，获得了放大器工作在1,5,7 Hz频率时光学元件的热畸变相位。实验结果显示，随着工作频率增大，热量向中心区域集中，热沉积效应明显增加了波前变化。

作为一种新近发展的无透镜成像技术，PIE(ptychographical iterative engine)不但保持了传统相干衍射成像方法装置简单、使用方便等优点，克服了视场受限和收敛速度慢等缺点，还具有成像范围可扩展、收敛速度快、抗噪声能力强等优势，在光学、X射线和电子束等领域得到了广泛关注并开展了大量研究，是一种有可能在大范围内替代现有相位成像技术的新方法。主要介绍了PIE方法的技术背景、技术现状、相关应用及面临的问题和可能的发展方向。

基于相位调制的迭代算法被用于高功率激光驱动器的波前在线测量和大口径光学元件的离线检测，该算法只需要单幅衍射光斑和一块分布已知的随机相位板，利用图形处理器(GPU)硬件加速后可在30 s 以内完成迭代计算，并且集成后结构紧凑，基本可放置于高功率激光驱动器的任意位置。基于该方法完成了焦斑预测和对比实验，在现有高功率激光驱动器中对种子光的波前分布进行了在线测量，同时实现连续相位板(CPP)的离线检测。相关实验表明，该算法能够用于解决高功率激光驱动器中焦斑预测、波前在线恢复和大口径光学元器件检测的问题，具有广泛的适用性，适用于高功率激光驱动器的波前测控系统以及作为元件检测的新方法，对于激光驱动器的发展具有十分重要的实际意义。