相干衍射成像技术是一种无透镜计算成像技术。该技术通过迭代算法求解相位问题, 直接从衍射强度数据重构物体的振幅和相位图像信息, 可获得由照明光源波长和数据记录有效数值孔径决定的衍射极限分辨率。由于相干衍射成像技术不依赖于高质量光学成像元件的使用, 因而适合用于深紫外、X射线以及电子束等诸多很难制作高性能成像器件的辐射源。过去20年来新型光源(冷致电子枪、第三代和第四代同步辐射光源、自由电子激光器)、单粒子计数高灵敏度、宽动态范围面阵检测器的迅猛发展, 也极大地促进了相干衍射成像技术的发展。目前相干衍射成像在材料科学和生物学等热门学科方向上已经显示出了相较传统方法的独特优势, 在部分应用上已经逐渐成为主流技术。文中概略回顾相干衍射成像的发展历史。重点介绍叠层扫描相干衍射成像和相干调制成像这两种快速发展的技术。

Coherent diffraction imaging(CDI) is a lensless computational imaging technique, which reconstructs the amplitude and phase of an object directly from diffraction intensity measurement by solving the phase problem using iterative algorithms. CDI can provide images at the diffraction limit resolution that is only determined by the wavelength of radiation source and the effective numerical aperture of the recorded data. Since CDI has no need for high quality imaging optics, it is suitable for short wavelength radiations such as deep ultraviolet, X-rays, and electron beam, for which imaging optics of high performance are difficult to make. Meanwhile, the past 20 years have seen rapid progress of new type of light sources (cold emission electron guns, 3rd and 4th generation synchrotron X-rays sources, and free-electron lasers), array detectors with single particle sensitivity and broad dynamic range. All those progresses greatly promote the development of CDI. At present, CDI has shown some unique advantages over traditional methods in some study of materials science and biology, and gradually becomes a mainstream technology for certain applications. This paper briefly summarized the history of CDI with a focus on ptychography and coherent modulation imaging.