Spence J C H, Weierstall U, Howells M
Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA.
Philos Trans A Math Phys Eng Sci. 2002 May 15;360(1794):875-95. doi: 10.1098/rsta.2001.0972.
Thomas Young's quantitative analysis of interference effects provided the confidence needed to revive the wave theory of light, and firmly established the concept of phase in optics. Phase plays a similarly fundamental role in matter-wave interferometry, for which the field-emission electron microscope provides ideal instrumentation. The wave-particle duality is vividly demonstrated by experimental 'Young's fringes' using coherent electron beams under conditions in which the flight time is less than the time between particle emission. A brief historical review is given of electron interferometry and holography, including the Aharonov-Bohm effect and the electron Sagnac interferometer. The simultaneous development of phase-contrast imaging at subnanometre spatial resolution has greatly deepened our understanding of atomic processes in biology, materials science and condensed-matter physics, while electron holography has become a routine tool for the mapping of electrostatic and magnetic fields in materials on a nanometre scale. The encoding of phase information in scattered farfield intensities is discussed, and non-interferometric, non-crystallographic methods for phase retrieval are reviewed in relationship to electron holography. Examples of phase measurement and diffraction-limited imaging using the hybrid input-output iterative algorithm are given, including simulations for soft X-ray imaging, and new experimental results for coherent electron and visible-light scattering. Image reconstruction is demonstrated from experimental electron and visible-light Fraunhofer diffraction patterns. The prospects this provides for lensless imaging using particles for which no lenses exist (such as neutrons, condensates, coherent atom beams and X-rays) are discussed. These new interactions can be expected to provide new information, perhaps, for example, in biology, with the advantage of less damage to samples.
托马斯·杨对干涉效应的定量分析为复兴光的波动理论提供了所需的信心，并在光学领域牢固地确立了相位的概念。相位在物质波干涉测量中也起着同样重要的基础作用，场发射电子显微镜为其提供了理想的仪器设备。在飞行时间小于粒子发射间隔时间的条件下，利用相干电子束进行的实验性“杨氏条纹”生动地展示了波粒二象性。本文简要回顾了电子干涉测量和全息术的历史，包括阿哈罗诺夫 - 玻姆效应和电子萨格纳克干涉仪。亚纳米空间分辨率下相衬成像的同步发展极大地加深了我们对生物学、材料科学和凝聚态物理中原子过程的理解，而电子全息术已成为在纳米尺度上绘制材料中静电和磁场的常规工具。讨论了散射远场强度中相位信息的编码，并结合电子全息术回顾了用于相位恢复的非干涉、非晶体学方法。给出了使用混合输入 - 输出迭代算法进行相位测量和衍射极限成像的示例，包括软X射线成像的模拟以及相干电子和可见光散射的新实验结果。从实验电子和可见光夫琅禾费衍射图样演示了图像重建。讨论了这为使用不存在透镜的粒子（如中子、凝聚态、相干原子束和X射线）进行无透镜成像提供的前景。这些新的相互作用有望提供新的信息，例如在生物学中，可能具有对样品损伤较小的优点。
