ABSTRACT

A fascinating way of generating speckle patterns is by interfering the weak fields scattered by a disordered sample with the intense trans-illuminating beam. The resulting intensity fluctuations are known as Heterodyne Near Field Speckles. Thanks to the self-referencing layout, the intensity distribution allows direct assessment of the electric fields, thus preserving both amplitude and phase information. Originally observed with visible laser light, during the last years Heterodyne Near Field Speckles have been extended to partially coherent radiation and to X-ray beams. We give in this review a uniform argumentation of Heterodyne Near Field Speckles based on Fourier Optics, valid with both coherent and partially coherent illumination. Emphasis is given to the speckle size, a fundamental property of any speckle field and a basis for earlier and state-of-the-art development of the technique. We review the applications of Heterodyne Near Field Speckles in the fields of particle sizing, velocimetry, coherence measurements, X-ray wavefront sensing and X-ray phase-contrast imaging and tomography. Throughout the discussion, we also emphasize the common aspects shared with many different research areas, such as astronomical observations, holography and TEM imaging, thus evidencing the encompassing nature of the underlying physical principles.

摘要

产生斑点图案的一种有趣方式是通过用强透射照明光束干扰由无序样品散射的弱场。由此产生的强度波动被称为外差近场斑点。借助自参考布局，强度分布可以直接评估电场，从而保留幅度和相位信息。在最初几年中，最初是用可见激光观察到的，而外差近场散斑已扩展到部分相干辐射和X射线束。在本文中，我们对基于傅立叶光学的外差近场散斑给出统一的论证，对相干和部分相干照明均有效。重点是斑点大小，任何散斑场的基本特性，以及该技术的早期和最新发展的基础。我们回顾了杂散近场散斑在粒子尺寸，测速，相干测量，X射线波前感测以及X射线相衬成像和层析成像等领域的应用。在整个讨论中，我们还强调了与许多不同研究领域（如天文观测，全息照相和TEM成像）共享的共同方面，从而证明了基本物理原理的包容性。