Colombo Alessandro, Zimmermann Julian, Langbehn Bruno, Möller Thomas, Peltz Christian, Sander Katharina, Kruse Björn, Tümmler Paul, Barke Ingo, Rupp Daniela, Fennel Thomas
Laboratory for Solid State Physics, ETH Zürich, 8093 Zürich, Switzerland.
Institute for Optics and Atomic Physics, Technical University Berlin, 10623 Berlin, Germany.
J Appl Crystallogr. 2022 Sep 14;55(Pt 5):1232-1246. doi: 10.1107/S1600576722008068. eCollection 2022 Oct 1.
Single-shot coherent diffraction imaging (CDI) is a powerful approach to characterize the structure and dynamics of isolated nanoscale objects such as single viruses, aerosols, nanocrystals and droplets. Using X-ray wavelengths, the diffraction images in CDI experiments usually cover only small scattering angles of a few degrees. These small-angle patterns represent the magnitude of the Fourier transform of the 2D projection of the sample's electron density, which can be reconstructed efficiently but lacks any depth information. In cases where the diffracted signal can be measured up to scattering angles exceeding ∼10°, in the wide-angle regime, some 3D morphological information of the target is contained in a single-shot diffraction pattern. However, the extraction of the 3D structural information is no longer straightforward and defines the key challenge in wide-angle CDI. So far, the most convenient approach relies on iterative forward fitting of the scattering pattern using scattering simulations. Here the Scatman is presented, an approximate and fast numerical tool for the simulation and iterative fitting of wide-angle scattering images of isolated samples. Furthermore, the open-source software implementation of the Scatman algorithm, , is published and described in detail. The Scatman approach, which has already been applied in previous work for forward-fitting-based shape retrieval, adopts the multi-slice Fourier transform method. The effects of optical properties are partially included, yielding quantitative results for small, isolated and weakly interacting samples. is capable of computing wide-angle scattering patterns in a few milliseconds even on consumer-level computing hardware, potentially enabling new data analysis schemes for wide-angle coherent diffraction experiments.
单次相干衍射成像（CDI）是一种用于表征孤立纳米级物体（如单个病毒、气溶胶、纳米晶体和液滴）的结构和动力学的强大方法。利用X射线波长，CDI实验中的衍射图像通常仅覆盖几个度的小散射角。这些小角度图案代表了样品电子密度二维投影的傅里叶变换的幅度，其可以有效地重建，但缺乏任何深度信息。在衍射信号可以测量到超过约10°散射角的情况下，即在广角区域，单次衍射图案中包含了目标的一些三维形态信息。然而，三维结构信息的提取不再直接，这定义了广角CDI中的关键挑战。到目前为止，最方便的方法依赖于使用散射模拟对散射图案进行迭代正向拟合。这里介绍了Scatman，一种用于孤立样品广角散射图像模拟和迭代拟合的近似且快速的数值工具。此外，还详细发布并描述了Scatman算法的开源软件实现。Scatman方法已经在先前基于正向拟合的形状检索工作中得到应用，它采用了多切片傅里叶变换方法。部分包含了光学性质的影响，从而为小的、孤立的和弱相互作用的样品产生定量结果。即使在消费级计算硬件上，Scatman也能够在几毫秒内计算广角散射图案，这可能为广角相干衍射实验带来新的数据分析方案。
