Dark-field X-ray microscopy, DFXM, is a new full-field imaging technique that non-destructively maps the structure and local strain inside deeply embedded crystalline elements in three dimensions. In DFXM an objective lens is placed along the diffracted beam to generate a magnified projection image of the local diffracted volume. In this work, a general formalism based on geometrical optics is provided for the diffraction imaging, valid for any crystallographic space group. This allows the simulation of DFXM images based on micro-mechanical models. Example simulations are presented with the formalism, demonstrating how this may be used to design new experiments or to interpret existing ones. In particular, it is shown how modifications to the experimental design may tailor the reciprocal-space resolution function to map specific components of the deformation-gradient tensor. The formalism supports multi-length-scale experiments, as it enables DFXM to be interfaced with 3D X-ray diffraction. To illustrate the use of the formalism, DFXM images are simulated from different contrast mechanisms on the basis of the strain field around a straight dislocation.

中文翻译：

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在暗场 X 射线显微镜下模拟对比度的几何光学形式

暗场 X 射线显微镜 DFXM 是一种新的全场成像技术，可在三个维度上无损地映射深层嵌入的晶体元素内部的结构和局部应变。在 DFXM 中，物镜沿衍射光束放置，以生成局部衍射体积的放大投影图像。在这项工作中，为衍射成像提供了基于几何光学的一般形式，适用于任何晶体空间群。这允许基于微机械模型模拟 DFXM 图像。示例模拟以形式主义呈现，展示了如何将其用于设计新实验或解释现有实验。特别是，展示了对实验设计的修改如何调整倒易空间分辨率函数以映射变形梯度张量的特定分量。形式主义支持多长度尺度实验，因为它使 DFXM 能够与 3D X 射线衍射接口。为了说明形式主义的使用，基于直位错周围的应变场，从不同的对比机制模拟了 DFXM 图像。