X‐ray free‐electron lasers (X‐FELs) present new opportunities to study ultrafast lattice dynamics in complex materials. While the unprecedented source brilliance enables high fidelity measurement of structural dynamics, it also raises experimental challenges related to the understanding and control of beam‐induced irreversible structural changes in samples that can ultimately impact the interpretation of experimental results. This is also important for designing reliable high performance X‐ray optical components. In this work, X‐FEL beam‐induced lattice alterations are investigated by measuring the shot‐to‐shot evolution of near‐Bragg coherent scattering from a single crystalline germanium sample. It is shown that X‐ray photon correlation analysis of sequential speckle patterns measurements can be used to monitor the nature and extent of lattice rearrangements. Abrupt, irreversible changes are observed following intermittent high‐fluence monochromatic X‐ray pulses, thus revealing the existence of a threshold response to X‐FEL pulse intensity.

中文翻译：

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散斑相关作为X射线自由电子激光诱导的晶格变形的监测器

X射线自由电子激光器（X-FEL）提供了研究复杂材料中超快晶格动力学的新机会。尽管空前的光彩可以对结构动力学进行高保真度测量，但同时也带来了与理解和控制光束中不可逆的结构变化有关的实验挑战，这些变化最终会影响实验结果的解释。这对于设计可靠的高性能X射线光学组件也很重要。在这项工作中，通过测量单晶锗样品中近布拉格相干散射的逐次发射演变，研究了X-FEL束引起的晶格变化。结果表明，连续散斑图样测量的X射线光子相关分析可用于监视晶格重排的性质和程度。在间歇性高通量单色X射线脉冲后观察到突然的，不可逆的变化，从而表明存在对X-FEL脉冲强度的阈值响应。