超快电子损伤对单粒子X射线成像实验的影响
Impact of ultrafast electronic damage in single particle x-ray imaging experiments
摘要：
在单粒子相干X射线衍射成像实验中，在X射线自由电子激光器（XFEL）上进行，样品暴露于强X射线脉冲以获得单次衍射图案。高强度在系统中诱导飞秒时间尺度上的电子动力学，这可以降低所获得的衍射图案的对比度并增加各向同性背景。我们通过对暴露于具有不同参数的X射线脉冲的生物样品进行模拟来量化来自超快电子损伤的衍射图案的退化。我们发现，只有当几乎所有的电子都被从它们的母原子中移除时，对比度才大大降低，背景才相当强。这种情况发生在比目前可用的XFEL源提供的通量大至少一个数量级的情况下。
英文摘要：
In single particle coherent x-ray diffraction imaging experiments, performed at x-ray free-electron lasers (XFELs), samples are exposed to intense x-ray pulses to obtain single-shot diffraction patterns. The high intensity induces electronic dynamics on the femtosecond time scale in the system, which can reduce the contrast of the obtained diffraction patterns and adds an isotropic background. We quantify the degradation of the diffraction pattern from ultrafast electronic damage by performing simulations on a biological sample exposed to x-ray pulses with different parameters. We find that the contrast is substantially reduced and the background is considerably strong only if almost all electrons are removed from their parent atoms. This happens at fluences of at least one order of magnitude larger than provided at currently available XFEL sources.
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