Time dependence of Bragg forward scattering and self-seeding of hard x-ray free-electron lasers
Time dependence of Bragg forward scattering and self-seeding of hard x-ray free-electron lasers
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硬 X 射线自由电子激光器的布拉格前向散射和自播种的时间依赖性
DOI：
10.1103/physrevstab.15.050706
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发表时间：
2012
影响因子：
--
通讯作者：
Y. Shvyd’ko
中科院分区：
文献类型：
--
作者：
R. Lindberg;Y. Shvyd’ko
自由电子激光器 (FEL) 现在可以产生前所未有的亮度的瞬时短高功率 X 射线脉冲，尽管它们的纵向相干性相对较差。通过采用窄带宽 X 射线晶体光学器件可以潜在地改善纵向相干性，在这种情况下，人们还必须了解晶体如何影响时间和空间上的场分布。我们将 X 射线衍射的动力学理论框架为一组耦合波，以便导出来自时间短入射脉冲的布拉格散射的时空响应的解析表达式。我们计算了反射和前向散射的 X 射线脉冲的轮廓，表明波的时间延迟 $\ensuremath{\tau}$ 通过简单的关系 $\ensuremath{\Delta}x=c\ensuremath{\tau}\mathrm{cot}\ensuremath{\theta}$ 与其横向空间位移 $\ensuremath{\Delta}x$ 相关联，其中$\ensuremath{\theta}$ 是衍射平面的入射掠角。最后，我们应用我们的研究结果来获得与单色种子硬 X 射线 FEL 相关的布拉格前向散射的分析描述。
Free-electron lasers (FELs) can now generate temporally short, high power x-ray pulses of unprecedented brightness, even though their longitudinal coherence is relatively poor. The longitudinal coherence can be potentially improved by employing narrow bandwidth x-ray crystal optics, in which case one must also understand how the crystal affects the field profile in time and space. We frame the dynamical theory of x-ray diffraction as a set of coupled waves in order to derive analytic expressions for the spatiotemporal response of Bragg scattering from temporally short incident pulses. We compute the profiles of both the reflected and forward-scattered x-ray pulses, showing that the time delay of the wave $\ensuremath{\tau}$ is linked to its transverse spatial shift $\ensuremath{\Delta}x$ through the simple relationship $\ensuremath{\Delta}x=c\ensuremath{\tau}\mathrm{cot}\ensuremath{\theta}$, where $\ensuremath{\theta}$ is the grazing angle of incidence to the diffracting planes. Finally, we apply our findings to obtain an analytic description of Bragg forward scattering relevant to monochromatically seed hard x-ray FELs.