标题： 高重复率自种子X射线自由电子激光器中亚毫电子伏非弹性X射线散射的新机遇 显示英文标题

标题： Novel opportunities for sub-meV inelastic X-ray scattering at high-repetition rate self-seeded X-ray free-electron lasers

摘要： 非弹性X射线散射（IXS）是研究凝聚态物质平衡动力学的重要工具。 最近提出的一种用于超高分辨率IXS（UHRIX）的新光谱仪分别实现了0.6~meV和0.25~nm$^{-1}$的光谱和动量转移分辨率。 然而，为了弥合高频率和低频率探测器在能量-动量空间之间的差距，还需要进一步提高到0.1~meV和0.02~nm$^{-1}$。 我们表明，通过进一步优化X射线光学器件并增加入射X射线脉冲的光谱通量可以实现这一目标。 UHRIX在5至10 keV的能量范围内表现最佳，在欧洲XFEL的SASE-2束线上，自种子和波荡器调制的组合有望使平均光谱通量比饱和状态下的标准SASE脉冲提高百倍，或比基于存储环的辐射源多三个数量级。 波动光学传播显示，在$7\times 10^{12}$~ph/s的范围内，可以在样品上实现$90$-$\mu$eV带宽。 这将为IXS的动力学研究提供独特的新的可能性。 显示英文摘要

摘要： Inelastic X-ray scattering (IXS) is an important tool for studies of equilibrium dynamics in condensed matter. A new spectrometer recently proposed for ultra-high-resolution IXS (UHRIX) has achieved 0.6~meV and 0.25~nm$^{-1}$ spectral and momentum transfer resolutions, respectively. However, further improvements down to 0.1~meV and 0.02~nm$^{-1}$ are required to close the gap in energy-momentum space between high and low frequency probes. We show that this goal can be achieved by further optimizing the X-ray optics and by increasing the spectral flux of the incident X-ray pulses. UHRIX performs best at energies from 5 to 10 keV, where a combination of self-seeding and undulator tapering at the SASE-2 beamline of the European XFEL promises up to a hundred-fold increase in average spectral flux compared with nominal SASE pulses at saturation, or three orders of magnitude more than possible with storage-ring based radiation sources. Wave-optics propagation shows that about $7\times 10^{12}$~ph/s in a $90$-$\mu$eV bandwidth can be achieved on the sample. This will provide unique new possibilities for dynamics studies by IXS.