非线性共振X射线拉曼散射
Nonlinear resonant X-ray Raman scattering
摘要：
我们报道了在硬X射线范围内观察到的一种新的非线性效应。在用在Fe和Cu金属箔各自的K边缘附近调谐的强X射线脉冲照射Fe和Cu金属箔时，发射出接近入射光子能量两倍的光子。信号随入射强度呈二次方上升，与双光子激发一致。所发射的高能光子的光谱包括随着入射光子能量而分散的多条拉曼线。当达到双K壳层电离阈值时，信号强度显著上升。在这个阈值以上，谱线停止分散，变成能量比单电子跃迁大得多的拉曼谱线，并出现额外的拉曼谱线。我们将这些过程归因于电子相关介导的多电子跃迁，涉及双核空穴激发和各种双电子去激发过程，涉及一个或多个L和M核心空穴的最终状态。
英文摘要：
We report the observation of a novel nonlinear effect in the hard x-ray range. Upon illuminating Fe and Cu metal foils with intense x-ray pulses tuned near their respective K edges, photons at nearly twice the incoming photon energy are emitted. The signal rises quadratically with the incoming intensity, consistent with two-photon excitation. The spectrum of emitted high-energy photons comprises multiple Raman lines that disperse with the incident photon energy. Upon reaching the double K-shell ionization threshold, the signal strength undergoes a marked rise. Above this threshold, the lines cease dispersing, turning into orescence lines with energies much greater than obtainable by single electron transitions, and additional Raman lines appear. We attribute these processes to electron-correlation mediated multielectron transitions involving double-core hole excitation and various two-electron de-excitation processes to a final state involving one or more L and M core-holes.
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