利用饱和吸收缩短X射线脉冲宽度
Shortening X-ray Pulse Duration via Saturable Absorption
摘要：
为了缩短X射线脉冲的持续时间，我们提出了一种利用内壳层光电离产生的具有核-空穴空位原子（核-空穴原子）的非线性光学技术。弱库仑屏蔽的核心空穴原子的结果，在光子能量的吸收边以上的减少。通过采用这种现象，称为饱和吸收，我们成功地减少了X射线自由电子激光脉冲（光子能量：9.000 keV，持续时间：6-7 fs，通量：2.0-3.5 $\times$ 10 $^5$ J/cm $^2$）的持续时间$\sim$ 35%。这一发现，核心空穴原子适用于非线性X射线光学是一个重要的垫脚石扩展非线性技术常见的光学波长的硬X射线区域。
英文摘要：
To shorten the duration of x-ray pulses, we present a nonlinear optical technique using atoms with core-hole vacancies (core-hole atoms) generated by inner-shell photoionization. The weak Coulomb screening in the core-hole atoms results in decreased absorption at photon energies immediately above the absorption edge. By employing this phenomenon, referred to as saturable absorption, we successfully reduce the duration of x-ray free-electron laser pulses (photon energy: 9.000 keV, duration: 6-7 fs, fluence: 2.0-3.5$\times$10$^5$ J/cm$^2$) by $\sim$35%. This finding that core-hole atoms are applicable to nonlinear x-ray optics is an essential stepping stone for extending nonlinear technologies commonplace at optical wavelengths to the hard x-ray region.
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