X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics
X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics
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DOI：
10.1103/physrevlett.120.243902
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发表时间：
2018-06-12
影响因子：
8.6
通讯作者：
Mukamel, Shaul
中科院分区：
文献类型：
--
作者：
Rouxel, Jeremy R.;Kowalewski, Markus;Mukamel, Shaul
基态分子的 X 射线衍射产生其电荷密度的图像，因此时间分辨 X 射线衍射可以监测原子核的运动。然而，由于核心电子的压倒性背景贡献，用常规衍射技术几乎无法监测光激发时激发价电子的密度变化。我们提出了一种由新型自由电子激光源实现的非线性 X 射线技术，该技术提供了价电子激发的空间电子密度图像。该技术使用可见光泵和宽带 X 射线衍射脉冲进行和频生成，产生跃迁电荷密度的快照，代表光学激发时的电子密度变化。该技术通过对供体或受体取代的二苯乙烯中光诱导电子动力学的跃迁电荷密度成像的从头模拟来说明。
X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved x-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear x-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband x-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor or acceptor substituted stilbene.