Observation of femtosecond X-ray interactions with matter using an X-ray-X-ray pump-probe scheme
Observation of femtosecond X-ray interactions with matter using an X-ray-X-ray pump-probe scheme
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DOI：
10.1073/pnas.1516426113
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发表时间：
2016-02-09
影响因子：
11.1
通讯作者：
Yabashi, Makina
中科院分区：
文献类型：
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作者：
Inoue, Ichiro;Inubushi, Yuichi;Yabashi, Makina
非晶样品的X射线结构测定的分辨率已被限制在几十纳米，因为增强分辨率所需的深X射线照射会对样品造成辐射损伤。然而，理论研究预测，飞秒（fs）的X射线自由电子激光（XFEL）脉冲的持续时间使其有可能在X射线损伤过程开始之前记录散射信号;因此，可以使用超过常规辐射剂量限制的超强X射线束。在这里，我们验证了这种情况下，直接观察飞秒X射线损伤过程中的钻石照射非常强烈（类似于10（19）W/cm（2））的XFEL脉冲。在这项研究中开发了一种X射线泵浦-探测衍射方案;使用时间间隔从亚fs到80 fs的紧密聚焦的双5 fs XFEL脉冲来激发（即，泵送）金刚石并表征（即，通过布拉格反射探测）晶体结构的时间变化。结果发现，在双脉冲间隔较短的情况下，泵浦和探测衍射强度几乎保持不变，而在泵浦脉冲照射后20 fs后，由于X射线引起的原子位移，探测衍射强度下降。这一结果表明，亚10-fs的XFEL脉冲使无损结构测定的传导，并支持的理论预测的有效性超强X射线物质相互作用。X射线泵浦-探测方案将有效地用于理解超强X射线-物质相互作用，这将极大地促进先进的XFEL应用，如单分子的原子结构测定和产生具有高能量密度的奇异物质。
Resolution in the X-ray structure determination of noncrystalline samples has been limited to several tens of nanometers, because deep X-ray irradiation required for enhanced resolution causes radiation damage to samples. However, theoretical studies predict that the femtosecond (fs) durations of X-ray free-electron laser (XFEL) pulses make it possible to record scattering signals before the initiation of X-ray damage processes; thus, an ultraintense X-ray beam can be used beyond the conventional limit of radiation dose. Here, we verify this scenario by directly observing femtosecond X-ray damage processes in diamond irradiated with extraordinarily intense (similar to 10(19) W/cm(2)) XFEL pulses. An X-ray pump-probe diffraction scheme was developed in this study; tightly focused double-5-fs XFEL pulses with time separations ranging from sub-fs to 80 fs were used to excite (i.e., pump) the diamond and characterize (i.e., probe) the temporal changes of the crystalline structures through Bragg reflection. It was found that the pump and probe diffraction intensities remain almost constant for shorter time separations of the double pulse, whereas the probe diffraction intensities decreased after 20 fs following pump pulse irradiation due to the X-ray-induced atomic displacement. This result indicates that sub-10-fs XFEL pulses enable conductions of damageless structural determinations and supports the validity of the theoretical predictions of ultraintense X-ray-matter interactions. The X-ray pump-probe scheme demonstrated here would be effective for understanding ultraintense X-ray-matter interactions, which will greatly stimulate advanced XFEL applications, such as atomic structure determination of a single molecule and generation of exotic matters with high energy densities.