Shen X, Li R K, Lundström U, Lane T J, Reid A H, Weathersby S P, Wang X J
SLAC National Accelerator Laboratory,2575 Sand Hill Road, Menlo Park, CA 94025, USA.
SLAC National Accelerator Laboratory,2575 Sand Hill Road, Menlo Park, CA 94025, USA.
Ultramicroscopy. 2018 Jan;184(Pt A):172-176. doi: 10.1016/j.ultramic.2017.08.019. Epub 2017 Sep 1.
To understand and control the basic functions of physical, chemical and biological processes from micron to nano-meter scale, an instrument capable of visualizing transient structural changes of inhomogeneous materials with atomic spatial and temporal resolutions, is required. One such technique is femtosecond electron microdiffraction, in which a short electron pulse with femtosecond-scale duration is focused into a micron-scale spot and used to obtain diffraction images to resolve ultrafast structural dynamics over a localized crystalline domain. In this letter, we report the experimental demonstration of time-resolved mega-electron-volt electron microdiffraction which achieves a 5 μm root-mean-square (rms) beam size on the sample and a 110 fs rms temporal resolution. Using pulses of 10k electrons at 4.2 MeV energy with a normalized emittance 3 nm-rad, we obtained high quality diffraction from a single 10 μm paraffin (CH) crystal. The phonon softening mode in optical-pumped polycrystalline Bi was also time-resolved, demonstrating the temporal resolution limits of the instrument. This new characterization capability will open many research opportunities in material and biological sciences.
为了理解和控制从微米到纳米尺度的物理、化学和生物过程的基本功能，需要一种能够以原子空间和时间分辨率可视化非均匀材料瞬态结构变化的仪器。飞秒电子微衍射就是这样一种技术，其中持续时间为飞秒级的短电子脉冲被聚焦到微米级光斑中，并用于获取衍射图像，以解析局部晶域上的超快结构动力学。在本信函中，我们报告了时间分辨兆电子伏特电子微衍射的实验演示，该技术在样品上实现了5μm的均方根（rms）束斑尺寸和110 fs的均方根时间分辨率。使用能量为4.2 MeV、归一化发射度为3 nm-rad的10k个电子脉冲，我们从单个10μm的石蜡（CH）晶体中获得了高质量的衍射图样。光泵浦多晶Bi中的声子软化模式也得到了时间分辨，展示了该仪器的时间分辨率极限。这种新的表征能力将为材料和生物科学领域带来许多研究机会。
