物理学报2017，Vol.66Issue(15)：64-90,27.DOI:10.7498/aps.66.152901
高相干超快电子源研究进展
Recent progress of high-coherence ultrafast electron sources?
摘要
Abstract
Microscopic dynamic process of material structure which determines the inherent property of substance takes place on a molecular and atomic scale. Understanding the underlying mechanisms of the various fundamental processes has always been the goal of chemistry, physics, biology and materials science. With Ahmed Zewail''s pioneering work in the field of femtoscience, the time-resolved electron diffraction, combining the pump-probe and electron diffraction technique, has become an excellent tool with sufficient temporal precision to directly deliver insights into ultrafast phenomena on an atomic level. Central to this method is the ultrashort electron pulses generated from a metal photocathode. However, up to now, owing to the initial size, effective temperature, energy dispersion and inherent coulomb repulsion of electron source, the state-of-the-art transverse coherence of conventional planar cathode photoemission source is still insufficient to resolve the complex chemical and biological organic molecules. Hence, in recent years, many efforts have focused on developing high-coherence ultrashort electron sources. The main methods include minimizing the initial beam size, weakening the space charge, reducing the effective temperature, and matching the photon energy of laser with the work function of cathode material. In this review, we firstly summarize the history and advantages of the electron probe, secondly sketch out the figure of merit of the electron source. And then taking coherence as the main line, we review recent progress in common planar photoemission sources, and discuss the latest development of tip-based electron sources and cold atom electron sources in terms of their generation mechanisms, unique properties and research progress. Finally, the development and future applications of the diffraction technique are prospected. In general, the high-coherence length of photoelectric surface source is often at the expense of the current. The needle source can obtain the highest coherence length, but it is similar to femtosecond single-electron pulse, which must be less than one electron per pulse to eliminate the electron-electron coulomb interaction. Thus, a diffraction pattern can only be formed by accumulating millions of shots. The cold atom electron source, which has a transverse coherence greater than 15 nm and a peak brightness similar to conventional electron source''s, is sufficient for some molecular systems in biochemistry. In short, with the improvement of coherence and the emergence of new electron sources, it is possible to reveal complex organic and inorganic structures, especially the dynamic behaviors of protein, and promote the understanding of nanoscale energy transport, solid-liquid and solid-gas interfacial dynamics and chemical reaction and so on. High-coherence electron sources not only serve in the diffraction experiments, but also play a key role in developing ultrafast electron microscopy, coherent diffraction imaging and ptychography.关键词
时间分辨电子衍射/分子电影/尖端发射源/冷原子电子源Key words
time-resolved electron diffraction/molecular movie/nanotip electron sources/cold atom electron sources引用本文复制引用
罗端,惠丹丹,温文龙,刘蓉,王兴,田进寿..高相干超快电子源研究进展[J].物理学报,2017,66(15):64-90,27.基金项目
国家自然科学基金青年科学基金(批准号:11304374, 61501363和陕西省自然科学基础研究计划项目(批准号:2016JQ6013资助的课题.通信作者. E-mail:wangxing@opt.ac.cn Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant Nos. 11304374, 61501363 and the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No. 2016JQ6013. （）
