Improved method for studying the propagation dynamics of ultrafast electron pulses based on mean-field models

We have studied the propagation dynamics of ultrafast electron pulses by using an improved mean-field model, in which the propagation of the electron pulses across the boundary of the acceleration region is explicitly considered. A large decrease in the speed spread of the electron pulses(we called "boundary kick") is observed and properly treated leading to a significant improvement in the simulation accuracy, particularly when the density of electrons is very large. We show that our method is consistent with the simulation by the N-particle method, while others can introduce factorial error.     

Ultrafast Electron Diffraction with Spatiotemporal Resolution of Atomic Motion

Ultrafast electron diffraction （UED） is a rapidly advancing technique capable of recording the atomic-detail structural dynamics in real time. We report the establishment of the first UED system in China. Employing this UED apparatus, both the coherent and the concurrent thermal lattice motions in an aluminium thin-film, trigged by ultrafast laser heating, have been observed. These results demonstrate its ability to directly measure a sub-milli-angstrom lattice spacing change on a sub-picosecond time scale.     

用超快电子衍射技术研究Al薄膜的超快动力学行为

超快电子衍射（UED）技术因其同时具有亚皮秒的时间分辨和亚毫埃的空间分辨能力,成为研究物质瞬态结构变化,特别是研究晶格材料超快动力学的有力工具.应用国内首台自行研制的UED系统,我们实时测量了超快激光脉冲激发下,20 nm金属Al多晶薄膜产生的相干声子和晶格热运动.实验结果显示,在晶格热运动加剧的同时,热应力的作用使晶格产生了相干振荡,并最终膨胀达到新的平衡位置.实验中测得的振荡周期以及晶格上升的温度与理论计算的结果符合较好,展示了UED技术在超快晶格动力学研究方面的广阔应用前景 关键词： 超快电子衍射 相干声子 晶格热运动     

高反射效率高定向性的热解石墨晶体X射线谱仪

基于高定向热解石墨晶体(highly oriented pyrolitic graphite,HOPG)研制了一种新型反射式X射线谱仪.该谱仪具有高反射效率、较高能谱分辨率及相对较宽的能谱测量范围.根据计算,在相同的入射条件下,该谱仪的效率比一般X射线弯晶谱仪高3个量级;谱仪能谱分辨率理论值最高达350;理论探测范围是6.891keV至9.193 keV.我们将该谱仪应用在高功率密度激光与固体靶相互作用的实验中,发现在普通弯晶谱仪无法采到信号的实验条件下,HOPG谱仪依然采集到清晰的Cu K谱线.分析发现在8.048 keV(Cu的Kα光子能量)附近的能谱分辨能力最高达到40 eV,分辨率大于200.     

化学名词审定委员会在京成立

全国自然科学名词审定委员会和中国化学会,于1986年3月25日在北京召开了“化学名词审定委员会”成立会。梁树权任主任委员,梁晓天任副主任委员,王夔、张滂、周同惠、韩德刚、施良和、汪德熙分别担     

稀土元素示踪坡面冲刷侵蚀过程的室内模拟试验研究

为确定坡面侵蚀产沙的时空演变规律,通过沿坡面垂直分段和分层结合布设不同稀土元素,采用室内放水冲刷试验系统,分析了各坡段侵蚀产沙量和侵蚀率变化过程. 结果表明:坡面侵蚀产沙可分为3个阶段:面蚀阶段、沟蚀阶段和沟蚀稳定阶段. 试验结束时,上坡段土壤总侵蚀量为17.527 kg,占坡面总侵蚀量的89.2%,其中La和Eu示踪区的侵蚀量各占坡面总侵蚀量的48.1%和23.8%. La,Eu,Yb,Tb,Ce,Nd和Sm 7个示踪区的累积侵蚀量之比为:1:0.495:0.184:0.177:0.146:0.030:0.074,坡面上段、中段和下段累积侵蚀量之比为:1:0 095:0.040. 试验过程中,上坡段细沟蚀剧烈,中坡段主要以面蚀为主,伴有轻微沟蚀,而下坡段始终以面蚀存在.     

Ultrafast electron diffraction

Ultrafast electron diffraction(UED) technique has proven to be an innovative tool for providing new insights in lattice dynamics with unprecedented temporal and spatial sensitivities. In this article, we give a brief introduction of this technique using the proposed UED station in the Synergetic Extreme Condition User Facility(SECUF) as a prototype. We briefly discussed UED's functionality, working principle, design consideration, and main components. We also briefly reviewed several pioneer works with UED to study structure-function correlations in several research areas. With these efforts,we endeavor to raise the awareness of this tool among those researchers, who may not yet have realized the emerging opportunities offered by this technique.     

超快电子衍射系统的时间空间分辨能力研究及其优化

超快电子衍射技术是研究物质瞬态结构变化及超快结构动力学的有效手段.研制了国内第一套同时具有超快时间分辨及超高空间分辨能力的超快电子衍射系统,并研究了在该超快电子衍射系统上实现超快时间分辨及超高空间分辨能力的技术手段及其优化方法.实验结果表明：经过优化后该系统可以具有优于500 fs的时间分辨能力,其空间分辨能力达到0.04%的衍射峰位置变化,对应的晶面变化为0.0005?.该系统可以为实时测量超快光脉冲激发的物质瞬态结构变化,特别是为研究晶体材料的超快动力学行为提供了强有力的实验工具. 关键词： 超快电子衍射 空间分辨 时间分辨     

How to realize an ultrafast electron diffraction experiment with a terahertz pump: A theoretical study

To integrate a terahertz pump into an ultrafast electron diffraction (UED) experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly. However, the deflection of the electron probe by the electromagnetic field of the terahertz pump alters the incident angle of the electron probe on the sample, impeding it from recording structural information afterwards. In this article, we studied this issue by a theoretical simulation of the terahertz-induced deflection effect on the electron probe, and came up with several possible schemes to reduce such effect. As a result, a terahertz-pump-electron-probe UED experiment with a temporal resolution comparable to the terahertz period is realized. We also found that MeV UED was more suitable for such terahertz pump experiment.     

中国物理类期刊比较研究

从《中文核心期刊要目总览》和《中国科技期刊引证报告》出发,分析国内物理类的主要期刊．对这些期刊在SCI、EI的收录情况、影响因子等方面进行了比较研究,为我国的物理研究和期刊发展提供参考．