| 超紧凑型飞秒电子衍射仪的设计 |
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| 引用本文： | 罗端,惠丹丹,温文龙,李立立,辛丽伟,钟梓源,吉超,陈萍,何凯,王兴,田进寿. 超紧凑型飞秒电子衍射仪的设计[J]. 物理学报, 2020, 0(5): 26-37 |
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| 作者姓名： | 罗端 惠丹丹 温文龙 李立立 辛丽伟 钟梓源 吉超 陈萍 何凯 王兴 田进寿 |
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| 作者单位： | 中国科学院西安光学精密机械研究所;中国科学院大学;山西大学 |
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| 基金项目： | 国家自然科学基金青年科学基金(批准号:11805267,71705255)资助的课题~~ |
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| 摘 要： | 由于空间电荷效应的限制,产生百飞秒的极短电子脉冲是超快电子衍射技术的一大难点.同时,电子的穿透深度随着电子能量的增加而增加,而电子的散射几率却具有相反的规律.因而,除了时间分辨的提升,还需要可宽范围调节的电子能量以优化不同厚度样品对其的需求.基于此,提出并设计了一种新型超紧凑电子枪,结合均匀场阴极和可移动阳极的配置,可在10-125 kV加速电压范围内实现100 fs量级时间分辨率.通过优化设计高压电极轮廓,使得其轴上和整个阴极面的场增强因子在不同阴阳极间距下均小于约4%,从而保证了不同加速电压下最大轴上场强均可达10 MV/m量级,有效地抑制了电子脉冲的展宽效应;进一步将阳极小孔设计成可放置致密电镜载网的阶梯孔,一方面可将载网支撑的样品紧贴小孔后方放置,最大程度上缩短了电子从阴极到样品的时间弥散,同时也可以有效地减弱阳极孔对电子束的散焦效应,提升电子束的横向聚焦性能.
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| 关 键 词： | 超快过程 分子电影 均匀场电极 超短电子源 |
Design of a femtosecond electron diffractometer with adjustable gaps |
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| Luo Duan,Hui Dan-Dan,Wen Wen-Long,Li Li-Li,Xin Li-Wei,Zhong Zi-Yuan,Ji Chao,Chen Ping,He Kai,Wang Xing,Tian Jin-Shou. Design of a femtosecond electron diffractometer with adjustable gaps[J]. Acta Physica Sinica, 2020, 0(5): 26-37 |
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| Authors: | Luo Duan Hui Dan-Dan Wen Wen-Long Li Li-Li Xin Li-Wei Zhong Zi-Yuan Ji Chao Chen Ping He Kai Wang Xing Tian Jin-Shou |
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| Affiliation: | (Key Laboratory of Ultra-fast Photoelectric Diagnostics Technology,Xi’an Institute of Optics and Precision Mechanics,Chinese Academy of Sciences,Xi'an 710119,China;University of Chinese Academy of Sciences,Beijing 100049,China;Collaborative Innovation Center of Extreme Optics,Shanxi University,Taiyuan 030006,China) |
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| Abstract: | One of the grand challenges in ultrafast science is real-time visualization of the microscopic structural evolution on atomic time and length scales. A promising pump-probe technique using a femtosecond laser pulse to initiate the ultrafast dynamics and another ultrashort electron pulse to probe the resulting changes has been developed and widely used to study ultrafast structural dynamics in chemical reactions, phase transitions,charge density waves, and even biological functions. In the past three decades, a number of different ultrafast electron guns have been developed to generate ultashort electron sources, mainly including hybrid electron gun with radio-frequency(RF) cavities for compressing the pulse broadening, relativistic electron gun for suppressing the coulomb interaction, single-electron pulses without space charge effect and compact direct current(DC) electron gun for minimizing the electron propagation distance. At present, these developments with different final electron energy and available total charge have improved the time response of ultrafast electron diffraction(UED) setups to a new frontier approaching to 100 fs regime. Although enormous efforts have been made, the superior capabilities and potentials of ultrafast electron diffraction(UED) are still hindered by space-charge induced pulse broadening. Besides, the penetration depth of electrons increases with the electron energy, while the scattering probability of electrons has the opposite consequence. Thus, in addition to the temporal resolution enhancement, it is also important that the electron energy should be tunable in a wide range to meet the requirements for samples with different thickness. Here in this work, we design a novel ultra-compact electron gun which combines a well-designed cathode profile, thereby providing a uniform field and a movable anode configuration to achieve a temporal resolution on the order of 100 fs over an accelerating voltage range from 10 kV to 125 kV. By optimizing the design of the high-voltage electrode profile, the field enhancement factor on the axis and along the cathode surface are both less than ~4% at different cathode-anode spacings, and thus the maximum on-axis field strength of ~10 MV/m is achieved under various accelerating voltages. This effectively suppresses the space charge broadening effect of the electron pulse. Furthermore, the anode aperture is designed as a stepped hole in which the dense sample grid can be placed, and the sample under study is directly supported by the grid and located at the anode, which reduces the cathode-to-sample distance, thus minimizing the electron pulse broadening from the cathode to sample. Moreover, the defocusing effect caused by the anode hole on the electron beam can be effectively reduced, therefore improving the lateral focusing performance of the electron beam. |
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| Keywords: | ultrafast process molecular movie uniform field electrode ultrashort electron sources |
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