Crucial for the field of ultrafast electron microscopy is the creation of sub-picosecond, high brightness electron pulses. The use of a blanker to chop the beam that originates from a high brightness Schottky source may provide an attractive alternative to direct pulsed laser illumination of the source. We have recently presented the concept of a laser-triggered ultrafast beam blanker and argued that generation of 100 fs pulses could be possible [Weppelman et al., Ultramicroscopy 184, 8-17 (2017)]. However, a detailed analysis of the influence of a deflection field changing sign on sub-picoseconds time scale on the quality of the resulting electron pulses has so far been lacking. Here, we present such an analysis using time-dependent, three-dimensional numerical simulations to evaluate the time-evolution of deflection fields in and around a micrometers-scale deflector connected to a photo-conductive switch. Further particle tracing through the time-dependent fields allows us to evaluate beam quality parameters such as energy spread and temporal broadening. We show that with a shielded, "tunnel-type" design of the beam blanker limiting the spatial extent of fringe fields outside the blanker, the blanker-induced energy spread can be limited to 0.5 eV. Moreover, our results confirm that it could be possible to bring laser-triggered 100 fs focused electron pulses on the sample using a miniaturized ultrafast beam blanker. This would enable us to resolve ultrafast dynamics using focused electron pulses in an SEM or STEM.

中文翻译：

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超快束消隐器产生的电子脉冲的脉冲长度，能量扩散和时间演变。

超快电子显微镜领域的关键是亚皮秒级高亮度电子脉冲的产生。使用消隐器斩波来自高亮度肖特基光源的光束可以为光源的直接脉冲激光照明提供有吸引力的替代方法。我们最近提出了激光触发的超快光束消隐器的概念，并认为可能会产生100 fs的脉冲[Weppelman等人，Ultramicroscopy 184，8-17（2017）]。但是，迄今为止，还缺乏对偏转场变化符号对亚皮秒级时标对所得电子脉冲质量的影响的详细分析。在这里，我们使用时间相关的方法进行这种分析，三维数值模拟，以评估与光电导开关相连的微米级偏转器及其周围偏转场的时间演化。通过与时间有关的场进行进一步的粒子追踪，使我们能够评估光束质量参数，例如能量扩散和时间展宽。我们显示出，用光束消隐器的屏蔽“隧道型”设计限制消隐器外部边缘场的空间范围，消隐器引起的能量散布可以限制为0.5 eV。此外，我们的结果证实，使用小型超快束消隐器可以将激光触发的100 fs聚焦电子脉冲带到样品上。这将使我们能够使用SEM或STEM中的聚焦电子脉冲来解决超快速动力学问题。