Abstract
Terahertz pulses accelerating and scanning electron beam can break through the limitation of accelerating electric field between cathodes and grids in traditional streak tubes, thus reducing the time dispersion and enhancing the temporal resolution of time-scanning detectors. Based on this new technology, in this paper an ultra-small structured time-resolved detector with no focusing pole is designed. The terahertz pulse coupling/enhancing device suitable for acceleration zone and scanning zone is designed and optimized. The enhanced coefficient of the terahertz pulse electric field in the device reaches 9.39. In the paper, the relationship between time dispersion in acceleration zone and the moment of electrons emission is analyzed theoretically. We also analyze the influence of space charge effect on time dispersion. The electronic trajectory tracking is used to calculate and analyze the time dispersion of this detector, and finally the time resolution is better than 50fs.
Highlights
scanning electron beam can break through the limitation of accelerating electric field
We also analyze the influence of space charge effect on time dispersion
finally the time resolution is better than 50fs
Summary
电子的加速; 在扫描腔内, 电场垂直于电子入射 方向, 实现对电子的偏转. 探测器整体结构示意 图如图 2 所示, 图 2(a) 和图 2(b) 分别是探测器加 速及扫描结构的三维图和俯视图. 另外, 输入的 太赫兹脉冲波形和在加速腔和扫描腔中心的波形 如图 3 所示. 探测器整体结构示意 图如图 2 所示, 图 2(a) 和图 2(b) 分别是探测器加 速及扫描结构的三维图和俯视图. 仿 真 采 用 的太赫兹脉冲波形在前者基础上进行降噪和平滑, 如图 4(b) 所示. A 点 (0 ps) 为电场正半个脉冲的 起始时刻, B 点 (0.588 ps) 为正半脉冲峰值, 幅度 350 MV/m, 正半个脉冲的全宽 AC 为 1.311 ps, E 点之后电场强度为 0. 为了让分析清晰明了, 这里 做出一些合理的限定 : 1) 电子发射时刻在A—B 段内, 在 B 点后发射的电子的加速时间短, 导致飞行时间增大并产生严重的时间弥散; 2) 本 节仅考虑太赫兹加速电场对时间弥散的贡献, 在 第 4 节讨论空间电荷效应影响; 3) 用电子脉冲的 首尾两个电子间的时间展宽代表电子脉冲整体的. 图 4 (a) 实际太赫兹脉冲电场波形及频谱; (b) 计算时采用的太赫兹脉冲电场强度波形 Fig. 4. (a) Actual wave form of THz pulse’ s electric field and spectrum; (b) wave form of THz pulse’ s electric field in the calculation 图 4 (a) 实际太赫兹脉冲电场波形及频谱; (b) 计算时采用的太赫兹脉冲电场强度波形 Fig. 4. (a) Actual wave form of THz pulse’ s electric field and spectrum; (b) wave form of THz pulse’ s electric field in the calculation
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