中文摘要：

根据已有文献研究结果，建立了Boersch效应电子脉冲展宽物理分析模型，确立了以时间弥散特征参量为核心参数的电子脉冲展宽表征理论，以此为基础分析了超短电子脉冲展宽对外场的依赖性。结果表明：相比匀速漂移场，加速场具有较好的抑制电子脉冲展宽作用，而减速场则增大了电子脉冲展宽；对条纹相机和超快电子衍射仪等电子枪系统而言，除了已知的两个区域-光阴极附近和偏转板后等电位漂移空间之外，光电子脉冲从高电位向低电位传输时其时间弥散也是非常显著的。此结论对高性能电子枪工程设计具有重要的理论指导价值。

英文摘要：

Boersch effect of electron pulse broadening was modeled and analyzed, based on the existing results re- ported in literature. A theory to characterize the electron packet broadening was formulated, with the time dispersion char- acteristics as the major factor. The influence of the external electric field on the ultra-short electron packet broadening was evaluated, in the newly-developed theory. The results show that the external e-field, accelerating the electrons, suppresses the broadening;whereas the field, decelerating electrons, widens the broadening. In image-converter streak cameras and uhm-fast electron diffraction devices, there exist one non-equipatential and two known equi-potential regions：one situates in the vicinity of photocathode, the other lies behind the deflection plate. Our preliminary results are of much technological interest for design of high-performance electron gun, because significant time broadening originates from the transit of the photoelectron packet in the potential decreasing direction.