Ultrafast electron diffraction using photocathode microwave electron guns is a powerful tool for investigating ultrafast science. To improve the spatial and temporal resolution of diffraction, it is crucial to enhance the quality of the electron beam, particularly the initial quality of the electron beam emitted from the photocathode that is influenced by the driving laser. To meet the strict requirements, the performance parameters of the femtosecond laser transmission system play a significant role. In this paper, we analyze the impact of femtosecond laser system parameters on diffraction resolution and investigate the primary indicators of the femtosecond laser system. We conducted experiments to measure the primary parameters of the laser, including pointing stability, beam diameter, pulse width, and pulse energy. Based on the experimental results and considering the complexity of engineering implementation, we proposed an optical scheme for the femtosecond laser transmission path to satisfy the requirements of the ultrafast electron diffraction device for further improving the diffraction resolution. This research aims to provide valuable insights into optimizing the femtosecond laser system for ultrafast electron diffraction experiments.
Mega-electron-Volt Ultrafast Electron Microscope (MeV UEM) has become a promising tool to real-time observe ultrafast dynamics at the atomic scale, where a magnetic objective lens system is critical to manipulating the high-energy beam to achieve point-to-point imaging. However, the upper limit of spatial resolution is mainly determined by the high-order chromatic aberration resulting from the electron energy spread and the imaging lens system. A magnetic lens system based on the Russian Quadruplet (RQ) is being studied to improve the degree of symmetry and further reduce the aberration. The beam optics design and multi-target optimization are finished to achieve a good spatial resolution of point-to-point imaging. This paper will introduce the theoretical deviation and design results of our first-stage imaging lens system, and second-order beam optics is optimized further to improve the resolution.
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