• R.K. Li, H. Chen, Q. Du, T. Du, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, X. H. Lu, J. Shi, C.-X. Tang, H. S. Xu, L.X. Yan
  TUB, Beijing

Recent years have witnessed rapid advances of MeV ultrafast electron diffraction (UED), in which high quality, ultrashort, MeV electron pulses from a photocathode RF gun are employed as probes for ultrafast structural dynamics. We've built a prototype MeV UED system at the Accelerator Laboratory of Tsinghua University, optimized the the electron pulse parameters as well as hardware performances, and achieved high quality single-shot diffraction patterns. Moreover, MeV UED can be operated in a so-called 'continuously time-resolved (CTR)' mode, in which an RF deflecting cavity streaks the electron pulse thus each diffraction pattern constitutes an 'atomic movie'. We report our experimental progress on MeV UED in this paper.

• L.X. Yan, Q. Du, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C. Liao, C.-X. Tang
  TUB, Beijing

Ultrashort relativistic electron beam can be applied to produce high power coherent THz radiation by mechanisms such as FEL, CSR, CTR et al. The THz modulated electron beams, or THz-repetition-rate ultrashort electron bunch trains exhibit further enhancement of coherent THz radiation. This article will report the experimental results on the ultrashort electron bunch train production by copper based photocathode RF gun via direct UV laser pulse stacking using birefringent α-BBO crystal serials at our laboratory. The temporal profile of the electron beam was measured by deflecting cavity. Space charge effect downstream the photocathode is simulated. This shaping method of laser pulse by α-BBO crystals can also be applied to form quasi flattop UV laser pulse for reducing the initial emittance of the electron beam from the photocathode RF gun.