1. Breaking 50 Femtosecond Resolution Barrier in MeV Ultrafast Electron Diffraction with a Double Bend Achromat Compressor
- Author
-
Chao Lu, Zhuoran Ma, Dao Xiang, Weishi Wan, Fengfeng Qi, Tao Jiang, Wenxiang Jiang, Lingrong Zhao, Dong Qian, Jie Zhang, Pengfei Zhu, Xiao Zou, Yun Cheng, Wentao Zhang, and Zhe Wang
- Subjects
Physics ,business.industry ,Ultrafast electron diffraction ,General Physics and Astronomy ,Electron ,01 natural sciences ,Time of flight ,Optics ,Electron diffraction ,Temporal resolution ,0103 physical sciences ,Femtosecond ,Chirp ,Cathode ray ,Physics::Accelerator Physics ,010306 general physics ,business - Abstract
We propose and demonstrate a novel scheme to produce ultrashort and ultrastable MeV electron beam. In this scheme, the electron beam produced in a photocathode radio frequency (rf) gun first expands under its own Coulomb force with which a positive energy chirp is imprinted in the beam longitudinal phase space. The beam is then sent through a double bend achromat with positive longitudinal dispersion where electrons at the bunch tail with lower energies follow shorter paths and thus catch up with the bunch head, leading to longitudinal bunch compression. We show that with optimized parameter sets, the whole beam path from the electron source to the compression point can be made isochronous such that the time of flight for the electron beam is immune to the fluctuations of rf amplitude. With a laser-driven THz deflector, the bunch length and arrival time jitter for a 20 fC beam after bunch compression are measured to be about 29 fs (FWHM) and 22 fs (FWHM), respectively. Such an ultrashort and ultrastable electron beam allows us to achieve 50 femtosecond (FWHM) resolution in MeV ultrafast electron diffraction where lattice oscillation at 2.6 THz corresponding to Bismuth A_{1g} mode is clearly observed without correcting both the short-term timing jitter and long-term timing drift. Furthermore, oscillating weak diffuse scattering signal related to phonon coupling and decay is also clearly resolved thanks to the improved temporal resolution and increased electron flux. We expect that this technique will have a strong impact in emerging ultrashort electron beam based facilities and applications.
- Published
- 2020