Few-Femtosecond MeV Electron Bunches for Ultrafast Electron Diffraction

Herein, we propose a technique for megaelectronvolt ultrafast electron diffraction that can achieve a few-femtosecond time resolution. The technique modulates a relativistic electron beam using two radially polarized laser pulses of varying frequencies, which enable the condensation of the electrons into an ultrashort pulse. Moreover, our study shows that this technique can suppress the arrival-time jitter of the electron beam at the sample location. Numerical simulations show that using realistic laser parameters corresponding to the current gigawatt-power-level laser systems, a 3.3-fs (rms over 45% charge) electron beam can be obtained and the arrival-time jitter can be 1.35 fs (rms). This technique may have a considerable impact on ultrafast electron diffraction, microscopy, and other ultrafast research facilities that require few-femtosecond electron beams with a small time jitter.