Ultrafast Electron Diffraction with MeV Electron Beams

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Ultrafast diffraction is a powerful tool for studying lattice vibrations, phase transitions, chemical reactions, and strongly-correlated electron materials. Ultrafast electron diffraction (UED) has the advantage over other probes of a large interaction cross-section and compact facilities. However, due to space charge effects and velocity mismatch between pump and probe, the time resolution of conventional UED is limited to the pico-second to few pico-second range. On the other hand, UED with relativistic electron beams of MeV energy has the potential to exceed these limits. At BNL we have succeeded in the first experimental demonstration of electron diffraction with 100 fs time resolution, using MeV electron beams. We obtain high quality, single-shot electron diffraction for both poly-crystal aluminium and single-crystal 1T-TaS2 using a 5 femto-Coulomb (105 electrons) electron beam. The timing jitter is measured to be 250 fs. The time resolution is shown to be 100 fs (rms) by studying the evolution of Bragg and super-lattice peaks of 1T-TaS2 following an optical pump. Our results also demonstrate the feasibility of ultimately realizing 10 femto-second time resolved electron diffraction.

This work was supported by the U.S. Department of Energy Office of Science.

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