D. McCormick

Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory

Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 μm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime.