Femtosecond mega-electron-volt electron microdiffraction

Abstract

Instruments to visualize transient structural changes of inhomogeneous materials on the nanometer scale with atomic spatial and temporal resolution are demanded to advance materials science, bioscience, and fusion sciences. One such technique is femtosecond electron microdiffraction, in which a short pulse of electrons with femtosecondscale duration is focused into a micron-scale spot and used to obtain diffraction images to resolve ultrafast structural dynamics over localized crystalline domain. In this letter, we report the experimental demonstration of time-resolved mega-electron-volt electron microdiffraction which achieves a 5 μm root-mean-square (rms) beam size on the sample and a 100 fs rms temporal resolution. Using pulses of 10k electrons at 4.2 MeV energy with a normalized emittance 3 nm-rad, we obtained high quality diffraction from a single 10 μm paraffin ( ) crystal. The phonon softening mode in optical-pumped polycrystalline Bi was also time-resolved, demonstrating the temporal resolution limits of our instrument design. This new characterization capability will open many research opportunities in material and biological sciences.Time-resolved x-ray 1-3 and electron microbeams 4-6 are emerging tools with broad applications in science and technology. Achieving high temporal resolving power provides insight into structural dynamics of materials in non-equilibrium states for understanding and controlling of energy and matter 7 . Delivering a focused, micron-scale beam to a sample under study is of paramount importance, as it enables the study of samples that cannot be prepared at the macroscale, or are intrinsically inhomogeneous. For example, the lateral size of a "large" protein crystal is typically less than 100 μm. Further, small protein crystals almost always exhibit greater perfection and less impurity than large crystals 8 . Matching the beam size to that of the small protein crystal sample provides the best signal-to-noise (SNR) ratio for crystallography. The inhomogeneous nature of natural and nanoscale materials also requires micron-scale probes to determine local composition, chemistry, and crystalline structure. With the advent of high brightness x-ray free-electron lasers and efficient x-ray focusing optics, x-ray microbeams with femtosecond level temporal resolving power have been achieved [9][10][11][12] . Extensive research and development efforts are underway to push the frontier of electron microbeams towards the femtosecond time scales temporal resolution in the Ultrafast Electron Diffraction (UED).Electron microdiffraction with continuous wave beams is a well-established technique in conventional transmission electron microscopy (TEM) 13 . Recently, ultrafast electron microscopy has been built by modifying a conventional TEM from thermionic or field emission electron sources to ultrafast laser-excited photoemission electron sources [14][15] , allowing timeresolved optical pump -electron probe experiments. Dedicated kilo-electron-volt (keV) ultrafast electron diffraction machines ha...

Light-induced charge density wave in LaTe3

“…MeV ultrafast electron diffraction. The experiments were carried out in the Accelerator Structure Test Area facility at SLAC National Laboratory [29,30]. The 800-nm (1.55-eV), 80-fs pump pulse from a commercial Ti:sapphire regenerative amplifier (RA) laser (Vitara and Legend Elite HE, Coherent Inc.) were focused to an area larger than 500 × 500 µm 2 (FWHM) in the sample at an incidence angle around 5 • from sample normal.…”

Ultrafast manipulation of mirror domain walls in a charge density wave

“…The experiments on mirror DW manipulation and CDW amplitude mode characterization ( Fig. 2-4, S4, and S5) were carried out in the MeV UED setup in the Accelerator Structure Test Area facility at SLAC National Laboratory (35). Fig.…”

A Compact Ultrafast Electron Diffractometer with Relativistic Femtosecond Electron Pulses

“…In recent years, relativistic-energy UEDs were developed with an advanced particle accelerator technology of photocathode radio-frequency electron gun (rf gun) [8][9][10][11][12][13][14][15]. Recently, an ultrafast electron microscope (UEM) using the rf gun has been developed at Osaka University [16,17].…”

“…However, in the current relativistic UED instruments, a relatively long distance of 4 m or more between the sample and detector is required to record the acceptable diffraction images [13][14][15]. Many significant efforts, including the generation of high-quality electron pulses and the construction of compact UED with high tempo-spatial resolution and good signal-to-noise ratio, are required for this approach to be realized.…”