Author: Kim, M.H.
Paper Title Page
Ultrafast Electron Diffraction Facility Based on an RF Photogun and Achromatic 90-degree Bends for Sub-100-Femtosecond Timing Jitter  
  • Y.U. Jeong, S. Bae, I.H. Baek, B.A. Gudkov, B. Han, K.H. Jang, H.W. Kim, M.H. Kim, Y.-C. Kim, K. Lee, S.V. Miginsky, J. Mun, J.H. Nam, S. Park, S. Setiniyaz
    KAERI, Daejon, Republic of Korea
  • R. Fabian, H. Ihee, J. Kim, K.Y. Oang, H. Yang
    KAIST, Daejeon, Republic of Korea
  • J.H. Han
    PAL, Pohang, Kyungbuk, Republic of Korea
  • H.W. Kim
    University of Science and Technology of Korea (UST), Daejeon, Republic of Korea
  • K.W. Kim
    Chung Buk National University, Cheongju, Republic of Korea
  • S.V. Miginsky, N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  • S. H. Park
    Korea University Sejong Campus, Sejong, Republic of Korea
  • S. Park
    Kyungpook National University, Daegu, Republic of Korea
  We have developed a laboratory-scale ultrashort electron accelerator for investigating femtosecond dynamics of atoms or molecules with pump-probe experiments. This system includes an S-band radio-frequency (RF) photogun and four achromatic bends for compressing electron bunches. Two of them are for ultrafast electron diffraction (UED) experiments on solid and gas samples. The electron bunch duration at the UED beamlines was designed to be ~30 fs in rms. Our target value of the timing jitter between the pumping laser pulse and probing electron bunch is approximately 10 fs. The synchronization between the pumping laser oscillator and a master oscillator of the RF system was successfully performed with the extremely low timing fluctuation of ~10 fs during 24-hour operation*. We developed a high-intense terahertz pumping source with field strength of more than 0.5 MV/cm for THz-pump and electron-probe experiments. We are conducting three independent application experiments with superconducting and strongly-correlated materials and gas samples for ultrafast molecular dynamics.
* H. Yang et al., "10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources," Scientific Reports, 7, 39966, 2017.
Development of T-Ray-Pumped Ultrafast Electron Diffraction Beamline  
  • I.H. Baek, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, M.H. Kim, Y.-C. Kim, K. Lee, J.H. Nam, S. Park
    KAERI, Daejon, Republic of Korea
  • N.A. Vinokurov
    NSU, Novosibirsk, Russia
  Ultrashort electron diffraction (UED) technique has triggered numerous fundamental studies and technological applications. For a resonant control of materials, the intense T-ray has been regarded as a crucial tool because its low photon energy can excite an extremely low energy level of atomic or molecular system selectively. In this work, we present the ultrafast T-ray-pump/electron-probe crystallography system for observing the structural dynamics of temperature-controlled materials. T-ray with energies of few microjoule is generated from the nonlinear optical crystal lithium niobate and utilized as a pumping source. Three-MeV electron bunches are produced by the RF-photogun with 2.856 GHz and utilized as a diffraction tool. The isochronous bending structure compresses an electron bunch length to ~30 femtoseconds. We believe that our system can guide the way to understand fundamental phenomena in nature.