Author: Okayasu, Y.
Paper Title Page
MOAL2 The First Demonstration of EOS 3D-BCD Monitor to Maximize 3D-Overlapping for HHG-Seeded FEL 1
  • H. Tomizawa, T. Ishikawa, K. Ogawa, H. Tanaka, M. Yabashi
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  • S. Matsubara, Y. Okayasu, T. Togashi
    JASRI/SPring-8, Hyogo, Japan
  In FEL seeding as a full-coherent light source, a high hit rate of successfully seeded FEL pulses is required. Precise measurements of the electron bunch charge distribution (BCD) and its arrival timing are crucial keys to maximize and keep 3D overlapping between the high-order harmonics (HH) laser pulse and electron bunch. We constructed a relative timing drift monitor based on EOS, which measured the timing differences between the seeding HH-laser pulse and the electron bunch, using a common external laser source of both HH-driving and EO-probing pulses. The feedback system of timing drift was realized with real-time data processing of EO-signal spectra. Our system realized stable seeded FEL operation with a hit rate of 30%. The 3D-BCD monitor enables non-destructive measurements of the longitudinal and transverse BCD at the same time. The transverse detection can be used to control the relative pointing between HH-pulse and electron bunch. We also verified this transverse detection with multiple EO crystals at the EUV-FEL accelerator. Our next target for temporal resolution is 30 fs, with an octave-band EO-probing for DAST crystals, aiming FEL seeding in the soft X-ray region.  
slides icon Slides MOAL2 [59.364 MB]  
WEPC35 Progress Report of the Spectral Decoding Based EOS with Organic Pockels EO Crystals 765
  • Y. Okayasu, S. Matsubara, H. Tomizawa
    JASRI/SPring-8, Hyogo, Japan
  • T. Matsukawa, H. Minamide
    RIKEN ASI, Sendai, Miyagi, Japan
  • K. Ogawa
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  Funding: Grant-in-Aid for Scientific Research (Japan Society for the Promotion of Science, Grants No. 20612024 and No. 23360045)
So far, the temporal structure of ultrashort electron bunches has been extensively investigated by various kinds of electro-optic sampling (EOS) techniques, such as temporal, spectral and spatial decoding method, at several FEL accelerator facilities since early 2000’s. Inorganic Pockels EO crystals, i.e., GaP and ZnTe, have been generally utilized for the EOS. On the other hand, since mid-1980’s, organic nonlinear optical materials have been extensively investigated and DAST*, which has fast temporal response in the EO effect, was developed in 1986**. DAST is transparent in visible near to IR wavelength range and absorbent in 0.8-1.3 THz. We introduced the DAST crystal into the EOS and successfully demonstrated the first observation of the bunch charge distribution at the EUV-FEL accelerator, SPring-8 on February 2012***. Through the previous experiment, it is found that the EO signal intensity was gradually decreased. On March and April 2013, we prepared DAST crystals with variety of thickness and succeeded to compare EO signal intensities with different bunch charges. Recent results of both optical and structural analysis will be reported in addition to experimental results.
*4-N, N-dimethylamino-4’-N’-methyl stilbazolium tosylate
**S. Okada et al., Japan Patent Application 61-192404 (1986)
***Y. Okayasu et al., Phys. Rev. ST Accel. Beams 16, 052801 (2013)