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- H. Tomizawa, T. Hara, T. Ishikawa, K. Ogawa, H. Tanaka, T. Tanaka, T. Togashi, K. Togawa, M. Yabashi
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
- M. Aoyama, K. Yamakawa
JAEA/Kansai, Kyoto, Japan
- A. Iwasaki, S. Owada, T. Sato, K. Yamanouchi
The University of Tokyo, Tokyo, Japan
- S. Matsubara, Y. Okayasu, T. Watanabe
JASRI/SPring-8, Hyogo-ken, Japan
- K. Midorikawa, E. Takahashi
RIKEN, Saitama, Japan
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We performed the higher-order harmonic (HH) seeded FEL operation at a 61.2 nm fundamental wavelength, using a seeding source of HH pulses from a Ti:sapphire laser at the SCSS (EUV-FEL) accelerator. It is important for the HH seeded FEL scheme to synchronize the seeding laser pulses to the electron bunches. We constructed the relative arrival timing monitor based on Electro-Optic sampling (EOS). Since the EOS-probe laser pulses were optically split from HH-driving laser pulses, the arrival time difference of the seeding laser pulses, with respect to the electron bunches, were measured bunch-by-bunch. This non-invasive EOS monitor made uninterrupted, real-time monitoring possible even during the seeded FEL operation. The EOS system was used for the arrival timing feedback with a few-hundred-femtosecond adjustability for continual operation of the HH-seeded FEL. By using the EOS-locking system, the HH seeded FEL was operated over half a day with a 20-30% hit rate. The output pulse energy reached 20uJ at the 61.2 nm wavelength. A user experiment was performed by using the seeded EUV-EL and a clear difference between the SASE-FEL and the seeded FEL was observed.
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