| Paper |
Title |
Page |
| MOPPH054 |
Spectral Characteristics of the Seeded FEL Using Higher Harmonic Generation in a Gas at the SCSS Test Accelerator
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106 |
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- T. Tanikawa
Sokendai, Okazaki, Aichi
- B. Carré, D. Garzella, M. Labat
CEA, Gif-sur-Yvette
- M.-E. Couprie
SOLEIL, Gif-sur-Yvette
- T. Hara, T. Ishikawa, H. Kitamura, T. Shintake, T. Tanaka, M. Yabashi
RIKEN/SPring-8, Hyogo
- M. Katoh
UVSOR, Okazaki
- G. Lambert
LOA, Palaiseau
- K. Tahara, Y. T. Tanaka
RIKEN Spring-8 Harima, Hyogo
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Seeding a FEL with high order harmonic generation (HHG) from a Xe gas cell at the SCSS test accelerator was achieved at a wavelength of 160 nm (the 5th harmonic of a Ti: Sa laser) in December 2006. After the improvement of the accelerator performance in 2007, we performed detailed studies of the spectral characteristics of the seeded FEL. Compared to the spiky spectrum of SASE, the seeded FEL can produce a quasi-Gaussian spectrum with a single peak. In addition, the lasing wavelength is fixed at the wavelength of the seed, even if the undulator K-parameter is shifted in a certain range. Therefore, the spectral stability becomes much better than SASE against the fluctuation of undulator fields or beam energy. In the recent experiments, we observed that the bandwidth of the amplified seed became narrower than that of the original seed light itself. It seems to be stretched the longitudinal coherent length in the FEL interaction. In the presentation, we will report the spectral characteristics of the seeded FEL.
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| MOPPH072 |
Operation of the UVSOR-II FEL in Helical Mode
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143 |
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- M. Labat
CEA, Gif-sur-Yvette
- M.-E. Couprie
SOLEIL, Gif-sur-Yvette
- M. Hosaka
Nagoya University, Nagoya
- M. Katoh, M. Shimada
UVSOR, Okazaki
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Seeded Free Electron Lasers (FELs) - an external laser source is injected inside the undulator to perform energy modulation of the electron beam - deliver intense, short duration, short wavelength light pulses with a high temporal coherence degree. Since the polarization of the radiation depends on the undulator magnetic field, the FELs operated with adjustable undulators are unique candidates for providing flexible polarized light of high quality, required for probing symmetry properties of matter. Experiments have been performed on the UVSOR-II storage ring FEL in the seeded Coherent Harmonic Generation (CHG) scheme operated with helical undulators. The electron beam stored at 500 MeV is seeded using a 800 nm Ti:Sa laser, allowing radiation at 400 nm (second harmonic). A quarter-wavelength plate allows the tuning of the polarization of the seeded laser from linear to elliptic or circular. We show that the FEL radiation intensity can be significantly improved via the seed polarization matching. Other parameters of optimization are also presented, such as the focussing mode. The experimental results are analysed using a simple 1D analytical model and the 3D numerical code GENESIS.
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