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A compact free-electron laser for generating coherent radiation in the extreme ultraviolet region


Single-pass free-electron lasers based on self-amplified spontaneous emission1,2,3,4 are enabling the generation of laser light at ever shorter wavelengths, including extreme ultraviolet5, soft X-rays and even hard X-rays6,7,8. A typical X-ray free-electron laser is a few kilometres in length and requires an electron-beam energy higher than 10 GeV (refs 6, 8). If such light sources are to become accessible to more researchers, a significant reduction in scale is desirable Here, we report observations of brilliant extreme-ultraviolet radiation from a 55-m-long compact self-amplified spontaneous-emission source, which combines short-period undulators with a high-quality electron source operating at a low acceleration energy of 250 MeV. The radiation power reaches saturation at wavelengths ranging from 51 to 61 nm with a maximum pulse energy of 30 µJ. The ultralow emittance (0.6π mm mrad) of the electron beam from a CeB6 thermionic cathode9 is barely degraded by a multiple-stage bunch compression system that dramatically enhances the beam current from 1 to 300 A. This achievement expands the potential for generating X-ray free-electron laser radiation with a compact 2-GeV machine.

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Figure 1: Profile of the electron beam.
Figure 2: Schematic configuration of the SCSS test accelerator.
Figure 3: Pulse energy and fluctuation of the SASE radiation.
Figure 4: Spectra for SASE radiation.


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The authors express special thanks to the staff of SPring–8, in particular to T. Hasegawa and S. Tanaka for machine operation, S. Kojima, S. Indo and K. Nakashima for their technical support, H. Tomizawa for his outstanding insights, and H. Suematsu, N. Kumagai and H. Ohno for their continuous encouragement. We also thank H. Matsumoto and H. Baba for developing the C-band accelerator system.

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Correspondence to Makina Yabashi, Yujong Kim, Masanobu Kitamura, Kazuyuki Onoe or Tetsuya Takagi.

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Shintake, T., Tanaka, H., Hara, T. et al. A compact free-electron laser for generating coherent radiation in the extreme ultraviolet region. Nature Photon 2, 555–559 (2008).

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