The hard X-ray free-electron laser at the Pohang Accelerator Laboratory (PAL-XFEL) in the Republic of Korea achieved saturation of a 0.144 nm free-electron laser beam on 27 November 2016, making it the third hard X-ray free-electron laser in the world, following the demonstrations of the Linac Coherent Light Source (LCLS) and the SPring-8 Angstrom Compact Free Electron Laser (SACLA). The use of electron-beam-based alignment incorporating undulator radiation spectrum analysis has allowed reliable operation of PAL-XFEL with unprecedented temporal stability and dispersion-free orbits. In particular, a timing jitter of just 20 fs for the free-electron laser photon beam is consistently achieved due to the use of a state-of-the-art design of the electron linear accelerator and electron-beam-based alignment. The low timing jitter of the electron beam makes it possible to observe Bi(111) phonon dynamics without the need for timing-jitter correction, indicating that PAL-XFEL will be an extremely useful tool for hard X-ray time-resolved experiments.
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The authors thank K.J. Kim, P. Emma, Z. Huang, P. Krejcik, A. Young, S. Hoobler, C. Xu, T. Straumann, K. Kim, Y. Ding, F. Zhou, D. Ratner, T. Raubenheimer, J. Wu, J. Pflueger and H. Matsumoto for their help. The authors also thank S.L. Cho for providing Bi thin-film samples and H. Loos and J. Loos for their contribution to the PAL-XFEL commissioning. The authors acknowledge the support of the Ministry of Science and ICT of Korea.
The authors declare no competing financial interests.
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