Abstract
X-ray free-electron lasers1,2 produce intense femtosecond pulses that have applications in exploring new frontiers in science. The unique characteristics of X-ray free-electron laser radiation can be enhanced significantly using focusing optics3. However, with such an optical device, even a slight deviation from the ideal design can lead to considerable errors in the focusing properties. Here, we present reflective optics comprising elliptically figured mirrors with nanometre accuracy to preserve a coherent wavefront, successfully focusing a 10 keV X-ray free-electron laser to the small area of 0.95 × 1.20 µm2. The near 100% efficiency of this arrangement allows an enormous 40,000-fold increase in the fluence to a power density of 6 × 1017 W cm−2. This achievement is directly applicable to the generation of a nanometre-size beam with an extreme power density of >1 × 1022 W cm−2, which will play a crucial role in the advance of microscopic research towards ultimate ångstrom resolution, as well as in the development of nonlinear optical sciences under extreme conditions.
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Acknowledgements
This research was partially supported by a Grant-in-Aid for Scientific Research (S) (23226004) from the Ministry of Education, Sports, Culture, Science and Technology, Japan (MEXT), CREST from the Japan Science and Technology Agency (JST), the X-ray Free Electron Laser Utilization Research Project of MEXT, and the Proposal Program of SACLA Experimental Instruments of RIKEN. The authors thank Hitachi High-Technologies Corporation for providing scanning electron microscope images for Fig. 3.
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H.Yu. and M.Y. wrote the first draft of the manuscript. The design of the focusing mirrors and the mirror manipulator, wave-optical analysis and the experiment using XFEL were carried out mainly by H.Yu., H.M., T.Ko., S.M., T.Ki., H.Yo. and J.K. The conditions for this experiment at SACLA were set up by K.T., T.To., Y.I. and T.S. The simulator of the electron-beam dynamics was developed by T.Ta. The mirror substrates were fabricated by Y.H. and H.Ohm. Experimental planning was carried out by Y.S., M.Y., H.Oha., T.I. and K.Y.
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Yumoto, H., Mimura, H., Koyama, T. et al. Focusing of X-ray free-electron laser pulses with reflective optics. Nature Photon 7, 43–47 (2013). https://doi.org/10.1038/nphoton.2012.306
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DOI: https://doi.org/10.1038/nphoton.2012.306
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