title: Saturable absorption of intense hard X-rays in iron.
abstract: In 1913, Maurice de Broglie discovered the presence of X-ray absorption bands of silver and bromine in photographic emulsion. Over the following century, X-ray absorption spectroscopy was established as a standard basis for element analysis, and further applied to advanced investigation of the structures and electronic states of complex materials. Here we show the first observation of an X-ray-induced change of absorption spectra of the iron K-edge for 7.1-keV ultra-brilliant X-ray free-electron laser pulses with an extreme intensity of 10(20) W cm(-2). The highly excited state yields a shift of the absorption edge and an increase of transparency by a factor of 10 with an improvement of the phase front of the transmitted X-rays. This finding, the saturable absorption of hard X-rays, opens a promising path for future innovations of X-ray science by enabling novel attosecond active optics, such as lasing and dynamical spatiotemporal control of X-rays.
authors.affiliation: 1] Institute for Laser Science, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan [2] RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan.
authors.forename: Hitoki
authors.initials: H
authors.lastname: Yoneda
authors.affiliation: 1] RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan [2] Japan Synchrotron Radiation Research Institute (JASRI), Kouto 1-1-1, Sayo, Hyogo 679-5198, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Inubushi
authors.affiliation: RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan.
authors.forename: Makina
authors.initials: M
authors.lastname: Yabashi
authors.affiliation: 1] RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan [2] Japan Synchrotron Radiation Research Institute (JASRI), Kouto 1-1-1, Sayo, Hyogo 679-5198, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Katayama
authors.affiliation: RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: 1] RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan [2] Japan Synchrotron Radiation Research Institute (JASRI), Kouto 1-1-1, Sayo, Hyogo 679-5198, Japan.
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Ohashi
authors.affiliation: Japan Synchrotron Radiation Research Institute (JASRI), Kouto 1-1-1, Sayo, Hyogo 679-5198, Japan.
authors.forename: Hirokatsu
authors.initials: H
authors.lastname: Yumoto
authors.affiliation: 1] RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan [2] Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
authors.forename: Kazuto
authors.initials: K
authors.lastname: Yamauchi
authors.affiliation: 1] RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan [2] Department of Precision Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Mimura
authors.affiliation: Department of Physics, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Hikaru
authors.initials: H
authors.lastname: Kitamura