Author
Tetsuya Ishikawa
Bio: Tetsuya Ishikawa is an academic researcher from Saitama Prefecture. The author has contributed to research in topics: Laser & Free-electron laser. The author has an hindex of 59, co-authored 545 publications receiving 15226 citations.
Topics: Laser, Free-electron laser, Diffraction, Synchrotron radiation, Beamline
Papers published on a yearly basis
Papers
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TL;DR: In this paper, the SPring-8 Angstrom Compact Free-Electron Laser (CFEL) was used for sub-angstrom fundamental-wavelength lasing at the Tokyo National Museum.
Abstract: Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.
1,467 citations
TL;DR: The revolutionary advances that are transforming x-ray sources and imaging in the 21st century are reviewed.
Abstract: X-ray crystallography has been central to the development of many fields of science over the past century. It has now matured to a point that as long as good-quality crystals are available, their atomic structure can be routinely determined in three dimensions. However, many samples in physics, chemistry, materials science, nanoscience, geology, and biology are noncrystalline, and thus their three-dimensional structures are not accessible by traditional x-ray crystallography. Overcoming this hurdle has required the development of new coherent imaging methods to harness new coherent x-ray light sources. Here we review the revolutionary advances that are transforming x-ray sources and imaging in the 21st century.
606 citations
TL;DR: In this paper, an in situ technique that corrects for wavefront aberrations and allows X-rays to be focused to a spot just 7 nm wide could provide a solution.
Abstract: X-ray sources such as free-electron lasers offer the potential to study matter at unprecedented spatial and temporal resolution. But that potential is limited by the poor quality of conventional X-ray optical elements. An in situ technique that corrects for wavefront aberrations and allows X-rays to be focused to a spot just 7 nm wide could provide a solution.
493 citations
TL;DR: The structural changes in PSII induced by two-flash illumination at room temperature at a resolution of 2.35 Å are described, providing a mechanism for the O=O bond formation consistent with that proposed previously.
Abstract: Photosystem II (PSII) is a huge membrane-protein complex consisting of 20 different subunits with a total molecular mass of 350 kDa for a monomer. It catalyses light-driven water oxidation at its catalytic centre, the oxygen-evolving complex (OEC). The structure of PSII has been analysed at 1.9 A resolution by synchrotron radiation X-rays, which revealed that the OEC is a Mn4CaO5 cluster organized in an asymmetric, 'distorted-chair' form. This structure was further analysed with femtosecond X-ray free electron lasers (XFEL), providing the 'radiation damage-free' structure. The mechanism of O=O bond formation, however, remains obscure owing to the lack of intermediate-state structures. Here we describe the structural changes in PSII induced by two-flash illumination at room temperature at a resolution of 2.35 A using time-resolved serial femtosecond crystallography with an XFEL provided by the SPring-8 angstrom compact free-electron laser. An isomorphous difference Fourier map between the two-flash and dark-adapted states revealed two areas of apparent changes: around the QB/non-haem iron and the Mn4CaO5 cluster. The changes around the QB/non-haem iron region reflected the electron and proton transfers induced by the two-flash illumination. In the region around the OEC, a water molecule located 3.5 A from the Mn4CaO5 cluster disappeared from the map upon two-flash illumination. This reduced the distance between another water molecule and the oxygen atom O4, suggesting that proton transfer also occurred. Importantly, the two-flash-minus-dark isomorphous difference Fourier map showed an apparent positive peak around O5, a unique μ4-oxo-bridge located in the quasi-centre of Mn1 and Mn4 (refs 4,5). This suggests the insertion of a new oxygen atom (O6) close to O5, providing an O=O distance of 1.5 A between these two oxygen atoms. This provides a mechanism for the O=O bond formation consistent with that proposed previously
455 citations
TL;DR: In this paper, a 55m-long compact self-amplified spontaneous emission (SEM) source with a low acceleration energy of 250 MeV was used to generate X-ray free-electron laser radiation with a 2-GeV machine.
Abstract: 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. Free-electron lasers can produce powerful pulses of radiation at very short wavelengths, even in the hard-X-ray region. In general, however, they comprise facilities several kilometres in length. A 55-m-long laser could open up the technology to a broader range of researchers.
369 citations
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TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.
Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …
33,785 citations
Journal Article•
28,685 citations
TL;DR: Authors/Task Force Members: Franz-Josef Neumann* (ESC Chairperson) (Germany), Miguel Sousa-Uva* (EACTS Chair person) (Portugal), Anders Ahlsson (Sweden), Fernando Alfonso (Spain), Adrian P. Banning (UK), Umberto Benedetto (UK).
4,342 citations
TL;DR: Neumann et al. as discussed by the authors proposed a task force to evaluate the EACTS Review Co-ordinator's work on gender equality in the context of women's reproductive health.
Abstract: Authors/Task Force Members: Franz-Josef Neumann* (ESC Chairperson) (Germany), Miguel Sousa-Uva* (EACTS Chairperson) (Portugal), Anders Ahlsson (Sweden), Fernando Alfonso (Spain), Adrian P. Banning (UK), Umberto Benedetto (UK), Robert A. Byrne (Germany), Jean-Philippe Collet (France), Volkmar Falk (Germany), Stuart J. Head (The Netherlands), Peter Jüni (Canada), Adnan Kastrati (Germany), Akos Koller (Hungary), Steen D. Kristensen (Denmark), Josef Niebauer (Austria), Dimitrios J. Richter (Greece), Petar M. Seferovi c (Serbia), Dirk Sibbing (Germany), Giulio G. Stefanini (Italy), Stephan Windecker (Switzerland), Rashmi Yadav (UK), Michael O. Zembala (Poland) Document Reviewers: William Wijns (ESC Review Co-ordinator) (Ireland), David Glineur (EACTS Review Co-ordinator) (Canada), Victor Aboyans (France), Stephan Achenbach (Germany), Stefan Agewall (Norway), Felicita Andreotti (Italy), Emanuele Barbato (Italy), Andreas Baumbach (UK), James Brophy (Canada), Héctor Bueno (Spain), Patrick A. Calvert (UK), Davide Capodanno (Italy), Piroze M. Davierwala
3,879 citations