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The Birth of the Most Intense X-ray Laser Beam in the World (Press Release)

Release Date
17 Dec, 2012
- A focusing mirror with atomic level surface precision enabled realization of a highly condensed beam with a diameter of one micrometer -

Japan Synchrotron Radiation Research Institute (JASRI)
Osaka University
The University of Tokyo
Japan Science and Technology Agency

Main points of the research
• Development of a large focusing mirror, 420mm in length, with atomic-level surface precision
• Realization of an extreme-strength X-ray free-electron laser microbeam (4 × 104 times greater intensity than previous beams)
• Establishment of base technologies instrumental for tracking down the causes of diseases and developing novel drugs: e.g. a microscope system capable of recording snapshots at atomic-level resolution

The collaborative research conducted by four research organizations- JASRI (president: Tetsuhisa Shirakawa), Osaka University (president: Toshio Hirano), the University of Tokyo (president: Junichi Hamada), and RIKEN (president: Ryoji Noyori)- successfully realized the most powerful X-ray laser microbeam in the world at X-ray free-electron laser (XFEL) facility SACLA*1 (pronounced “sakura” in Japanese), whereby a set of focusing mirrors with atomic-level surface precision played an integral role.

Effective utilization of the high intensity XFEL available at SACLA is expected to pave the way for the future development of an ultra-high-resolution microscope system that will enable, for example, instantaneous capture of steric configuration of proteins on a molecule-by-molecule basis. This endeavor necessitates the development of a novel optical element for collecting as many XFEL rays as possible to generate a focused beam with extreme intensity to be used for highly efficient illumination of a very tiny target for observation. Up to the present, however, such an optical element- usable stably under exposure to intense XFEL illumination, and with high focusing efficiency- has not been available, hindering the generation of a precisely focused, ultra-high-intensity beam.

The research group developed a focusing mirror, the reflective surface of which is ellipsoidal, to bring X-rays to a focal point. As the wavelength of an X-ray is very short, comparable to the size of an atom, even the tiniest bumps and dips on a mirror surface can destructively affect the reflected rays. Therefore, the mirror requires the pursuit of extreme smoothness down to the atomic level and a precisely controlled surface profile to bring X-rays efficiently to a focal point. To this end, the research group took advantage of two precision processing techniques- ELID (Electrolytic In-process Dressing) grinding,*2 developed at RIKEN, and the EEM (Elastic Emission Machining) method,*3 developed at Osaka University- to manufacture a large (420mm in length) mirror with extreme surface precision controlled to the atomic level. The implementation of the focusing mirror developed in this research for the SACLA system successfully generated an XFEL microbeam with a theoretical focal point size (horizontal: 0.95 μm, vertical: 1.20 μm). The use of the focusing mirror demonstrated the feasibility of a 4 × 104 fold increase in light density of the XFEL beam, achieving the world’s most highly concentrated light field (6 × 1017W/cm2)*4 in terms of XFEL use.

The extreme intensity XFEL microbeam imaging technique developed in this research has already been put to introductory use in certain studies aiming at elucidating the structure of monocellular organisms and compound proteins. Based on this technique, a novel microscope system is also being studied in view of capturing time-resolved images of the steric structure of proteins, which is expected to promote a causal understanding of diseases and development of new drugs.

The results reported here were gained through collaborative research among the following researchers and groups: Dr. Hirokatsu Yumoto (researcher, JASRI), Dr. Haruhiko Ohashi (associate chief scientist, JASRI), Dr. Kensuke Tono (associate chief scientist, JASRI), Prof. Kazuto Yamauchi (Graduate School of Engineering, Osaka University), Associate Prof. Hidekazu Mimura (Dept. of Precision Engineering, The University of Tokyo), the Beam Line Research and Development Group (group director: Dr. Makina Yabashi) of XFEL Research and Development Division at RIKEN SPring-8 Center (director: Dr. Tetsuya Ishikawa), and the research group led by Dr. Hitoshi Omori μ. The research results were published in the online version of Nature Photonics (a scientific journal) on the December 17, 2012 (JST).

"Focusing of X-ray free electron laser pulses with reflective optics"
Hirokatsu Yumoto, Hidekazu Mimura, Takahisa Koyama, Satoshi Matsuyama, Kensuke Tono, Tadashi Togashi, Yuichi Inubushi, Takahiro Sato, Takashi Tanaka, Takashi Kimura, Hikaru Yokoyama, Jangwoo Kim, Yasuhisa Sano, Yousuke Hachisu, Makina Yabashi, Haruhiko Ohashi, Hitoshi Ohmori, Tetsuya Ishikawa and Kazuto Yamauchi
Nature Photonics 7, 43-47 (2013), Published online 16 December 2012


Fig.1 Focused X-ray free-electron laser beam with ultra high intensity opens up new domains of application
Fig.1 Focused X-ray free-electron laser beam
with ultra high intensity opens up new domains of application

The extreme energy density of the XFEL beam from SACLA can be further augmented by a factor up to 4 × 104 through the use of a condensing mirror system. The XFEL beam thus augmented has an extraordinary intensity that humans have never experienced, and is expected to open up a variety of novel scientific domains.

Fig.2 The design of the mirror’s shape, and the shape error observed between the designed and the actual mirror profile.
Fig.2 The design of the mirror’s shape, and the shape error observed
between the designed and the actual mirror profile.

Osaka University and RIKEN joined forces to achieve extreme smoothness in the surface of the large focusing mirror, limiting its surface roughness down to an atomic size level.

Fig.3 High precision alignment adjusting equipment for the focusing mirror
Fig.3 High precision alignment adjusting equipment for the focusing mirror

The focusing mirror, operated inside a vacuum housing, needs a rigorous special posture control. After being adjusted to a specific position and angle, it must come to a rest to a degree of precision better than 10-4 in terms of the angle.

Fig. 4 Intensity distribution of focused X-ray free-electron laser beam
Fig. 4 Intensity distribution of focused X-ray free-electron laser beam

According to measurements, the world’s most intense XFEL beam, after being focused, is confirmed to attain the size of 0.95 μm in the horizontal direction and 1.20 μm in the vertical direction.

Fig. 5 Signature of evaporation caused by irradiation of extremely intensely focused X-ray free-electron laser beam.
Fig. 5 Signature of evaporation caused by irradiation of
extremely intensely focused X-ray free-electron laser beam.

Because of the extreme intensity of the focused beam, irradiated spots on the surface of the material evaporate instantly. The figure shows an electron microscope image indicating the irradiated spots on a Pt sample. The intensity of the focused beam at each spot is: (a) 0.09μJ, (b) 0.30μJ, (c) 7.6μJ.
(a): The signature of evaporative removal has a size comparable to that of the focused beam. Adjustment of irradiation intensity enables the evaluation of the size of the focused beam.
(b and c): Further augmentation of beam power gives rise to an explosive evaporation of the material, involving the immediate neighborhood of the irradiated spot.

*1 X-ray free-electron laser (XFEL) facility “SACLA”

SACLA is the moniker for the facility, derived from SPring-8 Angstrom Compact free-electron LAser. The RIKEN-operated facility, located in Harima Science Garden City (Hyogo prefecture), started its services in March 2012. The X-ray free-electron laser is characterized by its ability to produce very short wavelengths of light, comparable to X-rays, generated in a vacuum by electrons extracted from matter (free electrons). The XFEL light has a unique combination of the following four features:
(1) Extremely short wavelengths comparable to an atom, which is the minimum constituent unit of matter, typically with such a minute size as 10-9m (i.e. an X-ray is produced).
(2) Spatially perfectly coherent light (i.e. laser light).
(3) Exceptionally high intensity (109 times brighter than SPring-8*5)
(4) Ultra short pulse source (as instantaneous as a camera flash, and the pulse width is as extremely short as 10-14 sec).

*2 ELID (Electrolytic In-process Dressing) grinding
A highly efficient precision mirror finishing technique developed at RIKEN. The grinding process typically uses a grind stone (a working tool) that includes very hard particles, such as diamond particles, to grind the target material by rotating the tool at high speed. Conventional grinding techniques have inherent limitations: abrasive grains at the surface gradually become worn and clogged with usage, leading to a loss of sharpness in cutting edges. ELID grinding uses a grinding stone made of a mixture of conductive grains (such as metallic materials) and abrasive grains. This combination enables the maintaining of sharp cutting edges throughout the whole process, by removing conducting particles from the tool surface through the application of an electric field during the course of the grinding operation. The ELID process can perform stable and fast precision mirror finishing thanks to the tiny abrasive grains and the surface renewal mechanism.

*3 EEM (Elastic Emission Machining)
An ultra precision surface finishing technique developed at Osaka University, which enables the removal of individual atoms by leveraging chemical reactions between the target solid surface and tiny particles. With precise control of the amount of reactive tiny particles fed onto the material surface, this technique can achieve any shape desired. This machining technique harnesses chemical reactions and does not apply mechanical power to the material surface, enabling achievement of atomic-level smoothness without affecting the atomic arrangement of the material surface.

*4 Intensity of focused light (6 × 1017W/cm2)
The magnitude of light condensation is expressed in Watts per square centimeter (W/cm2). This represents the quantity of energy (in Watts) that passes through an area of one square centimeter. For example, if a square hot plate, 30 × 30cm (or 900cm2 in terms of area), for standard home use generates 1000 Watts of heat energy, its energy density is approximately 1 W/cm2. The ultra high intensity microbeam reported here has approximately 60 × 1016 greater intensity than a standard home hot plate.

*5 SPring-8
A RIKEN facility located in Harima Science Garden City (Hyogo prefecture) is capable of producing the world's highest intensity synchronous radiation. The management and promotion of utilization of this facility are undertaken by JASRI. The name “SPring-8” comes from “Super Photon ring-8GeV.” An electron flying at nearly the speed of light, if deflected from its original trajectory through the effect exerted by a magnet, emits an electromagnetic wave in a direction tangential to its trajectory, which is called radiation light (or synchrotron radiation). At present, there are three “3rd Generation” large scale synchronous radiation facilities in the world: SPring-8 (Japan), APS (USA) and ESRF (France). The acceleration energy available at SPring-8 (8 billion electron volts) enables the provision of an extremely wide spectrum of radiation light: from far infrared to visible, vacuum ultraviolet, and soft X-ray up to hard X-ray. SPring-8 provides a theater for collaborative works involving researchers inside and outside Japan, and the research conducted at this facility cover such diverse areas as material science, geoscience, life science, environmental science, and various applications in industrial sectors.

For more information, please contact:
  Dr. Hirokatsu Yumoto (JASRI)
   E-mail : mail1

  Prof. Kazuto Yamauchi (Department of Applied Physics, Osaka University)
   E-mail : mail2

  associate Prof. Hidekazu Mimura (Department of Precision Engineering, The University of Tokyo)
   E-mail : mail3