SPring-8, the large synchrotron radiation facility

Scientists of RIKEN (President, Ryoji Noyori) and Nagoya University (President, Michinari Hamaguchi) have developed a microscopic technique with an ultrahigh spatial resolution of as fine as 0.54 angstrom (Å)^*1 using a nonlinear optical phenomenon^*2 in the X-ray region. This resolution corresponds to 1/380 of a wavelength (206 Å), which cannot be achieved by conventional methods. The achievement of this study was obtained by the group of Kenji Tamasaku (Senior Research Scientist) and Tetsuya Ishikawa (Chief Scientist) of the Coherent X-Ray Optics Laboratory of RIKEN SPring-8 Center (Director, Tetsuya Ishikawa) and Eiji Nishibori (Associate Professor) of School of the Engineering, Nagoya University.

Since the optical microscope was invented at the end of the 16th century, improving its resolution has been a top priority. However, Dr. Abbe of University of Jena (Germany) demonstrated in 1878 that the maximum spatial resolution is in principal approximately a half of the wavelength and that a substance smaller than this cannot be observed. Although researchers worldwide have tried various methods to overcome this constraint, a spatial resolution of approximately a tenth of the wavelength is still the limit even today. At this spatial resolution, it is impossible to directly observe how electrons in a substance respond to light (the optical response), in other words, the reason why a substance has a particular color.

To solve this problem, the scientists of the above research group developed a new microscopic technique with an ultrahigh spatial resolution based on a nonlinear optical phenomenon in the X-ray region, in which one "parent" photon^*3 is divided into a big sister photon and a little sister photon, using the RIKEN Synchrotron Radiation Physics Beamline (BL19LXU) at SPring-8, which can radiate extremely intense X-rays. In this method, the little sister photon with a long wavelength acts on a substance and the big sister photon observes the response. In this way, the sister photons work cooperatively. The big sister photon can observe the phenomenon at an ultrahigh spatial resolution because it is an X-ray photon. In this study, X-rays (parent photons) were irradiated on a diamond sample, and they succeeded in observing the behavior of each internal electron in the extreme-ultraviolet region^*4 where the little sister photon exists.

The results of this study indicate the possibility of microscopes with a spatial resolution that is far beyond the limit expressed in terms of the wavelength. It is hoped that we will be able to directly observe the optical response of a substance to obtain a deeper understanding of substances and to contribute to the sophisticated use of microscopes through further advances in measurement technology in the future.

This research was supported by the JST Basic Research Programs for individual researchers [Precursory Research for Embryonic Science and Technology (PRESTO)] project "Innovative Use of Light and Materials/Life" (Research Supervisor: Hiroshi Masuhara, Specially Appointed Professor at Nara Institute of Science and Technology and Chair Professor of National Chiao Tung University in Taiwan) under the title "Investigation of local optical response using X-ray nonlinear diffraction" (Scientist: Kenji Tamasaku). The results were published online in the scientific journal Nature Physics on 17 June 2011.

Publication:
"Visualizing the local optical response to extreme-ultraviolet radiation with a resolution of λ/380"
Kenji Tamasaku, Kei Sawada, Eiji Nishibori and Tetsuya Ishikawa
Nature Physics (2011), published online 17 July 2011