Message archive‎ > ‎

Self-Introduction / ごあいさつ

posted Aug 22, 2016, 12:00 AM by PARC Osaka University   [ updated Aug 22, 2016, 12:03 AM ]
My name is Kazuto Yamauchi and I am a new member at the Photonics Center. “Light” for me is X-rays and, therefore, I would like to describe some of the developments in X-ray optics while telling you a little about myself.
X-rays were discovered in 1895 by Wilhelm Röntgen. In 1912, less than twenty years later, Max von Laue discovered the diffraction of X-rays by zinc sulfide crystals, and the following year William H. and William L. Bragg, father and son, presented Bragg’s law. These brilliant achievements gave us light that enabled humans to see atoms, the greatest beneficiary of which is the field of crystal structure analysis. A hundred years later, the U.N. General Assembly proclaimed 2014 to be the International Year of Crystallography, showing just how much X-rays have contributed to crystallography. In the meantime, optics and crystallography have grown immensely, through mutual stimulation, and have dramatically improved the performance of light sources. Higher throughput has been the greatest need for crystal structure analysis, and particularly for the structural analysis of proteins. X-rays in the form of synchrotron radiation sources have shown rapid advancements in brilliance since around 1990. As a result, X-rays acquired the byproduct spatial coherence, which had not been particularly needed for crystal structure analysis, and a new discipline called coherent X-ray optics was born at synchrotron radiation facilities such as SPring-8. While it is somewhat misleading to say, their function as a tool for viewing matter may have brought X-rays back to the forefront of science.
I was a newcomer to the field at this time, working to develop mirrors based on precision machining and metrology for preserving coherence in the light source. We became the first in the world to successfully achieve diffraction-limited focusing and imaging. We also developed a technique for measuring wavefronts based on wave optics and an adaptive optical system for correcting deformations in the wavefronts, and achieved X-ray scanning microscopy with a sub-10 nm spatial resolution and coherent diffraction microscopy approaching a spatial resolution of 1 nm. I take great pride in having contributed in some small way to the advancement of X-ray microscopy based on synchrotron radiation.
Now, synchrotron X-rays have been successfully developed into an X-ray free-electron laser. X-ray FEL facilities are currently installed at two locations: the Stanford Linear Accelerator Center in America and the Riken Harima Branch in Japan. These ultrashort pulse lasers produce wavelengths covering the hard X-ray region, with a pulse duration of femtoseconds. The peak intensity of the beam approaches 10 billion times that of SPring-8. It is a dream light source that is in the process of developing entirely new X-ray sciences. The X-ray mirrors fabricated with our method are called Osaka Mirrors and have been installed at both facilities in the U.S. and Japan. A venture company financed by Osaka University Venture Capital (OUVC) ships the mirrors worldwide, and advanced development of the mirrors is now undertaken by postdoctoral researchers.
Recently we succeeded in observing two-photon absorption with Japan’s X-ray FEL SACLA, using a beam focused down to 50 nm. K emissions were observed when exciting germanium with 5.6-keV X-rays. The intensity of the K fluorescence was essentially proportional to the square of the exciting X-ray intensity. Energy of 11.1 keV was necessary for exciting the Ge K-shell, and there was no intermediate state for two-stage excitation. In fact, the two 5.6 keV photons were absorbed simultaneously with no intermediate state, transferring 11.1 keV of energy to the K-shell electron. The second photon acts within a few hundred zeptoseconds from the first, before the ripples of the first photon have even subsided. This is the first observation of its kind in the X-ray region.
I have continued research on coherent X-ray optics and have been involved in the development of various X-ray devices. However, everything I have done to this point academically has been in optics rather than photonics. If it were not for X-ray FEL making nonlinear optics experiments possible in the X-ray region, I would have been hesitant to join the Photonics Center. This is an exciting area with boundless potential.
As a new member, I hope to contribute to research in photonics in the X-ray region, as well as in surface generation and the like for photonic materials using my specialty of precision machining. But I will cut my self-introduction off here before this gets too lengthy.

August 22, 2016
Kazuto Yamauchi, Professor
Division of Precision Science and Technology and Applied Physics
Graduate School of Engineering
Osaka University

山内 和人  教授