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Demonstrated basic technology to map only specific elements with different upper and lower environments, utilizing harmonic generation by X-ray free electron laser

The University of Tokyo
RIKEN
Tokyo University of Science
Institute for Molecular Science
Japan Synchrotron Radiation Research Institute (JASRI)

Overview:

The research group successfully observed nonlinear optical effects (second harmonic generation) of soft X-rays using the X-ray free electron laser, by making use of the facility called SACLA (SPring-8 Angstrom Compact free electron Laser). It was also revealed that this signal generation was amplified by double occurrence of the inner core resonance effect by quantum mechanics calculation of optical properties. This achievement was made it possible by the research group of Associate Professor Iwao Matsuda and Project Professor Hisazumi Akai, both at the Institute for Solid State Physics, the University of Tokyo, in collaboration with Group Director Makina Yabashi of RIKEN, Professor Takahisa Arima of the Graduate School of Frontier Sciences of the University of Tokyo, Associate Professor Masato Kotsugi of Tokyo University of Science, Technical Division Head Eiji Shigemasa of Institute for Molecular Science, Professor Hiroshi Kumigashira of Institute of Materials Structure Science at the High Energy Accelerator Research Organization, and Team Leader Kensuke Tono of the Registered Institution for Facilities Use Promotion, Japan Synchrotron Radiation Research Institute (JASRI).

The research found that selective observation of both the elemental mapping at interfaces and phenomenon that occurs at the interface was possible, by using soft X-ray with element selectivity for the nonlinear optical effect that could observe the interface of materials and the special order in which symmetry was broken. The result proved observation was technically possible. In the future, the outcome of this research is expected to be utilized for various opportunities as a new analysis method of materials with element selectivity added to nonlinear optical signals. The research paper was published in the Physical Review Letters online ( June 1, 2018).

Figure 1: a) Soft X-ray free electron laser experiment conducted at SACLA. The fundamental waves (ω) and the second harmonic waves (2ω) reflected from the specimen were spectrally detected with a diffraction grating. Although b) the fundamental intensity (I ω) was proportional to the incident light intensity (I0) (linear), the second harmonic (I2ω) referred to c) became a quadratic curve (nonlinear). The signal is notably observed at 55 eV which indicates the inner shell resonance energy of Fe element as seen in c) and the signal intensity drastically decreases like d) at 53 eV, that is slightly deviated from 55 eV.
Figure 1: a) Soft X-ray free electron laser experiment conducted at SACLA. The fundamental waves (ω) and the second harmonic waves (2ω) reflected from the specimen were spectrally detected with a diffraction grating. Although b) the fundamental intensity (I ω) was proportional to the incident light intensity (I0) (linear), the second harmonic (I) referred to c) became a quadratic curve (nonlinear). The signal is notably observed at 55 eV which indicates the inner shell resonance energy of Fe element as seen in c) and the signal intensity drastically decreases like d) at 53 eV, that is slightly deviated from 55 eV.

Reference:

  • Journal: Physical Review Letters
  • Title: Element selectivity in second harmonic generation of GaFeO3 by a soft X-ray free-electron laser
  • Author:Sh. Yamamoto, T. Omi, H. Akai, Y. Kubota, Y. Takahashi, Y. Suzuki, Y. Hirata, K, Yamamoto, R. Yukawa, K. Horiba, H. Yumoto, T. Koyama, H. Ohashi, S. Owada, K. Tono, M. Yabashi, E. Shigemasa, S. Yamamoto, M. Kotsugi, H. Wadati, H. Kumigashira, T. Arima, S. Shin, I. Matsuda
  • DOI:https://doi.org/10.1103/PhysRevLett.120.223902
(Published on: Tuesday June 12th, 2018)