Author: Toyokawa, H.
Paper Title Page
MOOBA03 Development of a High-power Coherent THz Sources and THz-TDS System on the basis of a Compact Electron Linac 37
  • M. Kumaki, K. Sakaue, M. Washio
    RISE, Tokyo, Japan
  • R. Kuroda, H. Toyokawa, K. Yamada
    AIST, Tsukuba, Ibaraki, Japan
  The high-power terahertz time-domain spectroscopy (THz-TDS) has been developed on the basis of a compact S-band electron linac at AIST, Japan. It is strongly expected for inspection of dangerous materials in the homeland security field. The linac consists of a photocathode rf-gun, two acceleration tubes and a magnetic bunch compressor. The 40 MeV, 1 nC electron bunch is generated and compressed to less than 1 ps. THz radiations are generated in two methods with the ultra-short bunch. One is THz coherent synchrotron radiation (CSR). The other is THz coherent transition radiation (CTR). In the preliminary experiment, it was observed that the focused CTR had the donut profile in a transverse fields due to its initial radial polarization, so that it made Z-polarization. In case of the THz-TDS experiment, CTR was controlled to linearly polarization with the polarizer and focused to an EO crystal to obtain a THz temporal waveform which leads to THz spectrum with Fourier transform. The timing measurement between CTR and a probe laser was realized with OTR using a same optical photodiode. In this conference, we will describe details of our linac and results of the THz-TDS experiment.  
slides icon Slides MOOBA03 [3.342 MB]  
MOPPP006 Inverse Cherenkov Radiation based on Smith-Purcell Effect 577
  • K. Kan, T. Kondoh, K. Norizawa, A. Ogata, J. Yang, Y. Yoshida
    ISIR, Osaka, Japan
  • M. Hangyo
    ILE Osaka, Suita, Japan
  • R. Kuroda, H. Toyokawa
    AIST, Tsukuba, Ibaraki, Japan
  Inverse Cherenkov radiation based on Smith-Purcell effect using metamaterial was investigated. A metallic grating and picosecond electron bunch of 27 MeV beam energy from a thermionic DC gun and linac were used for the inverse radiation. The frequency spectra in terahertz (THz) range were measured by a Michelson interferometer experimentally. Peaks of discrete component in the spectra shifted continuously according to the radiation angles, e. g. discrete peak changing from 0.117 to 0.085 THz with radiation angle along the electron bunch from 102 to 134 degree (backward) using a 2-mm-period metallic grating. In this presentation, experiment using another electron bunch generated by a photocathode RF gun linac will be reported.  
THPPR057 Feasibility Study Gamma-induced Positron Annihilation Lifetime Spectroscopy in an Electron Storage Ring 4103
  • Y. Taira, H. Toyokawa
    AIST, Ibaraki, Japan
  • M. Adachi, M. Katoh, S. Tanaka
    UVSOR, Okazaki, Japan
  • N. Yamamoto
    Nagoya University, Nagoya, Japan
  Funding: This work was supported by Grants-in-Aid for Scientific Research (22360297) and Grant-in-Aid for JSPS Fellows (235193).
Positron annihilation lifetime spectroscopy (PALS) has proved to be very sensitive tool to characterize materials and study defects. However PALS has been restricted to thin samples because of the limited range of positrons in materials. We have developed new techniques for PALS, in which laser Compton scattered (LCS) gamma rays are used to produce positrons inside materials via pair production. Ultra-short gamma ray pulse source* with pulse width of 5 ps (FWHM) generated by 90-degree collision LCS was applied to PALS for the first time. The short pulse width of the gamma-rays that is negligible compared to estimated positron lifetime (100 ps to ns range) is essential to PALS. The experiment was carried out at the UVSOR-II electron storage ring, a 750 MeV synchrotron light source. The positron annihilation lifetime, 199 ± 10 ps, in a bulk sample of lead was successfully measured by using the ultra-short gamma ray pulse.
* Y. Taira, et al., Nucl. Instr. And Meth. A 637 (2011) S116.
THPPR070 Development of Multi-collision Laser Compton Scattering X-ray Source on the Basis of Compact S-band Electron Linac 4139
  • R. Kuroda, M. Koike, E. Miura, Y. Taira, H. Toyokawa, K. Yamada, E. Yamaguchi
    AIST, Tsukuba, Ibaraki, Japan
  • M. Kumaki
    RISE, Tokyo, Japan
  A compact hard X-ray source via laser Compton scattering is required for biological, medical and industrial science because it has many benefits about generated X-rays such as short pulse, quasi-monochromatic, energy tunability and good directivity. Our X-ray source is conventionally the single collision system between an electron pulse and a laser pulse. To increase X-ray yields, we have developed a multi-collision system with a multi-bunch electron beam and a laser optical cavity. The multi-bunch electron beam has already been generated from a Cs-Te photocathode rf gun system using a multi-pulse UV laser. The laser optical cavity have developed like a regenerative amplification including the collision point between the electron pulse and the laser pulse which is based on the Ti:Sa laser with a mode-locked frequency of 79.33 MHz. In this preliminary experiment, the modulated seed laser pulses were generated and leaded to the cavity, so that laser build-up amplification was performed in the cavity length of 3.78 m with two seed pulses. In this conference, we will describe the results of preliminary experiments for the multi-collision system and future plans.