• K. Kan, T. Kondoh, T. Kozawa, K. Norizawa, A. Ogata, J. Yang, Y. Yoshida
  ISIR, Osaka

Time resolution of pulse radiolysis, which is a stroboscopic measurement technique, depends on electron bunch length. In order to improve the time resolution, femtosecond electron bunch generation at photocathode rf gun was investigated. A 1.6-cell S-band photocathode rf gun, similar to the Gun IV type at Brookhaven National Laboratory (BNL), was used. The rf gun consisted of a half cell and a full cell. A copper cathode was located in the half cell. The rf gun was driven by femtosecond UV laser pulse (266 nm), which was generated with third-harmonic-generation (THG) of Ti:Sapphire femtosecond laser (800 nm). The longitudinal and transverse dynamics of the electron bunch generated by the UV laser was investigated. The bunch length was measured with the dependence of energy spread on acceleration phase in a linac, which was set at the downstream of the rf gun. Transverse emittance at the linac exit was also measured with Q-scan method.

• T. Kondoh, K. Kan, T. Kozawa, K. Norizawa, A. Ogata, J. Yang, Y. Yoshida
  ISIR, Osaka

Femtosecond electron beam pulse radiolysis which has time resolution of 250 fs was achieved by a Photocathode RF gun LINAC in the ISIR, Osaka University. And geminate ion recombination (charged pair dynamics) in n-dodecane was studied. Kinetics of the Radical cation of n-dodecane was measured. As a result, the existence of the excited-radical cation, and generation of the radical cation via relaxation from the excited-radical cation were suggested. Those new results were obtained in the field of the radiation chemistry by the photocathode RF gun.

• J. Yang, K. Kan, T. Kondoh, Y. Murooka, N. Naruse, K. Tanimura, Y. Yoshida
  ISIR, Osaka
• J. Urakawa
  KEK, Ibaraki

Both ultrafast time-resolved radiolysis and electron diffraction based on photocathode rf electron guns have been developed in Osaka University to reveal the hidden dynamics of intricate molecular and atomic processes in materials. One of the photocathode rf guns has been used successfully to produce a 100-fs high-brightness electron single bunch with a booster linear accelerator and a magnetic bunch compressor. The time resolution of 240 fs was achieved at the first time in the pulse radiolysis. Another photocathode rf gun, which produces directly a near-relativistic 100-fs electron beam, has been developed to construct femtosecond electron diffraction. The megavolt electron diffraction patterns have been observed. The dependences of the emittance, bunch length and energy spread on the radio-frequency (rf) and space charge effects in the rf gun were investigated.