N. Sei, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, \emph{et al.},
   "Development of Coherent Terahertz Wave Sources using  LEBRA and KU-FEL S-band Linacs",
   in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper MOP050, pp. 143-146,
    ISBN: 978-3-95450-134-2,
    doi:10.18429/JACoW-FEL2015-MOP050,
    http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/mop050.pdf, 2015.