Exotic radiation from a photonic crystal excited by an   ultra-relativistic electron beam
  We report the observation of an exotic radiation (unconventional Smith-Purcell radiation) from a one-dimensional photonic crystal. The physical origin of the exotic radiation is direct excitation of the photonic bands by an ultra-relativistic electron beam. The spectrum of the exotic radiation follows photonic bands of a certain parity, in striking contrast to the conventional Smith-Purcell radiation, which shows solely a linear dispersion. Key ingredients for the observation are the facts that the electron beam is in an ultra-relativistic region and that the photonic crystal is finite. The origin of the radiation was identified by comparison of experimental and theoretical results. 
N.Horiuchi, T.Ochiai, J.Inoue, Y.Segawa, Y.Shibata, K.Ishi, Y.Kondo,   M.Kanbe, H.Miyazaki, F.Hinode, S.Yamaguti, K.Ohtaka