D.F. Ratner, A. Gover, E. Hemsing, A. Marinelli, and A. Nause,
   "Subradiant Spontaneous Undulator Emission through Collective Suppression of Shot Noise",
   presented at the 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper WEC04, unpublished.