P.M. Anisimov,
   "Quantum Nature of Electrons in Classical X-ray FELs",
   in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper TUP006, pp. 338-341,
    ISBN: 978-3-95450-134-2,
    doi:10.18429/JACoW-FEL2015-TUP006,
    http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/tup006.pdf, 2015.