N.S. Mirian, B. Maraghechi, and E. Salehi,
   "Efficiency Enhancement of a Harmonic Lasing Free-Electron Laser",
   in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper MOP074, pp. 209-212,
    ISBN: 978-3-95450-134-2,
    doi:10.18429/JACoW-FEL2015-MOP074,
    http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/mop074.pdf, 2015.