A. Gover, C. Emma, A. Friedman, R. Ianconescu, and P. Musumeci, "Conceptual Theory of Spontaneous and Taper-Enhanced Superradiance and Stimulated Superradiance", in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper WEP085, pp. 746-751, ISBN: 978-3-95450-134-2, doi:10.18429/JACoW-FEL2015-WEP085, http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/wep085.pdf, 2015.