%\cite{Blau:FEL2015-WEP008} \bibitem{Blau:FEL2015-WEP008} J.~Blau, K. R.~Cohn, and W.B.~Colson, \textquotedblleft{Four-Dimensional Models of FEL Amplifiers and Oscillators}\textquotedblright, % in \emph{Proc. FEL2015}, WEP008, pp. 607--614, % in \emph{Proc. FEL2015}, Daejeon, Republic of Korea, August 2015, paper WEP008, pp. 607--614, in \emph{Proc. 37th International Free Electron Laser Conference (FEL2015)}, Daejeon, Republic of Korea, August 2015, paper WEP008, pp. 607--614, ISBN: 978-3-95450-134-2, \url{http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/wep008.pdf}, doi:10.18429/JACoW-FEL2015-WEP008, 2015.