Gamma-ray free-electron lasers: Quantum fluid model
  A quantum fluid model is used to describe the interacion of a nondegenerate cold relativistic electron beam with an intense optical wiggler taking into account the beam space-charge potential and photon recoil effect. A nonlinear set of coupled equations are obtained and solved numerically. The numerical results shows that in the limit of plasma wave-breaking an ultra-high power radiation pulse are emitted at the$\gamma$-ray wavelength range which can reach an output intensity near the Schwinger limit depending of the values of the FEL parameters such as detuning and input signal initial phase at the entrance of the interaction region. 
H.M. Silva, A. Serbeto
physics.plasm-ph