Gamma-ray free-electron lasers: Quantum fluid model H. M. Silva, A. Serbeto, R. M. O. Galvão, J. T. Mendonça and L. F. Monteiro EPL, 108 6 (2014) 65002 Published online: 09 January 2015 DOI: 10.1209/0295-5075/108/65002