Lienard-Wiechert Potentials and the Method of Images in an RF Free   Electron Laser Photoinjector
  Based on Lienard-Weichert retarded potentials and the potential due to the image of charges on the cathode, a rigorous relativistic description of the beam transport inside the RF-photoinjector is presented. The velocity dependent effects are taken into account. Simulations are presented for parameters of the "ELSA" photo-cathode 
W. Salah, R.M. Jones