Multimode theory of free-electron laser oscillators

The nonlinear self-consistent theory of short-pulse free-electron laser oscillators can now be extended to include transverse diffraction within the optical resonator mode. The theory provides efficient solutions to the three-dimensional parabolic-wave equation coupled to the Lorentz force equation. The method is general enough to include arbitrary magnet designs, optical mirror arrangements, and driving currents. New mode structures are predicted which should be observed in future experiments at Stanford University.