The performance of a two-mirror resonator with holes for out-coupling has been examined in a previous study in which the FEL gain was neglected, but the geometrical effect of the wiggler aperture was included in the optical calculation. The phenomenon of mode degeneracy was found to occur, that has serious implications for the stability of performance when the FEL gain is included. We have developed a FEL oscillator code based on "TDA", a three-dimensional FEL amplifier code, to study the mode characteristics in the presence of an FEL. We find that the interaction of the radiation and the FEL has an important, and positive, impact on the mode-profile and related cavity performance parameters. In particular, mode degeneracy is not expected to be a serious problem for reasonable FEL oscillator designs. © 1992.
Krishnagopal, S., Xie, M., Kim, K. J., & Sessler, A. (1992). Three-dimensional simulation of a hole-coupled FEL oscillator. Nuclear Inst. and Methods in Physics Research, A, 318(1–3), 661–664. https://doi.org/10.1016/0168-9002(92)91135-V