Nonlinear interaction between radiation and an electron beam in a free-electron laser oscillator based on a two-frequency wiggler

A two-frequency wiggler was used to enhance the efficiency and the radiation power in a far-infrared free-electron laser oscillator. The interaction between the electron beam and the radiation was numerically studied using multi-particle and multi-pass simulation coding to understand the effect of the two-frequency wiggler, and the wiggler’s frequency ratio parameter was optimized. The influence of the electron beam energy spread was also investigated in the two-frequency wiggler for a monochromatic laser field.