ABSTRACT
As a result of the interaction between the relativistic electron beam and the electromagnetic fields, free-electron laser (FEL) comes to be a highly nonlinear system in which instabilities and chaos can easily be found. In 1988, Riopoulos and Tang (1988) studied the chaotic motion of electrons in a combined field of the wiggler magnetic field, the fundamental mode, and the sidebands. Two years later, Chen and Davidsion(1991) found that the trajectory of an electron in a helical wiggler with an axial guide field could also be chaotic when the electrostatic and magnetic self-fields of the electron beam could not be neglected. However, the optical field chaos which may cause a broadening of the laser spectrum has rarely been considered (Billardon, 1990).
