Ponderomotive phase evolution in short-pulse FEL oscillators operating in the limit-cycle region

Abstract

We have investigated the limit-cycle region of a short-pulse free electron laser (FEL) oscillator system. Using properly defined collective phase variables, we describe the electron dynamics and the phase evolution of the optical field in the limit-cycle region. In this research, we have observed that electrons can be detrapped from the ponderomotive bucket due to the spatial variation of the optical field, and we concluded that the limit-cycle oscillation of the short-pulse FEL oscillator system is a consequence of the electron detrapping.