Mode competition and control in free-electron-laser oscillators

Abstract

The problem of longitudinal mode competition in free-electron lasers is addressed. It is shown that for small enough ratios of the current to output coupling coefficient many single-mode states are possible. However, the time required to reach these states becomes extremely long for typical devices. Before reaching a single-mode state the radiation field becomes relatively constant in amplitude with modulations of its phase. Finally, a simple method for reaching the stable single-mode state with maximum efficiency is suggested.