Demonstration of a new free-electron-laser harmonic interaction

Abstract
The first experimental demonstration of a harmonic free-electron-laser amplifier utilizing a periodic position instability is described for a planar wiggler configuration. The interaction occurs at the even harmonics of the fundamental. A maximum gain of 7 dB was observed over a frequency band ranging from 14 to 15 GHz. The experimental results are compared with predictions from the three-dimensional simulation code w i g g l i n with excellent agreement. Improvements due to a tapered wiggler for this interaction are discussed.