Effects of non-resonant electron velocity components in a second harmonic waveguide free electron laser

As a technique to reduce the size and hence the cost of compact waveguide f ree electron lasers (FELs) operated in the spectrum from microwave to the f ar infrared, a longitudinal interaction mechanism was recently proposed to operate waveguide free electron lasers at the second harmonic. Unlike conve ntional waveguide FELs based on the electron interaction with the transvers e electric field component of the waveguide electromagnetic wave, these sec ond harmonic waveguide FELs have electron velocity components that are not in resonance with the waveguide electromagnetic wave. These non-resonant co mponents were considered to be negligible. In this contribution, we conside r the effects of these non-resonant velocity components on the interaction gain. With a new gain formulation in the small signal regime, it is shown t hat the non-resonant velocity components affect the interaction gain signif icantly. Energy spread effects are then considered and compared to that in conventional waveguide free electron lasers. (C) 1999 Elsevier Science B.V. All rights reserved.