• M.D. Shinn, S.V. Benson, G. Neil, A.M. Watson
  JLAB, Newport News, Virginia
• R. Lalezari
  ATF, Boulder
• P.J.M. van der Slot
  Twente University, Laser Physics and Non-Linear Optics Group, Enschede

We report the design, and broadly tunable operation, for the first time, of a high average power free-electron laser using edge-outcoupling. Using the FEL in this configuration, we achieved a maximum stable output power of 270W at 2.53 μm, and could tune with an output of 20 W or higher from 0.8 to 4.2 μm. The output was in the form of a continuous train of sub-ps pulses at 4.68 MHz. Measurements of gain, loss, and the output mode are compared with models.