An intense beam free-electron laser amplifier operating at 35 GHz

The millimeter-wave free-electron laser is a relativistic fast-wave device that offers the possibility of reaching extremely high powers (10/sup 9/ W) at high efficiencies. Operating as an amplifier in the collective regime, this device offers the capability of very high gain with a broad instantaneous gain-bandwidth, is broadly tunable, and can have intrinsic efficiencies of order 10%. Previous results have been reported for this device operating in a superradiant configuration, that is as an amplifier of spontaneous emission. In that configuration, it has produced a record power of 75 MW at a frequency of 70 GHz with 6% experimental efficiency in a 15 nsec pulse, and has demonstrated tunability of this emission at high power over the entire range 25-100 GHz. In this mode of operation, the free-electron laser has also demonstrated the unique capability to produce air breakdown in full atmospheric pressure air with intense millimeter-wave emission