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Experimental Demonstration of an Electromagnetically Pumped Free-Electron Laser with Cyclotron Harmonic Idlers

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Summary rept. Jan 1987-Jun 1988

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A new type of electromagnetically pumped, three-wave free-electron laser FEL has been observed in which cyclotron harmonic waves act as idlers. In this experiment, a powerful electromagnetic pump wave replaced the usual magnetostatic wiggler. The pump wave was generated by a backward wave oscillator 8.4 GHz, 50 MW peak power driven by an intense relativistic electron beam 625 kV, 2 kA, 100 ns. A grating spectrometer was used to scan the microwave frequency spectrum from 50 to 130 GHz, and powerful high-frequency radiation was observed in the form of an array of regularly spaced peaks. The positions of the peaks were observed to vary with the magnitude of the axial guide magnetic field in a manner which agrees with the dispersion relationship omega sub s omega sub w k sub w v sub g k sub s v parallel l Omega sub 0 due to a three-wave FEL interaction in which the cyclotron beam waves act as idler where omega sub s, k sub s and omega sub w, k sub w are the frequency and wave number of scattered and pump waves, Omega sub 0 is the relativistic electron cyclotron frequency, l is the harmonic number, and v parallel is the axial beam velocity. Harmonic numbers l 1 and 5 to 14 are identified while sweeping through the frequency ranges from 7 to 18 GHz and 50 to 130 GHz. The results exhibit excellent agreement with a simple theoretical model of the three-wave interaction.

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  • Lasers and Masers

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