Mode Structure Of A Low-Gain Low-Voltage Free-Electron Laser

F. A. Dolezal; R. J. Harvey; A. J. Palmer; R. W. Schumacher

doi:10.1117/12.947119

16 February 1984 Mode Structure Of A Low-Gain Low-Voltage Free-Electron Laser

F. A. Dolezal, R. J. Harvey, A. J. Palmer, R. W. Schumacher

Proceedings Volume 0453, Free-Electron Generators of Coherent Radiation; (1984) https://doi.org/10.1117/12.947119
Event: Free-Electron Generators of Coherent Radiation, 1983, Orcas Island, United States

Abstract

A test-model free-electron laser, FEL, has been operated at voltages from 120 to 280 kV. The laser has a 2-cm wiggler period and utilizes a linearly polarized wiggler. The resonator is composed of a 1.75-cm-dia circular waveguide coupled to 8.89-cm-dia spherical mirrors. The beam current is about 15 A and the FEL operates at near threshold. The theoretical gain exceeds the measured cavity losses (10 to 30 percent per pass) only for the higher Q modes. The most intense emission occurs at frequencies near the waveguide cutoff of 10.2 GHz, where we estimate the emitted power to be saturated at 10 to 100 kW. Signals have been observed to last for over 10 ps. This lower frequency mode, (which we presume is the backward TE11 FEL wave), dominates. Radiation is reproducibly observed to appear during periods when the voltage corresponds qualitatively to resonator modes; with each mode usually occurring twice during the pulse, e.g. during the rise and fall of the voltage. The rate of change of the voltage affects the gain under these circumstances and the signal is quenched if the change exceeds about 4% per ps. Harmonic frequencies are also observed at frequencies near to, but not on, the forward-wave branch of the FEL-dispersion curve. The intensity of the third harmonic (31 GHz) is on the order of 44 W.

Citation Download Citation

F. A. Dolezal, R. J. Harvey, A. J. Palmer, and R. W. Schumacher "Mode Structure Of A Low-Gain Low-Voltage Free-Electron Laser", Proc. SPIE 0453, Free-Electron Generators of Coherent Radiation, (16 February 1984); https://doi.org/10.1117/12.947119

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