Optical harmonics are naturally generated within free electron lasers (FELs) by the nonuniform axial motion of the electrons within the magnetic undulator. Although far weaker than the optical beam produced at the fundamental lasing frequency, they can provide useful amounts of coherent power at shorter wavelengths. However, UV harmonics can degrade dielectric optics by producing color centers which must be precluded in high power FELs. Up to this time, adequate verification of various theoretical predictions has not been possible because of limited experimental data. To address this problem, we conducted a series of experiments with the Los Alamos infrared FEL oscillator to characterize the power and spatial distribution of the measurable harmonic orders (1, 2, 3, and 5) as a function of electron-beam, undulator, and resonator parameters. The FEL operated at a fundamental wavelength from 10 to 12 μm with a ~20 MeV electron beam with peak current varying from 200 to 500 A.

© 1989 Optical Society of America

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