The mode structure of a tapered wiggler free-electron laser (FEL) stable oscillator is investigated using an axisymmetric physical optics code which accounts for diffraction, nonuniform gain media, refraction, and arbitrary mirror configurations and reflectivities. Figure 1 shows the evolution of TEM10 and TEM10 mode content, as a plane polarized optical beam is circulated in symmetric resonators of various lengths. Each cavity has mirrors of radius 1.8 w/ located at the ends of the wiggler, where w is the 1/e amplitude point for the initial 0-0 pump beam.

© 1982 Optical Society of America

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