A tapered wiggler free-electron laser oscillator has been operated at the 1.6-jum wavelength. By increasing the spacing between the constant wavelength wiggler magnets along the wiggler, a magnetic field taper is created. The increased spacing causes the field on-axis to fall, thereby decreasing the amplitude of the electron's oscillation in the wiggler. This shortens the electron's path length, which if appropriately adjusted maintains a constant phase between the electron oscillation and the optical wave. This allows the electrons to stay in resonance with the optical field for the full length of the wiggler, thus enhancing the extraction efficiency.

© 1984 Optical Society of America

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