Sideband suppression by an intracavity optical filter in the Los Alamos free-electron laser oscillator

Experiments at the Los Alamos free-electron laser oscillator were performed with a 7.35% (delta gamma /sub r//delta gamma /sub r/) tapered wiggler. Multilayer dielectric mirrors with wavelength-dependent reflectivity and phase shift functions were used to provide high reflectivity at the fundamental wavelength but to introduce losses at expected sideband wavelengths. The electron-beam energy was varied to tune the fundamental optical wavelength. Experimental measurements are compared with results of 1-d time-dependent simulations. For the particular wiggler, optics, and e-beam conditions of this experiment, spectral sidebands were reduced only with a concomitant reduction of the total optical output of the laser.