Effect of dispersive optical elements in the Vanderbilt Free-Electron Laser resonator

The Brewster-angle windows used in the optical resonator of the Vanderbilt FEL become dispersive at wavelengths approaching the band-edge near 10 μm. The effect of this dispersion is included in a 1-D FEL simulation code as an integral transform of the optical pulse emerging from the wiggler in each pass of the FEL. sults indicate small amounts of chirp of the optical pulse, as might have been expected beforehand. In addition, the optical-resonator length-desynchronism curve is broadened, and the relatively sharp cutoff of oscillation near exact synchronism predicted by simulations without dispersion becomes a smooth rolloff with dispersion. These results agree with experimental observations.