High-gain harmonic generation free-electron laser with variable wavelength.

The external seed of the high-gain harmonic generation (HGHG) free-electron laser (FEL) determines the wavelength of the output radiation. Therefore, the tunability of such a laser depends upon the tunability of the seed. In this paper, we present and discuss an alternative scheme for the tunable HGHG FEL wherein the seed's wavelength is fixed and the variations in the wavelength of radiation are achieved by tuning the accelerator. As an illustration, we apply our proposed scheme to the deep ultraviolet free electron laser (DUV FEL) at Brookhaven National Laboratory demonstrating the ability to attain about a +/-10% variation in the wavelength's tuning range.