title: Efficiency and spectrum enhancement in a tapered free-electron laser amplifier.
abstract: We report the first experimental characterization of efficiency and spectrum enhancement in a laser-seeded free-electron laser using a tapered undulator. Output and spectra in the fundamental and third harmonic were measured versus distance for uniform and tapered undulators. With a 4% field taper over 3 m, a 300% (50%) increase in the fundamental (third harmonic) output was observed. A significant improvement in the spectra with the elimination of sidebands was observed using a tapered undulator. The experiment is in good agreement with predictions using the MEDUSA simulation code.
authors.affiliation: National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: X J
authors.initials: XJ
authors.lastname: Wang
authors.forename: H P
authors.initials: HP
authors.lastname: Freund
authors.forename: D
authors.initials: D
authors.lastname: Harder
authors.forename: W H
authors.initials: WH
authors.lastname: Miner
authors.forename: J B
authors.initials: JB
authors.lastname: Murphy
authors.forename: H
authors.initials: H
authors.lastname: Qian
authors.forename: Y
authors.initials: Y
authors.lastname: Shen
authors.forename: X
authors.initials: X
authors.lastname: Yang