Development of a modified wiggler for higher harmonic lasing of a free-electron laser

Abstract A modified wiggler, with enhanced harmonic fields, was developed for free-electron laser higher harmonic lasing. The harmonic wiggler field was produced by arranging high-permeability shims in the gap spacing of a four-block-per-period Halbach design wiggler. By this method, the 3rd harmonic wiggler field exceeded 18% of the fundamental field. The phasing of the harmonic field could be also controlled by the positioning of the shims.