Mode locking in a free-electron laser amplifier

Abstract

A technique is proposed to generate attosecond pulse trains of radiation from a free-electron laser amplifier. The optics-free technique synthesizes a comb of longitudinal modes by applying a series of spatiotemporal shifts between the copropagating radiation and electron bunch in the free-electron laser. The modes may be phase locked by modulating the electron beam energy at the mode spacing frequency. Three-dimensional simulations demonstrate the generation of a train of 400as pulses at gigawatt power levels evenly spaced by 2.5fs at a wavelength of 124. In the x-ray at wavelength 1.5, trains of 23as pulses evenly spaced by 150as and of peak power up to 6GW are predicted. © 2008 The American Physical Society.