Seminars Archive

Advanced free-electron laser schemes at the LCLS

Abstract
X-ray free-electron lasers are flexible machines and the properties of the x-rays can be controlled by manipulating the electron beam by proper undulator devices. At the LCLS tunable polarization was provided by the installation of the Delta undulator. Almost fully circularly polarized X-rays are produced in the 500-1200 eV energy range by combining reverse taper and beam diverting. The installation of a de-chirper system enabled the novel fresh-slice scheme, based on a time-dependent electron bunch trajectory impressed by the transverse wake-field of the de-chirper and subsequent orbit control in the undulator section. Fresh slice provides pulse duration control down to few femtoseconds and enables a new FEL multi-color scheme capable of producing multiple fully saturated pulses, with independent control over color separation, delay and beam pointing. True zero delay between the pulses can also be achieved with this scheme. Fresh-slice self-seeding has also been demonstrated and is a viable scheme to combine self-seeding and polarization control in the soft x-rays. Generation of ultra-intense coherent single spikes and pairs of single spikes is under investigation. The fresh-slice scheme can also increase the multiplexing capability of an FEL facility without impact on the beam rate for each experiment.