G. Marcus

Time-domain measurement of a self-amplified spontaneous emission free-electron laser with an energy-chirped electron beam and undulator tapering

We report the first experimental implementation of a method based on simultaneous use of an energy chirp in the electron beam and a tapered undulator, for the generation of ultrashort pulses in a self-amplified spontaneous emission mode free-electron laser (SASE FEL). The experiment, performed at the SPARC FEL test facility, demonstrates the possibility of compensating the nominally detrimental effect of the chirp by a proper taper of the undulator gaps. An increase of more than 1 order of magnitude in the pulse energy is observed in comparison to the untapered case, accompanied by FEL spectra where the typical SASE spiking is suppressed.

Quasicrystalline Beam Formation in RF Photoinjectors

The recent observation of coherent optical transition radiation at the LCLS has raised serious questions concerning the present model of beam dynamics in RF photoinjectors. We present here an analysis of what we term quasicrystalline beam formation. In this scenario, the low longitudinal temperature, in combination with strong acceleration and temporal rearrangement due to bending, allows the longitudinal beam dimension to become more regular, on the microscopic scale of optical wavelengths, than expected from equilibrium statistical properties. This beam distribution then may then display a strong degree of coherence in its optical transition radiation output. We discuss further experimental investigations of this phenomenon.

Breaking the Attosecond, Angstrom and TV/m Field Barriers with Ultrafast Electron Beams

Recent initiatives at UCLA concerning ultra‐short, GeV electron beam generation have been aimed at achieving sub‐fs pulses capable of driving X‐ray free‐electron lasers (FELs) in single‐spike mode. This scheme uses very low charge beams, which may allow existing FEL injectors to produce few‐100 attosecond pulses, with very high brightness. Towards this end, recent experiments at the Stanford X‐ray FEL (LCLS, first of its kind, built with essential UCLA leadership) have produced ∼2 fs, 20 pC electron pulses. We discuss here extensions of this work, in which we seek to exploit the beam brightness in FELs, in tandem with new developments at UCLA in cryogenic undulator technology, to create compact accelerator/undulator systems that can lase below 0.15 A, or be used to permit 1.5 A operation at 4.5 GeV. In addition, we are now developing experiments which use the present LCLS fs pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table‐top TeV accelerator for frontier high energy physics applica...