Single-shot electron diffraction using a cold atom electron source

Abstract

Cold atom electron sources are a promising alternative to traditional photocathode sources for use in ultrafast electron diffraction due to greatly reduced electron temperature at creation, and the potential for a corresponding increase in brightness. Here we demonstrate single-shot, nanosecond electron diffraction from monocrystalline gold using cold electron bunches generated in a cold atom electron source. The diffraction patterns have sufficient signal to allow registration of multiple single-shot images, generating an averaged image with significantly higher signal-to-noise ratio than obtained with unregistered averaging. Reflection high-energy electron diffraction (RHEED) was also demonstrated, showing that cold atom electron sources may be useful in resolving nanosecond dynamics of nanometre scale near-surface structures.

Compact ultracold electron source based on a grating magneto-optical trap

“…In the UCES high charge electron bunches are created by near threshold photo-ionisation of a cloud of laser-cooled and trapped atoms in a magneto optical trap (MOT) 22 . Previous work showed high quality diffraction patterns 23,24 with these bunches, demonstrating pulsed electron source temperatures as low [19][20][21] as a few-10 K. Additionally it was shown that it is possible to extract ultracold picosecond electron pulses 25 which can in principle be compressed to ∼ 100fs using well established RF compression techniques 26 .…”

Field ionization of Rydberg atoms for high-brightness electron and ion beams

“…Careful ionization of an atomic ensemble, either directly or via a field-assisted process, produces inherently cold electron bunches, giving an impressively small transverse energy spread [8,9]. Electron beams with energies of U = 1-10 keV [10,11] have been produced by ionizing atoms in a static electric field, with the finite size of the ionization volume giving rise to a * scholten@unimelb.edu.au longitudinal energy spread on the order of 0.01% of the beam energy ( U = 0.1-1 eV). One possible mechanism to achieve reduced energy spread is field ionization of highly excited Rydberg atoms [12].…”

Time-resolved brightness measurements by streaking

“…The next generation of CAES designs will be capable of significantly higher bunch charge, which will make single-shot measurements feasible, allowing for more precise measurements and permitting investigations of temporal bunch behavior in the femtosecond regime. By utilizing ultrafast ionization pathways in a CAES, ultrashort electron bunches can be generated [22,45] and the pepperpot-streaking system shown here could also prove useful in examining the efficacy of techniques to counter space charge expansion by observing the temporal behavior of space-charge driven emittance degradation [21]. This technique could serve as a powerful tool for the determination of time-resolved brightness for charged particle beams.…”