  Simultaneous spatio-temporal confinement of energetic electron pulses to
femtosecond and nanometer scales is a topic of great interest in the scientific
community, given the potential impact of such development on a wide spectrum of
scientific and industrial applications. For example, in ultrafast electron
scattering, nanoscale probes would enable accurate maps of structural dynamics
in materials with nanoscale heterogeneity, thereby understanding the role of
boundaries and defects on macroscopic properties. On the other hand, advances
in this field are mostly limited by the electron source brightness and size. We
present the design, fabrication, and optical characterization of bullseye
plasmonic lenses for next-generation ultrafast electron sources. Using
electromagnetic simulations, we examine how the interplay between light-plasmon
coupling, plasmon propagation, dispersion, and resonance governs the properties
of the photoemitted electron pulse. We also illustrate how the pulse duration
and strength can be tuned by geometric design, and predict sub-10 fs pulses
with nanoscale diameter can be achieved. We then fabricated lenses in gold
films and characterized their plasmonic properties with cathodoluminescence
spectromicroscopy, demonstrating suitable plasmonic behavior for ultrafast,
nanoscale photoemission.
