  Vortex-carrying matter waves, such as chiral electron beams, are of
significant interest in both applied and fundamental science. Continuous wave
electron vortex beams are commonly prepared via passive phase masks imprinting
a transverse phase modulation on the electron's wave function. Here, we show
that femtosecond chiral plasmonic near fields enable the generation and dynamic
control on the ultrafast timescale of an electron vortex beam. The vortex
structure of the resulting electron wavepacket is probed in both real and
reciprocal space using ultrafast transmission electron microscopy. This method
offers a high degree of scalability to small length scales and a highly
efficient manipulation of the electron vorticity with attosecond precision.
Besides the direct implications in the investigation of nanoscale ultrafast
processes in which chirality plays a major role, we further discuss the
perspectives of using this technique to shape the wave function of charged
composite particles, such as protons, and how it can be used to probe their
internal structure.
