  We propose a simple laser-driven electron acceleration scheme based on
tightly focused radially polarized laser pulses for the production of
femtosecond electron bunches with energies in the few-hundreds-of-keV range. In
this method, the electrons are accelerated forward in the focal volume by the
longitudinal electric field component of the laser pulse. Three-dimensional
test-particle and particle-in-cell simulations reveal the feasibility of
generating well-collimated electron bunches with an energy spread of 5% and a
temporal duration of the order of 1 fs. These results offer a route towards
unprecedented time resolution in ultrafast electron diffraction experiments.
