  Plasma wakefield acceleration (PWFA) is a novel acceleration technique with
promising prospects for both particle colliders and light sources. However,
PWFA research has so far been limited to a few large-scale accelerator
facilities world-wide. Here, we present first results on plasma wakefield
generation using electron beams accelerated with a 100-TW-class Ti:Sa laser.
Due to their ultrashort duration and high charge density, the laser-accelerated
electron bunches are suitable to drive plasma waves at electron densities in
the order of $10^{19}$ cm$^{-3}$. We capture the beam-induced plasma dynamics
with femtosecond resolution using few-cycle optical probing and, in addition to
the plasma wave itself, we observe a distinctive transverse ion motion in its
trail. This previously unobserved phenomenon can be explained by the
ponderomotive force of the plasma wave acting on the ions, resulting in a
modulation of the plasma density over many picoseconds. Due to the scaling laws
of plasma wakefield generation, results obtained at high plasma density using
high-current laser-accelerated electron beams can be readily scaled to
low-density systems. Laser-driven PWFA experiments can thus act as miniature
models for their larger, conventional counterparts. Furthermore, our results
pave the way towards a novel generation of laser-driven PWFA, which can
potentially provide ultra-low emittance beams within a compact setup.
