  In laser-wakefield acceleration, an ultra-intense laser pulse is focused into
an underdense plasma in order to accelerate electrons to relativistic
velocities. In most cases, the pulses consist of multiple optical cycles and
the interaction is well described in the framework of the ponderomotive force
where only the envelope of the laser has to be considered. But when using
single-cycle pulses, the ponderomotive approximation breaks down, and the
actual waveform of the laser has to be taken into account. In this paper, we
use near-single cycle laser pulses to drive a laser-wakefield accelerator. We
observe variations of the electron beam pointing on the order of 10 mrad in the
polarisation direction, as well as 30% variations of the beam charge, locked to
the value of the controlled laser carrier-envelope phase, in both nitrogen and
helium plasma. Those findings are explained through particle-in-cell
simulations indicating that low-emittance, ultra-short electron bunches are
periodically injected off-axis by the transversally oscillating bubble
associated with the slipping carrier-envelope phase.
