  We present measurements of high-order harmonics and relativistic electrons
emitted into the vacuum from a plasma mirror driven by temporally-shaped
ultra-intense laser waveforms, produced by collinearly combining the main laser
field with its second harmonic. We experimentally show how these observables
are influenced by the phase delay between these two frequencies at the
attosecond timescale, and relate these observations to the underlying physics
through an advanced analysis of 1D/2D Particle-In-Cell simulations. These
results demonstrate that sub-cycle shaping of the driving laser field provides
fine control on the properties of the relativistic electron bunches responsible
for harmonic and particle emission from plasma mirrors.
