  Plasmas are beset with instabilities of all types, hydrodynamic,
magneto-hydrodynamic, and electromagnetic. These instabilities are complex,
occur over a large range of temporal and spatial scales, are most often
unmanageable, and have seriously challenged our efforts at applications, even
as they have shed light on the understanding of the physics of plasmas in the
laboratory and astrophysical environments. A major reason for our limited
success in their containment is the lack of direct experimental information on
their origins and evolution, both temporal and spatial. In plasmas produced by
high-intensity, short, and ultrashort pulse lasers, our knowledge of the
instability stems from the (secondary) signals they generate e.g. scattering of
electromagnetic waves in the form of Raman or Brillouin scattering. Rarely, if
ever, has a direct measurement been made of the instantaneous evolution of the
instabilities in plasmas. In this paper, we present direct measurements of the
femtosecond evolution of the electromagnetic beam-driven instability that
arises from the interaction of forward and return currents in an
ultrahigh-intensity laser-produced plasma on a solid target.
