  Motivated by recent photoemission experiments on the surface of topological
insulators we compute the spectrum of driven topological surface excitations in
the presence of an external light source. We completely characterize the
spectral function of these non-equilibrium electron excitations for both linear
and circular polarizations of the incident light. We find that in the latter
case, the circularly polarized light gaps out the surface states, whereas
linear polarization gives rise to an anisotropic metal with multiple Dirac
cones. We compare the sizes of the gaps with recent pump-probe photoemission
measurements and find good agreement. We also identify theoretically several
new features in the time-dependent spectral function, such as shadow Dirac
cones.
