  We investigate the ultrafast response of the bismuth (111) surface by means
of time resolved photoemission spectroscopy. The direct visualization of the
electronic structure allows us to gain insights on electron-electron and
electron-phonon interaction. Concerning electron-electron interaction, it is
found that electron thermalization is fluence dependent and can take as much as
several hundreds of femtoseconds at low fluences. This behavior is in
qualitative agreement with Landau's theory of Fermi liquids but the data show
deviations from the behavior of a common 3D degenerate electron gas. Concerning
electron-phonon interaction, our data allows us to directly observe the
coupling of individual Bloch state to the coherent $A_{1g}$ mode. It is found
that surface states are much less coupled to this mode when compared to bulk
states. This is confirmed by \textit{ab initio} calculations of surface and
bulk bismuth.
