Ultrafast electron dynamics at Cu(111): Response of an electron gas to optical excitation

Time-resolved two-photon photoemission is used to directly investigate the electron dynamics at a Cu(111) surface with 60 fs laser pulses. We find that the time evolution of the photoexcited electron population in the first image state can be described only by solving the optical Bloch equations to properly account for coherence in the excitation process. Our experiments also provide evidence that the dynamics of photoexcited bulk electrons is strongly influenced by hot electron cascades and that the initial relaxation rates are in agreement with Fermi liquid theory.