The dynamics of charge transfer and electronic excitations are of fundamental importance in
many areas of surface physics. At metal surfaces electronic relaxation occurs on the
timescale of femtoseconds due to the strong resonant coupling with a continuum of substrate
excitations. Recent advances in ultrafast laser sources and the development of nonlinear
laser-based surface probes, in particular the technique of time-resolved photoemission, now
make it possible to investigate the electron dynamics at surfaces directly in the time domain …

An equal pulse correlation technique based on angle-resolved two-photon photoemission is
employed to investigate the lifetime of electronic excitations of an adsorbate on a single
crystal metal surface. Photoemission from an occupied surface state on Cu (111) by a non-
resonant two-photon process via the sp-band gap is used to characterize directly at the
surface the width and shape of 65 fs laser pulses at a photon energy of hv= 3.4 eV. The
2PPE correlation technique allows the establishment of an upper limit of τ< 20 fs for the …