Femtosecond studies of the carrier phase and energy relaxation in metals

Summary form only given. Recent interferometric time-resolved two-photon photoemission (ITR-2PP) studies demonstrate that it is possible to create electron-hole pair excitations involving the carriers at the Fermi level, the top of the valance bands, and intrinsic and adsorbate induced surface states, where the phase relaxation can be significantly slower than the pulse-width of currently available ultrafast lasers. The ITR-2PP technique combines the merits of photoemission and ultrafast laser spectroscopies. which makes it possible to record the dynamics of specific excitations in metals. The energy and momentum analysis of electrons that undergo photoemission following pump and probe laser induced two-photon absorption provides the information on the carrier phase and energy relaxation at specified points in the Brillouin zone. ITR-2PP studies reveal various factors that determine the carrier phase and energy relaxation rates in metals such as the strength of electron-electron and electron-phonon interactions, and the spatial overlap of wavefunctions. Recent results on clean and alkali-atom covered low index surfaces of copper under ultrahigh vacuum conditions are reviewed.