Dynamics of photoexcited electrons in metals studied with time-resolved two-photon photoemission
E. Knoesel, A. Hotzel, T. Hertel, M. Wolf and G. Ertl
Femtosecond time-resolved two-photon photoemission (2PPE) is used to investigate the electron dynamics of Cu(111), Ag(110) and Ta(poly). The experimentally derived relaxation rates of photoexcited electrons scale with the available phase space for scattering with electrons below the Fermi level and are compared with predictions from Fermi liquid theory. A simulation employing rate equations to account for hot electron lifetimes, transport effects and the creation of secondary electrons demonstrates that the relaxation dynamics is strongly influenced by secondary electron cascades. With Ag(110) a pronounced temperature dependence of the photoemission yield is observed indicating the importance of electron-phonon scattering for momentum conservation in the 2PPE process.