Simulation of two-photon photoemission from the bulksp-bands of Ag(111)

Abstract

Theoretical and experimental studies on the two-photon photoemission excited by femtosecond laser pulses from the $sp$-band of Ag(111) in normal direction are reported. At low temperatures, the two-photon photoemission spectrum is found to consist mainly of nonresonant direct transitions from the lower to the upper $sp$-band across the $L$-projected band gap involving the upper $sp$-band as virtual intermediate states. This direct photoemission signal is calculated from the Ag band structure using optical Bloch equations and dipole moments derived from the nearly free electron approximation. For finite temperatures, a minor additional temperature-dependent, continuous contribution to the two-photon photoemission spectrum is experimentally determined. This background due to the secondary electrons is theoretically modeled combining the Debye model and Fermi Liquid Theory to account for electron relaxation effects during the two-photon photoemission process.