Optical decoherence and quantum beats in Cs/Cu(111)

Electron dynamics induced by optical excitation from the occupied Shockley surface state to an unoccupied state localized on Cs atoms on Cu(111) is st udied by interferometric time-resolved two-photon photoemission. With near- resonant excitation, beat structures are observed in interferometric two-pu lse correlation measurements, where the two-photon photoemission intensity is measured as a function of pump-probe delay time. The quantum beats that originate from the frequency differences among initial-intermediate and int ermediate-final states, and the carrier frequency are reproduced qualitativ ely by a three-level optical Bloch equation model. (C) 1999 Elsevier Scienc e B.V. All rights reserved.