OPTICAL DEPHASING IN CU(111) MEASURED BY INTERFEROMETRIC 2-PHOTON TIME-RESOLVED PHOTOEMISSION

The polarization dynamics induced by the optical excitation of the s,p -band derived occupied surface state on Cu(111) are studied by a new t echnique, interferometric two-photon time-resolved photoemission. The polarization decay due to phase breaking collisions of the charge carr iers on an similar to 20 fs time scale is modeled by the optical Bloch equations. The optical phase resolution also allows direct observatio n of nonlinear polarization oscillations at the harmonics of the excit ation frequency, which lead to the surface harmonic generation.