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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 technique, interferometric two-photon time-resolved photoemission. The polarization decay due to phase breaking collisions of the charge carriers on an ϳ20 fs time scale is modeled by the optical Bloch equations. The optical phase resolution also allows direct observation of nonlinear polarization oscillations at the harmonics of the excitation frequency, which lead to the surface harmonic generation. [S0031-9007(97)02319-3]

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The temperature and density dependence of spin quantum beats of electrons is measured by time-resolved photoluminescence spectroscopy and yields the electron Landé g factor in bulk GaAs, InP, and CdTe. In GaAs the g factor increases linearly from Ϫ0.44 at 4 K to Ϫ0.30 at 280 K; in InP the g factor is 1.20 at 4 K, exhibiting a very small temperature dependence up to 160 K, and in CdTe the g factor follows between Tϭ4 K and 240 K the empirical equation gϭϪ1.653ϩ4ϫ10 Ϫ4 Tϩ2.8ϫ10 Ϫ6 T 2 . In GaAs we demonstrate the suppression of spin quantum beats due to Fermi blocking in a degenerate electron gas and measure an increase of the GaAs g factor from Ϫ0.44 at densities below 1ϫ10 16 cm Ϫ3 to Ϫ0.33 at 10 17 cm Ϫ3 .