DOES FEMTOSECOND TIME-RESOLVED 2ND-HARMONIC GENERATION PROBE ELECTRONTEMPERATURES AT SURFACES

Femtosecond pump-probe second-harmonic generation (SHG) and transient linear reflectivity measurements were carried out on polycrystalline C u, Ag and Au in air to analyze whether the electron temperature affect s Fresnel factors or nonlinear susceptibilities, or both. Sensitivity to electron temperatures was attained by using photon energies near th e interband transition threshold. We find that the nonlinear susceptib ility carries the electron temperature dependence in case of Ag and Au , while for Cu the dependence is in the Fresnel factors. This contrast ing behavior emphasizes that SHG is not a priori sensitive to electron dynamics at surfaces or interfaces, notwithstanding its cause.