FEMTOSECOND TIME-RESOLVED REFLECTION 2ND-HARMONIC GENERATION ON POLYCRYSTALLINE COPPER

Optical Second-Harmonic Generation (SHG) in reflection from a polycrystalline copper surface in air was studied using femtosecond time-resolved pump and probe measurements at lambda = 625 nm. The observed time dependence of second-harmonic yield from the probe beam demonstrates, that SHG is a very sensitive technique for measuring transient electron temperatures of metals even when these are covered by an oxide layer. For polycrystalline copper, an electron-phonon energy transfer time of 2 ps was observed, corresponding to a coupling constant of 3.75 x 10(17) W/m(3) K at average lattice temperatures of about 500 K. The analysis of experimental data indicates that the time dependence of SHG is governed by the linear dielectric function epsilon which, in turn, is affected by the electron temperature. There is no evidence for a temperature dependence of the nonlinear susceptibility chi((2)).