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

Optical Second-Harmonic Generation (SHG) in reflection from a polycrys talline copper surface in air was studied using femtosecond time-resol ved 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 electro n 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 1 0(17) W/m(3) K at average lattice temperatures of about 500 K. The ana lysis of experimental data indicates that the time dependence of SHG i s governed by the linear dielectric function epsilon which, in turn, i s affected by the electron temperature. There is no evidence for a tem perature dependence of the nonlinear susceptibility chi((2)).