FEMTOSECOND INVESTIGATION OF ELECTRON THERMALIZATION IN GOLD

Electron-electron and electron-phonon thermalization processes are inv estigated in gold films using a high-sensitivity multiple-wavelength f emtosecond pump-probe technique. A nonequilibrium electron distributio n is excited by free-carrier absorption of an infrared femtosecond pul se and its relaxation dynamics followed by measuring the transient ref lectivity and transmissivity with a visible probe pulse. Measurements performed in a thin gold film in the very low perturbation limit (DELT AT(e) approximately 20 K) yield evidence for the existence of a non-Fe rmi electron distribution with an electron thermalization time of appr oximately 500 fs and an electron-lattice interaction time of 1 ps. The apparent thermalization dynamics of the electron gas is much faster i n optically thick samples and is shown to be dominated by transport ef fects.