Abstract
Electron-electron and electron-phonon thermalization processes are investigated in gold films using a high-sensitivity multiple-wavelength femtosecond pump-probe technique. A nonequilibrium electron distribution is excited by free-carrier absorption of an infrared femtosecond pulse and its relaxation dynamics followed by measuring the transient reflectivity and transmissivity with a visible probe pulse. Measurements performed in a thin gold film in the very low perturbation limit (\ensuremath{\Delta}${\mathit{T}}_{\mathit{e}}$\ensuremath{\sim}20 K) yield evidence for the existence of a non-Fermi electron distribution with an electron thermalization time of \ensuremath{\sim}500 fs and an electron-lattice interaction time of 1 ps. The apparent thermalization dynamics of the electron gas is much faster in optically thick samples and is shown to be dominated by transport effects.
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