Real-time optical mapping of the dynamics of nonthermal electrons in thin gold films

We investigate the nonlinear optical response of thin gold films with an unprecedented combination of high temporal resolution (similar to 15 fs) and broad spectral coverage. We quantitatively model the data without free parameters using an extended version of the two-temperature model. Our combined experimental and theoretical approach allows tracking the evolution from a purely nonthermal electron distribution towards a fully thermalized one. These results pose the basis for better understanding of light-matter interaction in metals on the ultrafast time scale.