Ultrafast acoustic phonon generation in gold

Abstract

We investigate the ultrafast generation of coherent longitudinal acoustic phonons in gold films with a femtosecond optical pump and probe technique. The strain pulses observed are much broader than expected from simple thermoelastic generation. This is explained by the supersonic diffusion of electrons over distances much larger than the optical absorption depth. The electron-phonon coupling constant can be estimated directly from the phonon pulse duration. Using a novel analytical approach, we present an extension of the model to include electron-electron interactions.