Determination of electron and phonon temperatures in gold thin film irradiated with an ultrashort laser pulse

We measured transient reflectivity of single-crystalline and polycrystalline gold thin films in the wavelength region of 450-700 nm pumped by a 400 nm femtosecond pulse. The observed reflectivity changes were reproduced well by a reflectivity model that we developed based on the joint-density-of-states calculated from the band structure of gold and the Drude model. By a combination use of the reflectivity model and the two-temperature model, we evaluated the temporal evolution of the electron and phonon temperatures from the observed reflectivity changes. Based on the resultant electron and phonon temperatures, we derived the electron-phonon coupling factors, which were consistent with the literature values, in the wide range of the absorbed energy density.