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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.