Surface plasmon dynamics in arrays of subwavelength holes: the role of optical interband transitions

Using femtosecond optical spectroscopy, we study the ultrafast dynamics of the surface plasmon polaritons in gold arrays of subwavelength holes. A large time dependent spectral broadening and shift of the surface plasmon resonances are reported. The experimental results are modeled by the diffraction of a transverse electromagnetic field through the nanostructure, taking into account both the electron dynamics near the interband transitions and the Drude-like conductivity of the metal. Our analysis, using either a theoretical or an experimentally determined dielectric function of gold, suggests that the losses propagation in plasmonic devices is strongly influenced by intrinsic and extrinsic electron scattering mechanisms.