Dresden 2009 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 11: Photonic Dielectrics II

DF 11.2: Talk

Wednesday, March 25, 2009, 15:10–15:30, WIL A317

Ultrafast shape transformation dynamics of silver nanoparticles studied by femtosecond pulse-pair irradiation — •Akin Unal, Andrei Stalmashonak, Gerhard Seifert, and Heinrich Graener — Institut für Physik, Fachgruppe Optik, Martin-Luther-Universität, Hoher Weg 8, 06120 Halle, Germany

Spherical silver nanoparticles embedded in glass were irradiated by pairs of time-delayed laser pulses with equal intensities resulting in delay-dependent nanoparticle shape transformations. The corresponding permanent changes of the surface plasmon extinction bands are analyzed as a function of time delay and relative polarization of the pulse pairs. We find that the strongest nanoparticle shape changes, i.e. the highest aspect ratios, are achieved when the delay between pulse pairs is less than 3 ps. After 10 ps the aspect ratio is strongly reduced in the case of pulse pairs having identical polarization and vanishes using pulse pairs with orthogonal polarization. Estimations of the time dependence of "pulse-enhanced" (directed) and thermal (isotropic) electron emissions obtained from an extended two-temperature model indicate a decay of the relative contribution of directed electron emission on the same time scale of a few picoseconds. Our results strongly suggest that the electron and following ion emission from the nanoparticles are finished within less than 20 ps, and the directional memory is favorably defined by directed emission of hot electrons interacting with the laser field.