Metallic nanoparticles (NP) draw intense scientific interest due to their unique physical properties, which differ from those of bulk and atomic species. Nowadays, the aim of this research area is focused, for example, in the nonlinear (NL) optical properties of NP, the dynamics of confined electrons and the possibility of photonic applications. In this work the transient response of non-spherical nanoparticles are studied. Two differently prepared colloids are examined: one sample has a broad distribution of sizes and shapes of silver nanoparticles, while the second sample, which is processed by laser ablation, presents a more uniform size and shape distribution (greater fraction of spherical particles). The experiments are performed with a Ti:sapphire femtosecond laser using a two-color, polarization-resolved, pump-probe setup. The pump pulse at ≈ 800 nm excites intraband transitions, heating the electronic distribution, while the probe pulse is scanned around the peak of the Surface Plasmon Ressoance (SPR): ≈ 400 nm. It is observed that for the pristine colloid (non-spherical particles) the signal amplitudes of the probe polarizations parallel and perpendicular to the pump polarization present different behaviors as a function of the probe photon energy. The same effect is not observed for the laser ablated samples, which are isotropic. The temporal response of the samples is also different, with the laser ablated samples presenting faster electronic cooling rates. A model describing the induced dichroism that takes into account the shape of the colloid particles is presented. The effects of the size distribution are also discussed.

Date Published: 15 February 2006
PDF: 8 pages
Proc. SPIE 6118, Ultrafast Phenomena in Semiconductors and Nanostructure Materials X, 61180S (15 February 2006);

Published in SPIE Proceedings Vol. 6118:
Ultrafast Phenomena in Semiconductors and Nanostructure Materials X
Kong-Thon Tsen; Jin-Joo Song; Hongxing Jiang, Editor(s)