Metal Nanoparticle Ensembles: Tunable Laser Pulses Distinguish Monomer from Dimer Vibrations

PABLO M JAIS; DANIEL B MURRAY; R. MERLIN; A. V. BRAGAS

Erice

Conferencia; INTERNATIONAL SCHOOL OF QUANTUM ELECTRONICS. Second Mediterranean International Workshop on Photoacoustic & Photothermal Phenomena; 2012

: Tunable optical pulses are used to excite selectively coherent mechanical oscillations in the 5-150 GHz range, assigned to vibrations of isolated spheres or pairs of contacting spheres, in an ensemble of gold nanoparticles. The amplitudes of the oscillations exhibit a strong enhancement when the laser central wavelength is tuned to resonate with the corresponding plasmon. Our approach distinguishes itself in that we are able to discriminate between modes of individual spheres and pairs of connecting spheres without recurring to single-particle detection. Because of the resonant selection in the excitation process, the widths of the acoustic modes are significantly smaller than broadening caused by the spread in radii in the ensemble.