Enhanced optical forces between coupled resonant metal nanoparticles

We investigate numerically the optical forces between noble metal naraparticles sustaining localized surface plasmon resonances. Our results first point out enhanced binding optical forces compared with dielectric nanaparticles and nonresonant metallic nanoparticles. We also show that under suitable illumination conditions, short-range forces tend to make the nanoparticles cluster, leading to intense and localized hot spots in the interstices. This effect corroborates recent experimental observations of an enhanced Raman signal in trapped metal sphere ensembles. (c) 2007 Optical Society of America.