Optical excitation of acoustic surface plasmons in metallic nanoparticles

Acoustic surface plasmons are low energy collective excitations occurring at metallic surfaces. These excitations show a linear dispersion which can be described using realistic quantum-mechanical models. The response function of Ag(111) films is calculated and an effective dielectric function of the films is obtained. With use of this dielectric function the scattering of silver nanoparticles in the infrared range is calculated, with focus on the possibility of excitation of localized acoustic surface plasmons. Our calculations show that it is possible to excite optically localized acoustic surface plasmons in silver spheres, although the efficiency is very low.