Probing the optical near field of a nanolens

Summary form only given. Dielectric core-metal shell nanoparticles, known as metal nanoshells, have been shown to possess broadly tunable plasmon resonances whose frequency can be controlled by the relative thickness of the nanoparticle layers. Since the internal geometry controls the far field electromagnetic response, it follows that the local electromagnetic field at the nanoshell surface is also controllable by varying its geometry. We characterize this nanolens by measuring the local electromagnetic field at the nanoshell surface as a function of the nanoparticle's core and shell dimensions via the surface enhanced Raman scattering response from a monolayer of nonresonant adsorbate molecules bound to the nanoparticle surface.