Squeezing the Optical Near-Field Zone by Plasmon Coupling of Metallic Nanoparticles

The study of electromagnetic eigenmodes of small metal particles is motivated by fundamental research and by possible applications of the optical properties of such particles. Most experimental works involve a large number of small metal particles embedded inside a dielectric material or deposited on a surface. The particles were studied as disordered or ordered arrays [1,2]. In both cases, their optical properties were affected by statistical and /or collective effects. The shape and size inhomogeneities of a large array of small metal particles lead to a statistical averaging of the optical properties. Collective effects due to the multiple scattering of light between the particles become significant when the distance between the particles is reduced to the order of magnitude of the incident wavelength. A recent experiment [3] determined the homogeneous linewidth of the plasmon resonance of metallic nanoparticles. In order to circumvent the inherent broadening associated to the large number of particles, a scanning near-field optical microscope (SNOM) was operated as a subwavelength local antenna to excite single nanoparticles in the near-field zone. The detection of the transmitted