Coupling of plasmonic nanoparticles to their environments in the context of van der Waals–Casimir interactions

Abstract

We present experiments in which the interaction of a single gold nanoparticle with glass substrates or with another gold particle can be tuned by in-situ control of their separations using scanning probe technology. We record the plasmon resonances of the coupled systems as a function of the polarization of the incident field and the particle position. The distinct spectral changes of the scattered light from the particle pair are in good agreement with the outcome of finite difference time-domain (FDTD) calculations. We believe our experimental technique holds promise for the investigation of the van der Waals-Casimir type interactions between nanoscopic neutral bodies.

Metal nanoparticles in strongly confined beams: transmission, reflection and absorption

“…This suggests that such NPs could be used for fundamental experiments where quantum emitters are replaced by classical oscillating dipoles. These include studies on the van der Waals-Casimir interactions [20], and on the extinction properties of emitters [15]. In the latter case, one could investigate improved focusing systems, such as directional dipole waves [1] and perform simpler test experiments at room temperature with metal NPs instead of quantum emitters at cryogenic temperatures [15].…”

“…They exhibit distinct resonances even if their size is smaller than the incident wavelength because of the excitation of surface plasmon-polaritons [19]. In fact, we have recently performed experiments where gold NPs were used to investigate fundamental physical problems related to classical and quantum oscillators close to neutral bodies or interacting with each others [20,21].…”

An ultrasmall mode volume cantilever-based Fabry-Pérot microcavity

“…However, it should be born in mind that the exact knowledge of α for a given GNP is highly nontrivial. First, near-field coupling to the DBR surface modifies the GNP plasmon resonance and polarizability [38]. By using an analytical expression [39], we have estimated the polarizability of the GNP to increase by 1.1 times in the presence of the DBR upper layer alone.…”

Fluctuation-Induced Forces Between Atoms and Surfaces: The Casimir–Polder Interaction

“…The electric oscillator strength clearly dominates in the atom. Let us compare to a metallic nanosphere (gold is often used in experiments) and assume a Drude model (51) for the dielectric function. In terms of the volume V = 4πR 3 /3, we get an electric oscillator strength…”

“…Let us consider now the case where the atom is replaced by a nanosphere [34,51,52]. Indeed, if the sphere radius R is smaller than the penetration depth and the radiation wavelength, we can neglect higher order multipoles in the Mie expansion [53] and consider only the electric and magnetic dipole (the sphere is globally neutral).…”