Three-dimensional nano-optical assembly of antenna structures with collective near-field coupling

Metallic nanostructures are used for various applications because of their characteristic optical responses that generate strong near-fields. We have theoretically clarified that the configuration of nanoparticles (NPs) and their optical properties can be controlled by optical manipulation. In this study, we greatly improved our previously reported simulation method, and this improvement enables investigation of the stable states of optically trapped NPs in a three-dimensional system. On the basis of this method, the assembly process of rod-shaped silver NPs is concisely clarified, where NPs of a specific shape are selectively assembled even in a mixture of NPs of different shapes. In particular, our simulation method clarifies how a light-induced force drives assembly processes, which is an important subject to consider for extending the degree of freedom of an optical manipulation. Furthermore, as reported in our previous studies, an assembled structure inherits the properties of light used for the optical trapping; e.g., rod-shaped silver NPs are radially connected to each other and assembled into a ring-shaped structure under the irradiation of a radially polarized vector beam with a ring-shaped intensity distribution. The assembled structure is an artificial light-harvesting antenna because it theoretically exhibits an enhancement of near-field and extinction in a broader wavelength range than that of the original NPs composing the antenna and also a response to the non-polarized light such as the sunlight. On the basis of an optically manipulated configuration of NPs and their optical properties, we discuss the selective optical assembly in a three-dimensional simulation.