Yoshihiko Mizumoto

Plasmon-Based Optical Trapping of Polymer Nano-Spheres as Explored by Confocal Fluorescence Microspectroscopy: A Possible Mechanism of a Resonant Excitation Effect

In optical trapping using photon force much enhanced by localized surface plasmon (LSP) in solution, we found that a resonant excitation effect can further enhance photon force. In this LSP-based optical trapping under a resonant excitation condition, an incident laser beam excites both LSP and electronic resonant transition of a target object simultaneously. Fluorescence microspectroscopy clearly showed that nanospheres under the resonant condition were much more efficiently trapped as compared to that under a non-resonant condition. The resonant LSP-based trapping mechanism was further reinforced by theoretical calculations taking the resonant excitation effect into account. Such resonant LSP-based trapping methodology will provide a novel approach for efficient trapping of small molecules.

Theory for self-consistent interplay between light and nanomaterials strongly modified by metallic nanostructures

The design of the interplay between light and nanomaterials by the effect of localized-surface-plasmon resonance in metallic nanostructures is a fascinating subject, and recently, a lot of research has been carried out from both fundamental and applicational points of view. In this paper, we demonstrate the theories for describing the self-consistent interplay between the electronic states in the nanomaterials, the localized surface plasmons in the metallic nanostructures, and the light field, which provides insight into how the photoexcitation processes are modified through microscopic energy exchanges. As examples of such demonstrations, we show two cases, i.e., the interaction between a single metallic nanosphere and a quantum dot, and that between metallic nanostructures forming a nanogap and dimer molecules, where a peculiar dependence of photoexcitation processes on the distance between the metallic nanostructure and the absorbers arises depending on the respective characteristics of their interplay.

Theory of resonant radiation force exerted on single organic molecules near metallic nanogap

By means of the extended discrete dipole approximation into which the microscopic nonlocal response is incorporated, we theoretically demonstrate the radiation force and torque exerted on single molecules near the metallic nanogap. In this theory, we consider the spatial interplay between the light electric field localized within a nanometer-sized region and molecular wavefunctions. The results show a strong enhancement of exerted force due to the plasmonic and electronic double resonances, and also show the possibility of selective control of molecular alignment and orientation near the nanogap by the resonance laser manipulation.