Plasmon-coupling-induced photon scattering torque

Abstract

Bio-compatible Au nanoparticles exhibit great advantages in the application of biomedical research, such as bio-sensing, medical diagnosis, and cancer therapy. Bio-molecules can even be manipulated by laser tweezers with the optically trapped Au nanoparticles as handles. In this paper, optical scattering torque arising from coupled Au nanoparticles driven by circularly polarized light is theoretically presented. The coupled plasmon resonance modes boost the angular momentum transfer from photons to Au nanoparticle dimers and trimers through light absorption and scattering. The scattering process does not bring any optical-heating side effect that always accompanies light absorption. The generated optical torques on the nanostructures highly depend on the plasmon coupling in the structures. Each scattered incident circularly polarized photon can transfer as large as 2 ℏ angular momentum to the nanostructures. The results suggest that coupled plasmonic nanoparticle oligomers are promising candidates to construct optically driven rotary nanomotors that can be applied in biomedical applications.