Study on coupling of optical linear and angular momentum to nano-optical system

Abstract

Light carries linear and angular momentum. Although the momentum of light is a widely accepted concept, even the exact definition of light momentum still has some debates, especially in nanoscale. This dissertation studied the coupling of linear and angular momentum of light to a nano-optical system. The distribution of light scattering by a single subwavelength metal nanoantenna is experimentally measured and analyzed via the conservation of linear momentum of the light. We also schematically suggest a simple quantum well system to verify the role of the orbital angular momentum of light on transition selection rule by quantitative comparison of exciton absorption peaks while the angular momentum is quenched in semiconductor. We demonstrated direct observation of optical spin on nano plasmonic structure for the first time. In surface plasmon field distribution excited on zigzag metal nanostructure, we found the over the diffraction limit spatial separation of spin angular momentum density of light. We experimentally verified the physical validity of spin angular momentum density of confined surface plasmon field by measuring spatial pattern of circular polarization resolved photoluminescence distribution of the transition metal dichalcogenide (TMDC) employed in zigzag structure. The valley selective photoluminescence enables the TMDC medium to act as an effective probe of the spin angular momentum of light.