Wavelength-Dependent Optical Chiralities of Symmetric and Asymmetric 2-Shaped Au Nanorod Structures at Nanoscales

Two-shaped Au nanorod structures are used to create the optical chiralities at the surface plasmon resonances (SPRs) from visible to near-infrared wavelength range, which is theoretically explored by using the 3D finite difference time-domain method. To understand the effects of the middle horizontal Au nanorod on the optical energy coupling between the upper inverted L-shaped Au nanorods and the bottom regular L-shaped Au nanorods, the near-field distributions of the asymmetric and symmetric 2-shaped Au nanorod structures are discussed. The simulation results show that the three horizontal Au nanorods can effectively harvest the x-directed electric field of incident lightwaves and generate the z-directed electric field near the corners of Au nanorods and thereby result in the local optical chiralities at the three SPRs. In addition, the optical energy coupling from the horizontal Au nanorods to the vertical Au nanorods can contribute to the total optical chirality. The understanding of local and total optical chiralities of Au planar nanostructures at nanoscales helps us find the best way to optimize the metallic chiral nanostructures.