Near-Field Spectral Characterization of Asymmetric Coupling Two Nanorods Structures

The finite-difference time-domain method characterizes the near-field responses at different ends of the asymmetric nanorod structures. The results show that two modes exist in the long and short rods: low-frequency mode (LFM) and high-frequency mode (HFM). The field enhancement of the LFM at the gap end points is considerably higher than that at the outer end points. For HFM, the intensity at the gap end point of the long rod is stronger than that at the outer end point; however, the intensity at the two end points of the short rod is the same. The difference in the intensity response at different ends of two nanorods is attributed to the charge reservoir effect resulting from the different intrinsic frequencies of the nanorods. Furthermore, the oscillation frequencies of different end points are consistent at both ends of resonant nanorods and different at nonresonant nanorods. In addition, the oscillation frequency at the gap end point of the nonresonant nanorod is closer to that of the resonant frequency compared with the one at the outer point.