Far- and near-field optical properties of Al nanorod by discrete dipole approximation

We report a detailed theoretical investigation about the influence of the nanorod length and incident polarization on the far-field and near-field optical properties of Al nanorod using the discrete dipole approximation. The results show that Al nanorod has great tunability in the UV-Vis-NIR region and much stronger near-field intensity at UV and NIR wave-lengths. The band position of transverse mode (TM) for the nanorod has a little blueshifted as the length increases, while that of the longitudinal mode (LM) is linearly redshifted with the size. In addition, we investigate how the incident polarization affects the extinction position and efficiency of the TM and LM. Finally, the near-field distribution dependences of the nanorod length for the TM and the LM have been analyzed. It is shown that much enhanced near-field always occur in the lateral surface of the nanorod for TM and the tip of the nanorod for the LM, respectively. The maximum local field enhancement factor of the TM is found to be about two times higher than that of the LM, which is due to close the region of interband transitions at about lambda = 800 nm. These results would be of great potential application in localized surface plasmon resonance sensor and UV-plasmonic device.