Study On Coupling And Hybrid Effects Of The Surface Plasmon For Metal Nanostructure

Metallic nanoparticles (NPs) have recently gained wide research interest because of the excitation of collective oscillation of conduction electrons called localized surface plasmon resonance (LSPR) within metal NPS in the visible and near-infrared region. The frequency and intensity of LSPR are highly dependent on the size, shape, morphology of the NPs and the surrounding dielectric medium. There are many different resonant modes of LSPR on nanostructures. The high-order plasmon modes would be induced when the size of the NPs increases. For complex nanostructures, the hybridization of the plasmonic modes can give rise to dark subradiant modes which has low radiative damping. In nanoparticle arrays, the LSPR of nanoparticles could couple to the optical diffraction arising from the dipolar scattering of the individual particle, leading to a very narrow plasmon line shapes and exceptionally large electromagnetic enhancements. These novel characters make the metallic NPs promising materials that could be extensively used in many photonic applications, such as ultrafast information processes, all-optical modulations, plasmonic metamaterials and biosensors.In this paper, we investigated the optical response of Au/Ag alloyed hollow nanoshells and other nanostructures.(1) We numerically investigate the resonant spectral features of the two-dimensional stacked double-disk array. Narrow plasmon line shapes are observed on resonance spectra which are similar to the case of single-disk array. The electric field shows that the narrow plasmon modes are produced by the dark plasmon mode coupling to the diffraction which may be due to the retardation effect. The narrow mode and the dark mode overlap on resonance spectra, resulting in a Fano-like spectrum. The intensities of the electric fields for these narrow modes arising from the dark mode coupling are much stronger than that of the bright modes.(2) We present a combination of experiment and theoretical simulation to investigate optical response of Au/Ag alloyed hollow nanoshells. The results show that two distinct plasmon resonances corresponding to the dipolar and quadrupolar modes appear in the extinction spectra of nanoshells. As the thickness of the shell decreases, the multiple modes consistently red-shift and the resonant intensity increases. The results are validated by the calculated electric field distribution of nanoshells.(3) We investigated enhanced-transmission induced by plasmon transfer from the bright mode to the dark modes. Furthermore, we demonstrated interferences between dark plasmons excited by the near-field bright plasmons and directly excited by slantwise incident light, which leads to selective storage of excited energy in one of the two dark plasmon cells in the resonators by adjusting the phase between signal and control sources. This could find the applications in all-optical modulations.(4) The localized surface plasmon (LSP) resonances properties of periodic arrays of nanoholes in thin gold films are investigated by using the method of discrete dipole approximation (DDA). The surface plasmon polaritons (SPPs) play important roles in amplification or suppression of the LSP resonances in the film. The intensity of the LSP resonances can be controlled through changing the edge-to-edge separation distances between nanoholes, the number and the diameter of the nanoholes.