Research Of Multiple Fano Resonances Effect In Noble Metal Nanoparticle Cluster

The localized surface plasmon resonance of metal nanoparticle can exhibitunique electromagnetic enhancement and extinction effect. The energy ofincident light can be highly localized on the metal surface. Taking advantage ofthis localized feature can be break though the diffraction limit of light, whichhas received more and more attention from researchers. Two or morenanoparticles are placed close constituting complex nanostructures. Theplasmon of nanoparticles can couple by near-field interactions and result in aseries of plasmonic hybridized mode. When the placement of nanoparticles wasdesigned reasonable and the couple of near-field interactions is controlledproperly. The fano resonance interference effect can show in the complexnanostructure. For the fano resonance in the surface plasmon system, not onlythe radiation damping of complex nanostructure can be effectively reduced, butalso the energy of the incident light can be confined better in the complexnanostructure. The fano resonance can make the spectrum more fine andproduce stronger electromagnetic field enhancement, which can improve thesensing performance of symtem and nonlinear effects. Compared with the singlefano resonance, multiple fano resonances can modify spectrum at severalpositions, which can achieve the spectral lines controllable and adjust themultiple fano resonance peaks with it matching. The electromagnetic field canbe enhanced at multiple wavelengths and the enhancement factor ofSurface-enhanced Raman spectroscopy can be improve greatly. When the multiple fano resonances lines match with different molecular vibrationspectrum, it can achieve efficiently different molecules detecting. As the result,the fano resonance in the complex nanostructure are useful for biosensing,optical switching and surface-enhanced raman scattering.This paper is based on the properties of localized surface plasmonresonance and finite different time domain method is used to investigate themultiple fano resonances phenomena in several complex nanostructures. Themain work includes:(1) We study the fano resonance phenomenon in nanoring quadrumer andoctamer, analysis the near-field distribution at corresponding spectral positionsand discuss the forming reasons of fano resonance. The spectra position andmodulation depth of Fano resonance can be tuned by adjusting the angle andseparation of the nanorings. Because the energy gap between the dipole andquadrupole of split nanoring is small, we simulate the optical properties of thequadrumer and octamer comprising split nanorings. The calculation results showthat compared to nanoring quadrumer and octamer, the quadrumer and octamercomprising split nanorings can produce more fano resonances. Adjusting theangle and separation of the split nanorings, there are larger tunablity of thespectra position and modulation depth for each fano resonance.(2) The spectral characteristics and near-field distribution of L shapednanorod can be controlled by simply changing the incident polarization. Usingthis feature, we study the optical properties of two kinds of dimers composed ofL shaped nanorod with different incident polarization. And then constructingtwo complex nanostructure are gold nanorod complexes and L shape nanorodquadrumer. The results show that double fano resonances can appear in the goldnanorod complexes. The fano resonance can be tuned by changing the length ofnanorod. In addition, The complex metallic nanostructure can be divided intotwoseparate parts of L-shaped nanorods dimer and common nanorods dimer. wealter the length of nanorods in L-shaped nanorods dimer and common nanorods dimer respectively and compare the variation of their resonance positions, whichcan be considered for a full understanding of the over spectral lineshapevarying.For the L-shaped nanorods quadrumer, because of nanostructurerotationanl symmetry, the far-field optical properties of quadrumer isindependent with polarization. When the nanostucture symmetry of theL-shaped nanorods quadrumer is broken and the polarization change, three fanoresonances can be observed in the quadrumer.