Study On The Resonance Radiation Characteristics Of Silver Nano-trimers And Tetramers

Surface plasmons(SPs)is a kind of electromagnetic wave propagates along the metallic surface caused by the interaction between the optical field and the metal nano-structure.Surface plasmons show many unique optical properties,such as selective absorption,scattering,amplification,regulation and so on.Therefore,it has wide application value in data storage,biomedicine,waveguide,surface enhancement spectroscopy and negative refraction materials.In recent years,with the continuous maturation of nanometer material processing technology,a large number of studies have been carried out to reveal the optical properties of noble metal nanoparticles and nano-composite structures based on theory and experiment.It is found that changing the physical parameters in the structural system can adjust the coupling between the surface plasmons of the nanostructures,and then control the optical field.Based on the finite element method,this paper mainly studies the optical properties of two nano-structure systems.1.The resonant properties of the nano-composite structure which composed by a silver split nano-ring and two silver plates:The nano-trimer structure we studied consists of a silver split nano-ring and two silver nano-plates,that the two silver nano-plates are placed relative to each other and clinging to the split nano-ring.This structure is similar to a L-C circuit,the two silver nano-plates are equivalent to a capacitor,and the silver split nano-ring is similar to an inductive coil.Under the excitation of the optical field,by adjusting the structure size of the nano-plate can control the position,line width and intensity of resonant absorption peaks,which will be conducive to the application of surface plasmons in Surface enhancement Raman spectroscopy.The electric field enhancement at the gap of two silver nano-plates is related to the capacitance of the structure,by changing the capacitance of the structure can control the electric field,this will facilitate its application in the development of nano-level optical devices and optical nanocircuits.2.Fano resonances and linewidth compression in the Silver nanorod quadrumer:With the finite element method(FEM),we investigate the Fano resonances(FRs)and linewidth compression in a Silver nanorod quadrumer(SNQM)system formed from four silver nanorods.The SNQM is made up of two dimers,one composed by two identical and parallel silver nanorods that can be regarded as a Resonant cavity(RC),the other is inserted in the RC composed by two same silver nanorods oriented in the same direction which can be taken as a Dipole antenna(DA).The results show that the distinct FRs are observed in the transmission spectra of the SNQM,which derives from the interference between the super-radiant mode and the sub-radiant mode that caused by the interaction of the surface plasmons of the RC and DA.FRs can be tuned in both resonance wavelength and modulation depth by adjusting the structure parameters.Meanwhile,under the appropriate structure parameters,the narrow linewidth radiation of the DA can be enhanced in the RC.The results are crucial for many applications in the fields of biological sensing and Plasmon-induced transparency.