Research On Ag Nanoparticle Film-Coupled Optical Nanoantenna

Having a good response between incident light and metal nanoparticles,which will achieve a strong enhancement of electric field in local field,can control the radiation of fluorescence molecules or quantum dots.This is the most popular researches in Nanophotonics.Owing to metal nanoparticle can couple the incident light into local field strongly,charges on the surface of metal nanoparticle are collected oscillating which can produce Localized Surface Plasmons(LSP)on the surface of nanoparticle.Based on the optical antenna which consists of rhombus nanoparticle or ellipse nanodisk,it can produce LSP from the energy of incident light to realize electric field enhancement on the surface of metal nanoparticle,moreover,it can also change the localized density of state of fluorescence molecules or quantum dots near the metal nanoparticle to enhance it's radiation properties.Thus the optical nanoantenna can be applied significantly in image of Surface Plasmonic Resonance(SPR),Surface Plasmonic Waveguide,BiologicalSensor and Spectrum Enhancement.In this thesis,we make a summary for introducing the progress of optical nanoantenna,theories of surface plasmon,local surface plasmon,spontaneous radiation and classical antenna.Based on these theories,we have designed rhombus nanoantenna that can enhance electric field strongly.Finally,we have analyzed charges distribution on the surface of metal nanoparticle under the different dipole resonance modes.In this article,our major works as follow:1.Based on the LSP of metal nanoparticle,charges collecting on the surface of nanoantenna's sharp tip,shaping the hot spot can produce strong electric field.We have designed rhombus nanoantenna at the first time by using FDTD solutions software to simulate it.Therefore we have achieved 250 times of electric field enhancement which is stronger than others.In addition,we have adjusted the sharp angle along the long axis of rhombus and analyzed the electric field distribution of each structure.Moreover,in order to achieve greater Purcell factor of electric dipole,we put the electric dipole near the sharp tip of rhombus nanoparticle.The radiation direction and Localized Density of State(LDOS)have also been achieved in this article.Finally,to explain the result of this rhombus nanoantenna,we regard the optical antenna as the classical microstrip antenna using transmission line mode theory to calculate radiation loss resistance.From this perspective,we can understand that rhombus nanoantenna has stronger electric field enhancement than that of cubic nanoantenna.2.With the change of incident light angle,there has excited different resonance modes on the metal nanoparticle.We have analyzed charges distribution on the surface of metal nanoparticle in the condition of different resonance modes by using FDTD solutions.It also indicates that charges trend to gather at the corner and edge of nanoparticle.3.A ellipse nanodisk film coupled nanoantenna has also been designed in this thesis.By changing the ratio of long axis and short axis,we have calculated each nanostructures' scattering cross section,then we have also analyzed the electric field distribution of dipole resonance mode and quadrupole resonance mode which were excited by resonance wavelength light.