The Study On The Designing And Optimizing Metallic Nanoantennas To Enhance The Interaction Between Light And Matter

In recent years,the use of metal micro nanostructure plasmon mode coupled with fluorescent molecules or quantum dots and other luminescent materials has attracted extensive attention,which has important application prospects in biosensor,optical communication and integrated photonics.The production of luminescence usually includes two processes: excitation and emission.Due to the large local electric field enhancement on the surface of the metal micro nano structure when excited in the plasmon mode,when the luminescent body is in the "hot spot" position of these electric fields,the excitation process can be enhanced accordingly.However,when the luminescent body is too close to the metal micro nano structure,the excited electrons in the luminescent body can also be coupled with the high-order plasmon mode in the metal micro nano structure by non radiative transition,and the final energy is converted to ohmic loss,so as to reduce the efficiency of the fluorescence emission process,and even fluorescence quenching occurs.Therefore,in order to maximize the intensity of fluorescence radiation,it is necessary to balance the two effects of excitation enhancement and fluorescence quenching.Based on this,we study the influence of metal / medium interface on the excitation and emission of fluorescent molecules on the metal surface by coating a layer of dielectric film on the surface of the metal micro nano structure.The research content of this paper mainly includes the following two aspects:Firstly,we study the excitation and radiation process of the fluorescent molecules on the metal surface by theoretical and simulation calculation.It is found that the introduction of a dielectric film outside the gold particles can enhance the local electric field at the metal / dielectric interface,thus improving the quantum yield of the fluorescent molecules.Compared with the uncoated gold particle system,the core-shell structure system of metal / medium was formed by coating aluminum oxide dielectric film on the outside of the gold particle soaked with fluorescent molecules.We observed more than 20 times fluorescence enhancement in the experiment.At the same time,we find that the fluorescence lifetime of the molecule will be shortened in the metal / dielectric core-shell structure system,which is consistent with the theoretical simulation results.Secondly,we theoretically study the effects of dipole and higher-order plasmon modes supported by gold particles on the process of molecular fluorescence radiation.We found that with the decrease of the distance between the fluorescent molecule and the gold particle,the coupling between the high-order plasmon pseudo mode and the molecule will gradually enter the strong coupling range from the weak coupling range,and when the RF ratio of the fluorescence produced by the coupling between the dipole mode and the high-order pseudo mode and the molecule respectively matches,the maximum value of the fluorescence radiation intensity can be obtained.In the metal / dielectric core-shell structure system,we use the method that changing the thickness of the dielectric film can change the effective refractive index outside the gold particles,so as to effectively regulate the coupling strength of the dipole mode and the high-order pseudo mode interacting with the molecules respectively.We observe the phenomenon of fluorescence enhancement and cleavage,and preliminarily verify our theoretical analysis.