Study On Surface Plasmons Generated By Free Electron Excited Metal Micro-Nano Structures

The electromagnetic radiation sources obtained by traditional electronic and photonics methods often have great limitations,and it is difficult to meet the requirements of high frequency and high power at the same time.The terahertz frequency band is between the microwave and visible light frequency bands.It is the only remaining "virgin land" in the electromagnetic spectrum,and has the advantages of both electronics and photonics.This dissertation mainly starts from the characteristics of surface plasmons in metals,and analyzes their characteristics of generating electromagnetic radiation in the visible light band.This feature is expected to be extended to the terahertz band in subsequent studies.Firstly,the basic properties of surface plasmons are introduced,and then the properties of surface plasmons in metal structures are studied by numerical calculation and simulation analysis based on the basic electromagnetic field theory.Surface plasmons can be excited in metal structures,in which continuous metal structures are excited by surface plasmon polaritons(SPPs),and discontinuous metal structures are excited by localized surface plasmons(LSPs).Surface plasmon polaritons can be divided into symmetric and asymmetric modes,and their frequencies are related to metal material,thickness and free electron energy.When the thickness of the metal film increases gradually,the polaron frequencies of these two modes gradually approach and finally degenerate into one frequency.For structures that are confined in all three dimensions,such as gold nanoparticles,localized surface plasmons are excited,the frequency of which is determined by the metal structure and the electron beam energy.Subsequently,the physical model of the strong absorption of the ultrathin metal film was theoretically derived,and the LSP frequency tuned by its strip structure was simulated.Second,the use of surface plasmons coherence to enhance the study of Smith-Purcell radiation.Firstly,the Smith-Purcel radiation emitted from the free electron excited PEC grating is studied.The wavelength range of the negative harmonic is related to the grating period and the free electron energy.The radiation intensity is jointly determined by the electron beam energy,the grating depth and the grating gap width.When free electrons excite the gold grating,surface plasmons and Smith-Purcell radiation are simultaneously excited and can be tuned by adjusting the grating structural parameters and electron beam energy.At the same time,the excitation results of surface plasmons in different structures are distinguished by simulation method by setting up a control group.Finally,in order to obtain a better enhancement effect,the structural parameters of the gold grating are also simulated.Finally,surface plasmon polaritons in the Kretschmann structure were excited using a broadband xenon light source.Using a semi-cylindrical prism,experimental measurements verified that the Drude model for gold no longer holds true at higher electron beam energies.Then,using the high-energy electron beam generated by the SEM,an optical path system was designed and built inside the electron microscope,and the excitation experiment was performed on the gold grating to observe the spectral signal of the radiation field,and analyze the experimental measurement results.Finally,the radiation signal of the localized surface plasmons is obtained by the experimental measurement.