The Physical Characteristics Of The Smith Purcell Radiation Based On The High Q Microcavity

The resonant cavity can make the local electromagnetic field in a small mode volume and make it oscillate continuously,with the characteristics of high-quality factor Q and high energy density of the light field.The structures that form the cavity include Whispering Gallery Mode cavity,classic Fabry-Perot cavity,and photonic crystal microcavities.In this paper,the BICs of cavity structure is verified by the method of eigenmode analysis and topological charge calculation of various cavity structures,as well as the transmission spectrum,structural near-field analysis and multipole scattering calculation.The quasi-BIC frequency point of the structure is used to realize the Smith-Purcell radiation(SP radiation)with ultra-high radiation power in a specific direction.The research contents of this paper are as follows:Firstly,based on photonic crystals,the infinitely long structural bands,and their spectral characteristics,as well as the influence of structural parameters,lattice period and material properties on the bandgap and flat band in the bandgap of defective structures were analyzed.The bound states in the continuum realized in the light line of the triangular lattice photonic crystal slab were discussed and designed,and the correctness of the calculation method was comprehensively verified by eigenmode analysis and topological charge calculation and compared with the existing research results.Secondly,we proposed the all-dielectric Metasurface structures and the metal Metasurface structures,and the BIC of the structure is determined by the analysis of the structure eigenmode and the topological charge calculation.The quasi-BIC can be realized,by breaking the symmetry of the structure,and the high-quality factor,near-field mode analysis and multipole scattering power calculation extracted from the transmission spectrum determine the formation of resonance from broad spectrum and narrow spectrum resonance.The results are also numerically fitted by the Fano’formula and the coupled mode theory,and the fitting parameters not only explain the change of line shape in the transmission spectrum,but also reveal the transition mechanism between ideal BIC and quasi-BIC.And the last,based on the microcavity structure proposed and involved in this paper,SP radiation and high-energy radiation power corresponding to specific electron beam speeds are realized by using the property of the BICs and the enormous quality factor Q in the small module volume.For the photonic crystal structure,the adjustable range of SP radiation angle of 57°and the radiation power density of about 600 W/m~2are realized by using the characteristics of changing the period without changing the resonant frequency point,and the quasi-BIC characteristics realized by the cavity.For all-dielectric and metal Metasurface,specific directional radiation is realized in the terahertz band and8 GHz～9 GHz band,respectively,and a radiated power density of about 1600 W/m~2is also obtained.