Recently great attention and interest have been paid to the enhanced Cherenkov light radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch in a structure of thin metal film with dielectric-medium loading. This paper proposes a modified structure with a dielectric film covered above the metal film of aforementioned structure, which can improve the radiation characteristics by its effective manipulation on the dispersion property of surface plasmon polaritons. The required exciting electron beam energy for generation of light radiation from visible to ultraviolet frequency regime is dramatically lowered. Furthermore, the radiation power density reaches several times that of the original one due to stronger confinement of surface plasmon polaritons on the metal film. The dependence of radiation characteristics including radiation frequency and power density on the permittivity and thickness of dielectric film are studied in detail. The lower exciting electron beam energy and higher radiation power density of the modified structure will facilitate the practical application of a coherent, tunable and compact integrated light radiation source.

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