Light radiation from surface plasmon polaritons in a structure of nanometal film on a subwavelength dielectric grating

A nanoscale light radiation source based on the diffraction radiation mechanism is proposed. In this mechanism, tunable and highly directional light emission from visible to ultraviolet frequency regime can be generated from surface plasmon polaritons (SPPs) excited by a moving electron beam above a nanometal film embedded on a subwavelength dielectric grating. The light emits in both the free-space and the dielectric substrate in specific directions. The radiation frequencies can be widely tuned by adjusting the beam energy or structure parameters. A remarkable enhancement (up to three orders of magnitude) of the radiation power density is found. The origin of the enhancement is the strong local field. Furthermore, an interesting physical phenomenon of radiation interference in the dielectric substrate is found. The physical origin of the interference is uncovered and discussed. With advances of miniature size, compatible on-chip integration, high power density, well directionality and wavelength tunability, our result has potential applications in electronic-photonic and nanophotonic systems as on-chip light sources, or in electron-emitter displays building into large-area array.