The coherent, power enhanced and mode selected light radiation from the coupling of surface plasmon polaritons (SPPs) and waveguide modes is presented here. The results of theoretical analysis show that this coupling occurs in the structure of a thin metal film with finite thickness dielectric medium loading excited by free electrons at certain beam energies, referred to as the coupling points. The research of particle-in-cell simulation is also carried out, and results agree well that of theoretical analyses. Because of the coupling, the power intensity of the coherent radiation is extremely enhanced up to 32 times compared with that transformed from SPPs by Cherenkov radiation directly in the infinite medium. And even at the non-coupling points, there is also a 5 times enhancement of the radiation power. The results also show that the main mode of the loading medium is changed from the zero order waveguide mode to the mode whose operating frequency is near to that of asymmetric SPPs mode. Accordingly, the results presented here is of great significance of developing miniature, integratable, high-power-density light radiation sources from visible light to ultra-violet rays at room temperature.

Cherenkov radiations; Coherent radiation; Dielectric medium; High power density; Operating frequency; Particle-in-cell simulations; Surface plasmon polaritons; Waveguide coupling

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