Plasmon resonance-enhanced photocathode by light trapping in periodic concentric circular nanocavities on gold surface

In this paper, we report the design and characterization of a new surface plasmon polariton (SPP) nanocavity on the surface of gold film to enhance the efficiency of metallic photocathodes. The plasmonic surface increases absorption over normal metals, and due to the localization of fields, this results in complete elimination of reflection from the metal surface. Here, a periodic array of concentric circular nanocavities on the gold surface was designed to exhibit multiband plasmonic resonances at 600 nm, 710 nm and 800 nm. We theoretically report on the enhancement of relative quantum efficiency from gold cathode up to 70 times compared to a flat surface, by use of nanostructured plasmonic surfaces to trap, localize, and enhance optical fields. The proposed structure have a number of useful practical features such as broadband or multiband absorption and broad angular bandwidth. The symmetry in the proposed structure eliminates any polarization dependence within the structure.