Pyramid-shaped plasmonic slit for optical transmission

Localized surface plasmons are highly confined modes at the subwavelength surfaces. The modes provide enhanced electric field intensity sites in close proximity to the surface which display potential applications in the form of optical-sensing devices. Intriguingly, at nanoscale, the modes can also increase the optical transmission through the aperture. In this work, we analyze the light transmission through a pyramid-shaped slit based on numerical simulations. We demonstrate the phenomenon by studying the behavior of Poynting vectors in the near surroundings of the slit. Furthermore, near and far transmitted optical intensities are calculated which show the supremacy of pyramid-shaped slit over the rectangular-shaped slit. The near and far field intensity through the pyramid slit is ∼2.25-times stronger than that of the rectangular slit. To see the influence of the shape of the slit on optical transmission, a reverse case, wherein pyramid-shaped slit is rotated by 180°, is also investigated. Based on our analysis, it is shown that enhancement of the output field emanates due to the excitation of the LSP modes while directionality of the field by a single slit depends on the shape of the slit. The study could be useful for the enhancement of fluorescent and Raman emissions from the molecules that are located eminently close to the slit.