Investigation of surface plasmons in Kretschmann structure loaded with a silver nano-cube

A composite structure based on a Kretschmann structure loaded with silver nano-cube is proposed. A 442-nm laser was used to excite surface plasmons in the composite structure, and the electric field enhancement was numerically simulated using the finite element method. The excitation angles of surface plasmons under conditions of different thicknesses of a PMMA film were obtained by studying the reflection spectrum of the Kretschmann structure. By examining the extinction spectra of silver nano-cubes of different sizes, its optimal size was selected, which is 70 nm. The electric field enhancement factors of the composite structure and the composite PMMA-spaced silver nano-cube and silver film structure were compared in detail. The results show that the coupling of localized surface plasmons and propagating surface plasmons produced by the proposed composite structure mean that its electric field enhancement factor is significantly greater. Moreover, the electric field enhancement factor can be further improved by adding another laser to irradiate the composite structure symmetrically. The high electric field enhancement generated by the composite structure indicates that it has considerable application prospects in surface-enhanced Raman scattering.