Excitation of Surface Plasmon Polaritons via Composite Structured Light

Abstract We propose a scheme for the excitation of surface plasmon polaritons (SPPs) at a metal-dielectric interface utilizing composite structured light. The proposed system is based on a three-layer structure, consisting of an upper transparent medium, a central metallic thin film, and a lower dielectric layer incorporating a four-level atomic system with an N-type configuration. We employ a weak probe field and two coupling fields, with the second coupling field being a composite vortex beam formed by the superposition of two Laguerre-Gaussian (LG) beams. We analyze the permittivity of the dielectric medium to verify the conditions for SPP excitation and observe SPP excitation at two different probe field detunings. We determine the optimal thickness of the metallic layer and the corresponding azimuthal angles required for efficient SPP excitation. We also examine the impact of the composite vortex beam on the permittivity and observe an 2l-fold symmetry, where the number of transparency windows increases with the beam’s orbital angular momentum (OAM). We investigate the effect of OAM on the propagation length of SPPs and analyze the penetration depth of SPPs within both the metallic and dielectric layers. Our results show that the penetration depth is minimized in regions where absorption is negligible, while the propagation length is maximized under these conditions.