SPPs-enhanced Laguerre field-dependent superluminal propagation in atomic media

Abstract

Motivated by the need for controllable fast-light platforms in compact photonic systems, this work investigates surface plasmon polariton (SPP)-assisted superluminal group propagation in a four-level cesium atomic medium driven by Laguerre-Gaussian control fields. The aim is to examine how the beam waist and intensity of the structured control fields, together with plasmonic field confinement, modify absorption, dispersion, group index, and group velocity. Using a density-matrix formulation, the probe-field coherence is obtained, the optical susceptibility is calculated, and the group velocity is evaluated from the dispersion slope while the SPP contribution is included through the effective dielectric response. The results show that increasing the Laguerre-Gaussian beam waist broadens the spatial region of anomalous dispersion and negative group index, while SPP confinement strengthens the local atom-field interaction and enhances susceptibility modulation. The study demonstrates a tunable route for controlling localized superluminal group propagation without implying superluminal information transfer, with potential applications in optical switching, photonic signal processing, plasmonic sensing, and quantum optical devices.