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Open Physics

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

Ashfaq Uddin, Najm Uddin, Latif Ur Rahman, Zakir Khan, Ali Akgül

Published Jan 1, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1515/phys-2025-0301

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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.
Abstract We used a theoretical approach to study and investigate that how light pulses move faster than light in a four level atomic medium. In this study Laguerre-Gaussian (LG) beam waist, represented by F and strength Z is controlled. We examine the localized absorption and dispersion characteristics inside the four level atomic medium, illustrating that altering the beam waist affects the group velocity. According to the findings that we obtained, the group velocity at lower beam waists is between -0.0004c to -0.0002c, and the group index is negative, ranging from -0.0015 to -0.0005 respectively. As the pulse waist expands the extent of localized absorption and dispersion widens, yet the superluminal performance stays unchanged. Potentially useful in fields such as gravitational wave detection, soliton radar systems, and high-speed optical computing, this study sheds fresh information on the adaptability of light propagation in dispersive surfaces.
We studied and investigated whether light pulses travel faster then light in a four-level atomic medium using a theoretical method. Laguerre-Gaussian (LG) beam waist, denoted by F and strength Z, is regulated in this investigation. We analyses the localized absorption and dispersion properties within the four level atomic medium as well as demonstrate how the group velocity is affected by changing the beam waist. Our results showed that the team index remained negative, with values spanning -0.0015 to -0.0005, and the speed of the group at reduced beam-like waists was among -0.0004 and -0.0002 c. While the superluminal capability remains constant, the level of localized absorption as well as dispersion increases with the pulse waist. This work provides new insights into the flexibility of light propagation on dispersive surfaces, which may be helpful in domains like gravitational wave motion detection methods, soliton scanning systems, and high-frequency optical computation.
We studied and investigated whether light pulses travel faster then light in a four-level atomic medium using a theoretical method. Laguerre-Gaussian (LG) beam waist, denoted by F and strength Z, is regulated in this investigation. We analyses the localized absorption and dispersion properties within the four level atomic medium as well as demonstrate how the group velocity is affected by changing the beam waist. Our results showed that the team index remained negative, with values spanning -0.0015 to -0.0005, and the speed of the group at reduced beam-like waists was among -0.0004 and -0.0002 c. While the superluminal capability remains constant, the level of localized absorption as well as dispersion increases with the pulse waist. This work provides new insights into the flexibility of light propagation on dispersive surfaces, which may be helpful in domains like gravitational wave motion detection methods, soliton scanning systems, and high-frequency optical computation.
We studied and investigated whether light pulses travel faster then light in a four-level atomic medium using a theoretical method. Laguerre-Gaussian (LG) beam waist, denoted by F and strength Z, is regulated in this investigation. We analyses the localized absorption and dispersion properties within the four level atomic medium as well as demonstrate how the group velocity is affected by changing the beam waist. Our results showed that the team index remained negative, with values spanning -0.0015 to -0.0005, and the speed of the group at reduced beam-like waists was among -0.0004 and -0.0002 c. While the superluminal capability remains constant, the level of localized absorption as well as dispersion increases with the pulse waist. This work provides new insights into the flexibility of light propagation on dispersive surfaces, which may be helpful in domains like gravitational wave motion detection methods, soliton scanning systems, and high-frequency optical computation.
Superluminal propagation of light is a well-established phenomenon and has motivated immense research interest that has led to state-of-the-art knowledge and potential applications in the emerging technology of quantum optics and photonics. This study presents a theoretical analysis of the gain-assisted superluminal light propagation in a four-level NNN-type atomic system by exploiting the scheme of electromagnetically induced gain and superluminal propagation of surface plasmon polaritons (SPPs) along the gain-assisted atomic-metal interface simultaneously. In addition, a theoretical demonstration is presented on the comparison between Fresnel's rotary photon drag and SPP drag in view of light polarization state rotation by rotating the coherent atomic medium and the atomic-metal interface, respectively. Analogous to photon drag in the superluminal anomalous dispersion region where light polarization rotation occurs opposite the rotation of the gain-assisted atomic medium, the rotation of the atomic-metal interface also rotates the polarization state of SPPs opposite the rotation of the interface. This further confirms the superluminal nature of SPPs propagating along the interface with negative group velocity. Rabi frequencies of the control and pump fields considerably modify both photon and SPP drag coefficients. Metal conductivity also controls SPP propagation.
We studied and investigated whether light pulses travel faster then light in a four-level atomic medium using a theoretical method. Laguerre-Gaussian (LG) beam waist, denoted by F and strength Z, is regulated in this investigation. We analyses the localized absorption and dispersion properties within the four level atomic medium as well as demonstrate how the group velocity is affected by changing the beam waist. Our results showed that the team index remained negative, with values spanning -0.0015 to -0.0005, and the speed of the group at reduced beam-like waists was among -0.0004 and -0.0002 c. While the superluminal capability remains constant, the level of localized absorption as well as dispersion increases with the pulse waist. This work provides new insights into the flexibility of light propagation on dispersive surfaces, which may be helpful in domains like gravitational wave motion detection methods, soliton scanning systems, and high-frequency optical computation.