Eur. Phys. J. Plus (2025) 140: 922
https://doi.org/10.1140/epjp/s13360-025-06854-4

Regular Article

Tunable control of birefringent sub-luminal to super-luminal propagation of structured light in a chiral medium

¹ Department of Applied Physics and Materials Sciences, University of Swat, Swat, KP, Pakistan
² Quantum Optics and Quantum Information Research Group, University of Malakand, Malakand, KP, Pakistan

^a kefsayed@uswat.edu.pk

Received: 7 April 2025
Accepted: 13 September 2025
Published online: 26 September 2025

Abstract

This work explores birefringent sub-luminal and super-luminal structured light propagation in a chiral atomic medium. The study investigates how structured light affects left circularly polarized (LCP) and right circularly polarized (RCP) probe beams through azimuthal quantum number-dependent control fields. Control fields carrying topological charges are used to manipulate the absorption, dispersion, and propagation speeds of LCP and RCP beams. The effects of varying topological charges on these optical properties are analyzed. Specifically, positive and negative group indices for RCP and LCP beams are examined within the range of $-4\times {10}^5\le n_g^{(R,L)}\le 4\times {10}^5$. Variations in sub-luminal and super-luminal propagation are studied within the velocity range of $-c/4\times {10}^5\le v_g^{(R,L)}\le c/4\times {10}^5$. For $l=n,n$ distinct sub-luminal and super-luminal propagation regions are observed. Increasing the value of l enhances super-luminality, while decreasing l enhances sub-luminality. These variations significantly impact the control of light propagation in the medium. The findings provide insights into structured light control in a chiral atomic medium and have potential applications in information storage devices, imaging, and time-cloaking technology.