Abstract

Here, we present a study on the dispersion features obtained in an electromagnetically induced transparency (EIT) experiment using a three-level cascade configuration in an $^{87}{\rm Rb}$ atomic vapor medium in the presence of Laguerre–Gaussian (LG) light as a coupling. A doublet transmission structure was obtained experimentally, and dispersion spectra were extracted using transmission spectra to study the probe light behavior. Dispersive regions that exhibit normal and anomalous nature were studied considering the polarization of various orientations as a coupling light. We established that normal dispersive region shows steep positive slopes, and anomalous dispersive region shows negative slopes, which can be controlled by polarization orientations. Owing to the change in the slopes of dispersion, normal and anomalous dispersive region is observed, and spectrum shows the effects of subluminal and superluminal propagation of probe light. This work, to the best of our knowledge, is novel in the study of dispersive region arising out of double-resonance EIT transmission spectra in the presence of LG light with the $l = 10$ and $p = 0$ mode as a coupling light with various polarization orientations. In the discussion, we establish that single parameter $\theta$ is sufficient for identifying the orientation and ellipticity of the polarization ellipse and also determine that the polarization of coupling light acts as a tuning parameter for changing the behavior of normal and anomalous dispersive region. Slow and fast light or superluminal propagation of probe light arise as a consequence of positive or negative group index, and fast light does not violate the principle of causality. Slow and fast light have future applications in high-speed quantum information and quantum communication using EIT-based protocol.

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