Tunable superluminal propagation at spectral hole-burning regions in magneto-optical atomic medium

In the context of spectral hole-burning, normal dispersion with subluminal propagation is usually observed in the spectral hole-burning depth region. However, anomalous dispersion can occur in the continuous absorption peak region, which leads to superluminal light propagation. In this paper, we report an unusual behaviour of dispersion at discontinued absorption kink regions. We demonstrate both normal dispersion at the kink absorption region and anomalous dispersion at the spectral hole-burning depth region. The unusual dispersion leads to a positive group index in the absorption kink region and a negative group index in the spectral hole-burning depth region. The spectral hole-burning is due to variation of magnetization rather than the molecular distribution. The outcomes of our work offer promising applications in communication technologies and storage devices.