Key points are not available for this paper at this time.
An atomic transition that has been made transparent by applying an additional electromagnetic field exhibits a rapidly varying refractive index with zero group velocity dispersion at line center. A 10-cm-long Pb vapor cell at an atom density of 710^15 atoms/cm^3 and probed on its 283-nm resonance transition has a calculated optical delay of 83 ns (c/V₆) =250.
Harris et al. (Wed,) studied this question.