Coherently induced shifting of group index across the triple atomic transition lines in Double-N-type system

Abstract

The group index and its corresponding absorption of a propagating probe pulse across three atomic transition lines is theoretically presented for a Double-N-type non-EIT scheme. We have shown that, group index on the three transition lines can be shifted accordingly to control the status (superluminal/subluminal) of the pulse propagation with reduced absorption/gain by controlling the relative strength of coherent coupling. The analytical expression of effective detuning clearly exhibits the nature of linear AC Stark shift responsible for shifting/switching of group index on three different probe transition frequency regimes.