The group index and its lineshape parameters of a relatively weak double-resonance probe pulse (signal) propagating through an open doubly driven M-type five-level atomic system are analytically formulated. It is shown for the first time, to our knowledge, that the group velocity status of the signal can be altered (between superluminal and subluminal propagation) by the combined effect of atomic coherence and linear AC Stark shift through coherent coupling. The distinct feature in this scheme is that, although it does not rely on electromagnetically induced transparency, a double-switching effect (i.e., from superluminal to subluminal and vice versa) is observed with negligible absorption/gain at two different frequency regimes.
© 2013 Optical Society of America
Lasers and Laser Optics
Original Manuscript: May 29, 2013
Revised Manuscript: July 17, 2013
Manuscript Accepted: July 31, 2013
Published: August 28, 2013
Saswata Ghosh, "Coherent double-switching between superluminal and subluminal propagation of probe pulse via AC Stark shift," J. Opt. Soc. Am. B 30, 2540-2548 (2013)