In an open /\ type system with the spontaneously generated coherence (SGC), when the probe and driving fields have different frequencies, the switching of the group velocity of the probe pulse from subluminal to superluminal is realized not only by adjusting values of the relative phase between the probe and driving fields but also by varying values of the incoherent pumping rate. For the subluminal propagation, the system always exhibits the probe absorption, however, the superluminal propagation is always companied with gain of the probe field.
© 2005 Chinese Optics Letters
Ni Cui, Aiyun Li, Hui Ma, Hua Li, and Xijun Fan, "Manipulation role of the relative phase and incoherent pumping on a light pulse propagation," Chin. Opt. Lett. 4, 240-242 (2006)