Gain-assisted superluminal light propagation via incoherent pump field
  We investigate the dispersion and the absorption properties of a weak probe field in a three-level Lambda-type atomic system. We use just an incoherent field for controlling the group velocity of light. It is shown that the slope of dispersion changes from positive to negative just with changing the intensity of the indirect incoherent pumping field. Gain-assisted superluminal light propagation appears in this system. No laser field is used in the pumping processes. 
M. Mahmoudi, S. Worya Rabiei, L. Safari, M. Sahrai