Comments on Superluminal Laser Pulse Propagation
  Researchers claim to have observed superluminal (faster than light) propagation of a laser pulse in a gain medium by a new mechanism in which there is no distortion of the pulse [Nature, 406, 277 (2000)]. Our analysis shows that the observed mechanism is due to pulse distortion arising from a differential gain effect and should not be viewed as superluminal propagation. 
P. Sprangle, J.R. Penano, B. Hafizi