Superluminal Optical Phase Conjugation: Pulse Reshaping and Instability
  We theoretically investigate the response of optical phase conjugators to incident probe pulses. In the stable (sub-threshold) operating regime of an optical phase conjugator it is possible to transmit probe pulses with a superluminally advanced peak, whereas conjugate reflection is always subluminal. In the unstable (above-threshold) regime, superluminal response occurs both in reflection and in transmission, at times preceding the onset of exponential growth due to the instability. 
M. Blaauboer, A.G. Kofman, A.E. Kozhekin, G. Kurizki, D. Lenstra, and   A. Lodder