FWM in optically dense medía

We show, both experimentally and theoretically, that short-pulse reshaping clue to propagation leads to the formation of negative-time-delay signals in four-wave mixing (FWM) and to apparent signal decay that is not given by the dephasing or the population-decay rates. Recently, pulse reshaping due to coherent propagation was used to estimate dephasing times in CD, and ZnP·. (Ref. 1), and negative time-delay response in FWM in quantum wells was reported and was explained in terms of higher-order susceptibilities interfering with the third-order FWM process.2