Influence of a repump laser on a nearly degenerate four-wave-mixing   spectrum in atomic vapors
  The influence of a repump laser on a nearly degenerate four-wave-mixing (NDFWM) spectrum was investigated. We found the amplitude and line shape of the NDFWM depended strongly on the detuning of the repump field. A five-peak structure was observed. And at some certain repump detuning a dip appeared at the central peak. A rough analysis was proposed to explain this effect. 
Wei Jiang, Qun-feng Chen, Yong-sheng Zhang and G. -C. Guo