Influence of population transfer on parametric four-wave mixing in sodium vapor

The authors examine the effects of population transfer on parametric four-wave mixing (PFWM) in Na vapor. They show experimentally that during the laser pulse the phase-matching conditions necessary for the generation of axial PFWM are destroyed by population transfer. Shortening of the PFWM pulse with respect to the laser pulse length is observed. By the use of counterpropagating laser beams wherein the degree of temporal and spatial overlap in the medium is controlled, the authors show how simple measurements can provide direct evidence of population transfer spoiling of PFWM production.