We demonstrate novel four-wave mixing processes in a cold vapor that arise due to atomic spatial self-organization. This leads to a reduced parametric oscillation threshold and a more rapid increase of gain with pump power.
In this work, we explore both the internal and external atomic degrees of freedom to demonstrate the observation of giant gain and parametric oscillation in multiple four-wave mixing (FWM) processes in a sample of cold cesium atoms. We employ a standard backward FWM beam configuration to achieve parametric probe-beam gains exceeding 2000. This giant gain is accompanied by the generation of three other beams of equivalent power emitted along the directions satisfying the phase-matching conditions for multiple cascade forward and backward FWM triggered by the incident probe and the counterpropagating pumping beams. Moreover, we have also observed a simultaneous threshold for parametric oscillation of the four coupled optical fields with the pump intensity. These results point to an alternative pathway to generate multipartite correlated optical fields associated with long-lived atomic systems for applications in quantum information.