Investigation of multipass geometries for efficient degenerate four-wave mixing in Nd:YAG

Degenerate four-wave mixing in the saturable gain of a flash-lamp-pumped Nd:YAG amplifier has been investigated. Three different geometries are examined in which the probe beam experiences (a) one pass, (b) two passes, and (c) four passes of the four-wave interaction region. It is found that multipassing the gain medium has a dramatic effect on the efficiency of the process, with a phase-conjugate reflectivity of 2500 and a conjugate energy extraction efficiency of greater than 200% demonstrated.