EFFICIENT LOW-INTENSITY OPTICAL-PHASE CONJUGATION BASED ON COHERENT POPULATION TRAPPING IN SODIUM

We have observed optical phase-conjugate gain (>50) in sodium vapor, u sing low-intensity pump lasers(1 W/cm(2)), with a response time of the order of 1 mu s. Coherent population trapping is experimentally ident ified as the phase-conjugate mechanism. A theoretical model is present ed that supports these observations by showing that coherent populatio n trapping can write large-amplitude nonlinear-optical gratings at las er intensities well below those needed to saturate the optical transit ions.