Phase-conjugate four-wave mixing with partially coherent laser fields

We present results of our experimental investigations of phase-conjugate fo ur-wave mixing in a nearly Doppler-free, collisionless, two-level quantum s ystem with a partially coherent non-Markovian laser field. The two componen ts of the laser field-an intense pump and a weak, time-delayed probe-are de rived from a single narrow-band cw laser source on which phase and frequenc y fluctuations conforming to the phase diffusion model are superimposed. We carry out these measurements using the D-2 transition in an optically pump ed diffuse beam of atomic sodium. We vary the pump intensity, laser bandwid th, and temporal delay between the pump and probe, and measure the peak sig nal strength, the bandwidth, and the asymmetry of the four-wave-mixing spec trum. For comparison with our experimental results of the peak signal stren gth, we also analyze the same interaction numerically, through direct integ ration of the optical Bloch equations. The numerical results are in good ag reement with the measurements. [S1050-2947(99)00307-8].