DEGENERATE PHASE-CONJUGATE 4-WAVE-MIXING IN A NEARLY-DOPPLER-FREE 2-LEVEL ATOMIC MEDIUM

We present experimental observations of phase-conjugate degenerate fou r-wave mixing in a two-level atomic system (the 3s S-2(1/2), F = 2, m( F) = 2 --> 3p P-2(3/2), F = 3, m(F) = 3 transition in a diffuse, colli sion-free, thermal beam of atomic sodium) driven by cw, narrow-band (s imilar to 250 kHz), stabilized pump and probe fields. The primary meas urements that we report are of the peak signal strength of the four-wa ve-mixing interaction and the bandwidth of the four-wave-mixing; spect rum (as the laser frequency is tuned through the resonant frequency) a s a function of the intensity of the pump field. We compare these meas urements with the predictions of a theoretical analysis in which exten sion to include the effect of the small transverse velocity (similar t o 3 m/sec) of the atomic beam is critical. These measurements provide a direct verification of the theory of this important nonlinear intera ction. [S1050-2947(98)06010-7].