Effects of two strong fields in resonant four-wave mixing

An explicit solution is obtained for the four-wave mixing ω₄=ω₁−ω ₂+ω₃ of two strong fields E ₁, E ₃ and two weak fields E ₂, E ₄ in a four-level system with large Doppler broadening. Resonance of the intensity dependence of the mixing coefficient is found around equal Rabi frequencies, E ₁·d ₁=E ₃·d ₃, where d _1,3 are the dipole moments of the corresponding transitions. The effect is interpreted as a crossing of quasi-energy levels. Up to 6 peaks appear in the dependence of the conversion coefficient on the detuning of the probe field E ₂. The unexpected additional pair of peaks is a consequence of averaging over velocities. The results permit interpretation of the saturation behavior found in recent experiments on mixing in sodium vapor. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 777–782 (25 December 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.