Theory of degenerate four-wave mixing in three-level atoms

We derive a theoretical model for phase conjugation in three level atoms. The atoms are assumed to be at rest and the intensities I₁ and I₂ of the pump beams can take arbitrary large values. We calculate the lineshape for a thin optical medium in the case of plane waves and of gaussian beams. In the case of a thick optical medium, we show that the gain saturates if I₁ ≠ I₂.