Parametric processes in a system of three-level atoms

A theoretical investigation is made of four-photon parametric interactions in a medium composed of threelevel atoms. The presence of the third level, associated with the doublet splitting of the excited state, gives rise to new regions of exponential parametric amplification. A study is made of the change in the value of the gain and its spectral range due to variation of the frequency of a strong wave participating in the parametric interaction.