RESONANT DEGENERATE 4-WAVE-MIXING IN DENSE MEDIA

In this paper we analyze theoretically the influence of the local-fiel d effects on reflection spectra of a degenerate four-wave mixing in a dense medium of two-level atoms. We discuss the spectral dependence of the nonlinear absorption and dispersion of the signal and probe field s as well as their coupling for various strengths of the external fiel d and atomic densities. For weak external fields the local-field effec ts reduce to the well known Lorentz redshift of the reflection spectra . When the external field saturates the transition in a dense sample s ignificant modifications of the probe reflectivity and of the wave mix ing spectra occur, resulting in asymmetric, multipeak line shapes.