Anomalous dispersion properties of an atomic medium with a closed excitation contour

This paper examines the refractive index dispersion in an atomic medium with a closed excitation contour. The refractive index as a function of the algebraic sum of the phases of excitation fields (Φ) and Rabi frequencies is shown to have a maximum for Φ ≤ π/4. A frequency range is found near the maximum where an increase in refractive index is accompanied by amplification of one of the optical fields.