Even with incoherent driving, coherence effects may show up in the spontaneous emissions of an atom. We derive a general master equation and predict that for both the three-level V and Λ systems the intensity correlation function ${\mathit{g}}^{\mathrm{}\left(2\right)\mathrm{}}$(τ) may exhibit pronounced oscillations with frequency δω if the level separation ħδω is small. We obtain a marked difference in the beat amplitude for a single Λ system as compared to a beam or gas. If δω is much smaller than the natural linewidth we find dark and light periods in the spontaneous emission.

• Received 6 July 1992

DOI:https://doi.org/10.1103/PhysRevA.47.2186