Quantum jumps in a coherently driven Raman system

Early results of Agarwal and Jha [Z. Phys. B 35, 391 (1979)] are used to examine the question of quantum jumps in a Raman (Λ) system driven by two coherent fields. We discuss both short-time (${\gamma }_1$t≲1) and long-time (${\gamma }_2$t≊1) behavior of the intensity correlations assuming that the Stokes transition is very weak, ${\gamma }_2$≪${\gamma }_1$. We calculate the counting statistics of the dark periods using the higher-order intensity correlations. The results differ from those obtained using arguments based on population trapping which predict only a very rare ‘‘jump’’ event. The intermittence in fluorescence produced by a coherently driven Λ system is interpreted in terms of an equivalent two-state Markov process.