Intensity Correlations And Coherence Effects In Resonance Fluorescence

Recently, studies of atom coherence and quantum interference effects are important frontier work in quantum optics and laser physics. They have led to many effects such as coherent population trapping (CPT), electromagnetic induced transparency, lasing without inversion and the modification of spontaneous emission. Much attention has also been paid to the effects of quantum coherence on the coherent manipulation of photon correlations. In this paper, we have studied atomic coherence and quantum interference effects on intensity correlation in three-level and four-level atom system. In different atom systems, the intensity correlation function takes extremely large values (much larger than 2) or remains below unity for a long time (many periods of oscillations or all times). In the present paper we refer to the former as "strong correlation" while to the latter as "anticorrelation".We have studied quantum interference effects on intensity correlation in three different atom systems. In the driven far off resonant three-level ladder configuration, we examine the intensity correlation functions of the two fluorescence fields that axe emitted from the top and middle states. We find that both of the fluorescence fields have anticorrelation when the applied fields are on two-photon resonance and far off one-photon resonances. In the other case, both of the fluorescence fields have strong correlations when the applied fields are far off one- and two-photon resonances. The phenomena are traced to the multiple interference mechanisms created in the system. Moreover, in the A three-level atom driven by a single coherence field, the fluorescence field shows strong correlation without quantum interference. This is in sharp contrast to the case of the V system. However, we find that the A system is equivalent to the V system in terms of dressed picture. The physical essential can be also attributed to quantum interference. By comparison, not only the V system but also the A system is operated near Coherent Population Trapping. Strong correlations of fluorescence field appear. In base of that, we extend the study on the intensity correlations for the driven cascade atom by taking the lower level splitting into account. It's shown when the lower A sub-system operates near CPT, strongly photons are produced from the two fluorescence fields emitted from the cascade transitions. For an appropriate choice of parameters, we have also anticorrelations for both, or strong correlation for one and anticorrelation for the other. We have found two cascade dressed transitions in presence of quantum interference. The phenomena are also traced to quantum interference.