Abstract

Three (or many)-level atoms interacting with two (or more) classical electromagnetic fields are often studied in the steady state and weak field probe approximation. This approximation is generally not suitable for quantized field, where all modes of electromagnetic fields contain a few photons or especially where the coupling mode is in vacuum. In this article, upper-coupling and lower-coupling, master equations of a three-level cascade atom, interacting with a couple of quantized electromagnetic field are exactly solved in the steady state and zero detuning coupling field. The atomic population of levels and its absorption and dispersion are investigated. A comparison between the exact and the corresponding weak field approximation methods is presented.