Optical properties of an N-type system in Doppler-broadened multilevel atomic media of the rubidium D2 line

We report the observations of Mollow sideband-like transparency windows in a Doppler-broadened four-level N-type system of the rubidium D2 line. A pair of enhanced transparency windows across an electromagnetically induced transparency line centre results from dressed state interactions of two coupling fields. The present observations have potential applications of using the symmetric transparency windows for optical quantum information processing such as multiple optical buffer memories and double slow-light-based enhanced cross-phase modulation. We also discuss the quantum coherent control of absorption cancellation, absorption enhancement and probe gain in a closed N-type four-level model introducing the atom flow rate determined by the population decay rate and control field intensity.