Gain spectrum of a laser-driven Λ-type atom with vacuum-induced coherence

Abstract

We examine the gain spectrum of a coherently driven Λ-type atom with a pair of closely lying ground levels, where a single laser field drives both transitions from the upper state to the lower states simultaneously. The effects of vacuum-induced coherence among decay channels are taken into account. Gain spectra under various conditions are presented and analyzed. We show that the spectral structure and the gain amplitude of the probe are strongly influenced by the vacuum-induced coherence as well as the frequency separation between the two ground levels. We present an explanation to our numerical results by introducing dipole moments in the dressed-state representation.