Response of the probe gain with or without inversion to the relative phase of two coherent fields in a three-level V model

Abstract

We investigate a V-type three-level atomic system with two near-degenerate excited levels, which is driven by a strong coherent field and a weak probe field. We find that, due to the quantum interference between two spontaneous decay channels, even in the absence of an incoherent pumping, the probe gain can be achieved and modulated at different probe detunings just by tuning the relative phase between the probe and the coherent field to different regions. By demonstrating the gain-absorption coefficient as well as the population difference on the probe transition, we show that the probe gain can be either with or without population inversion, which depends on detunings, spontaneous decay rates, and the relative phase. In this atomic system, the phase-dependent probe gain originates from the internal quantum interference effect as well as the external dynamically induced coherence effect.