Light amplification mechanisms in a coherently coupled atomic system

We analyze transient properties of light amplification in a coherently coupled three-level {Λ}-type system and study the system evolution from the transient regime into the steady state. From the time evolution of the atomic coherence and population distribution, we discuss the transient light amplification mechanism with and without population inversion. We also solve the density-matrix equations in the steady state and derive the conditions for the existence of specific light amplification mechanisms, such as light amplification without inversion in any standard state basis, light amplification by stimulated Raman scattering, and light amplification from population inversion in the dressed states.