Optical gain properties in a coherently prepared four-level cold atomic system

Abstract

We analyze the optical gain property of a probe pulse in a four-level system of ultracold $^{87}\mathrm{Rb}$ atoms prepared via a stimulated Raman adiabatic passage type process. During the process of preparation, most population is transferred from the ground state to the highest excited state by two driving pulses in the counterintuitive order. Thus population inversion can be achieved between the highest state and a lower-lying state in a suitable period of time, which then allows very large gain for the probe pulse applied after the driving pulses. In particular, we investigate in detail the influence of several interaction parameters of interest on the probe gain via numerical simulation and qualitative analysis.