Sub-natural linewidth resonances in coherently-driven double e??? system

摘要

We investigate theoretically the pump-probe spectroscopy of coherently-driven four-level e??? system with two closely spaced excited common levels, thereby forming a double e??? system. Using the master equation approach, analytical results are obtained for the absorption spectrum of a weak probe in the presence of a strong pump. The model is applied to the double e??? system 52 e?‘?1/2 e??1 = 1, 2 a?’ 52e?‘?3/2 e??1' = 1, 2 of 87Rb atom. It is shown that the absorption spectrum consists of a triplet, of which one resonance is of sub-natural linewidth depending on the atoma€“field interaction parameters. The effect of Doppler broadening on the absorption spectrum is also investigated.