SPECTRAL LINE NARROWING IN ELECTROMAGNETICALLY INDUCED TRANSPARENCY

Electromagnetically induced transparency (EIT) can make an otherwise opaque medium transparent by utilizing quantum coherence. EIT has attracted great interest since the 1990s for its wide applications in metrology, nonlinear and quantum optics, and quantum information science. We present a review on spectral line narrowing mechanisms in EIT-related systems, accounting for linewidths much narrower than expected from the standard mechanisms of Doppler broadening, transit time broadening, magnetic field inhomogeneity and power broadening. Topics covered include Dicke narrowing, atomic-motion-induced Ramsey narrowing, motional narrowing, density narrowing, laser induced narrowing and power-broadening-free resonance. Intuitive pictures are provided to describe the essential physics of each mechanism.

SPONTANEOUS EMISSION SPECTRA AND SIMULATING MULTIPLE SPONTANEOUSLY-GENERATED COHERENCE IN AN N-TYPE MEDIUM

We investigate the spontaneous emission spectra of a coherently driven four-level cold atomic system. It is shown that a few interesting phenomena such as spectral-line narrowing, spectral-line enhancement, spectral-line suppression, and spontaneous emission quenching can be realized in our system. The spectral-line enhancement and suppression can be conveniently manipulated by appropriately modulating the frequency detuning of the probe driving field. In the dressed-state picture of the probe and coupling fields, we find that this coherently-driven atomic system has three close-lying levels so that multiple spontaneously-generated coherence (SGC) arises. Our considered atomic model can be found in real atoms, such as rubidium or sodium, so a corresponding experiment can be done to observe the expected phenomena related to SGC effect, since no rigorous conditions are required.