Electromagnetically induced transparency and Autler-Townes splitting: Two similar but distinct phenomena in two categories of three-level atomic systems

Electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting are two phenomena that could be featured in a variety of three-level atomic systems. The considered phenomena, EIT and AT, are similar “looking” in the sense that they are both characterized by a reduction in absorption of a weak field in the presence of a stronger field. In this paper, we explicitly set the threshold of separation between EIT and AT splitting in a unified study of four different three-level atomic systems. Two resonances are studied and compared in each case. A comparison of the magnitudes of the resonances reveals two coupling-field regimes and two categories of three-level system.

Figure 1

Three-level atomic systems. $W_{\mathit{ij}}$ is the population decay rate from level $i$ to level $j$. ${\Omega }_p$ and ${\Omega }_c$ denote the Rabi frequencies of the probe and coupling fields, respectively. ${\delta }_p$ is the detuning of the probe field. The coupling field is at resonance.

Figure 2

Negative absorption coefficient of the probe field as a function of its detuning. The dip (reduction in absorption) could be a signature of EIT or AT coupling. This is a general plot added for qualitative reasons only.

Figure 3

Relative magnitudes of the two resonances [Eqs. (2) ($\Lambda$), (5) (cascade-EIT), (8) (cascade-AT), and (11) ($\mathsf{V}$)] as functions of the threshold factor ${\Omega }_c/{\Omega }_t$ [Eqs. (13a, 13b, 13c, 13d)].

Figure 4

Evolution of the resonances as functions of decreasing (a)–(d) threshold factor in the $\Lambda$ case [Fig. 1a]. Each subplot includes the first resonance, second resonance, and total absorption of the probe field as a function of its detuning.

Figure 5

Evolution of the resonances as functions of the decreasing (a)–(d) threshold factor in the $\mathsf{V}$ case [Fig. 1d]. Each subplot includes the first resonance, second resonance, and total absorption of the probe field as a function of its detuning.