Three-level waterfall system.

If one of the fields is intense, either in the bottom transition or in the top transition, it is possible to see the Autler-Townes doublet.

The level structure with Stark shifts is shown when at least one of the fields is weak ($\Omega/\pi < 1$ MHz), since the unfolding of levels is very complicated when both fields are intense.

The graphical solution is shown based on the algebraic solution of Bloch's equations in the steady state [1].

The Stark displacements of the levels from their original positions are given by [2]

$$ \omega_{\pm} = \dfrac{\delta - kv}{2} \pm \dfrac{1}{2} \sqrt{ 4\Omega^2 + (\delta-kv)^2}, $$

where $\delta$, $\Omega$ and $k$ are the detuning, Rabi frequency and the strong field wavenumber, and $v$ is the component of the atom's velocity in the direction of the strong field.

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