  This work presents a theoretical analysis of the Autler-Townes splitting
pattern in the four-wave mixing signal generated in a three-level cascade
Doppler-broadened system. We employ the density matrix formalism to write the
Bloch equations and solve them numerically. The solutions allow us to compare
the response of the upper level population and the generated signal coherence
for homogeneously and non-homogeneously broadened systems. Our results reveal
an AC Stark shift in the nonlinear signal when the frequency of the strong or
weak beam is scanned, in contrast to what is observed in the fluorescence.
Furthermore, we present experimental data for the four-wave mixing signal in a
hot rubidium vapor for the copropagating configuration of the exciting beams.
The behavior of the AC Stark displacement and signal amplitude as a function of
laser power indicates a good agreement between the model and the experimental
results.
