Multiresonant behavior in nearly degenerate four-wave mixing: the ac Stark effect

We have experimentally studied the effects of pump-probe detuning in nearly degenerate four-wave mixing. The data show multiresonant behavior as a function of the pump-probe detuning at both low and high intensities. At low intensities, the structure is the result of Doppler motion. At high intensities, five-peak structure is observed and is explained by the standing-wave modulation of the ac Stark splitting of the atomic levels.