  A theoretical investigation on the quantum control of optical coherent
four-wave mixing interactions in two-level systems driven by two intense
synchronized femtosecond laser pulses of central angular frequencies $\omega$
and $3\omega$ is reported. By numerically solving the full Maxwell-Bloch
equations beyond the slowly-varying envelope and rotating-wave approximations
in the time domain, the nonlinear coupling to the optical field at frequency
$5\omega$ is found to depend critically on the initial relative phase $\phi$ of
the two propagating pulses; the coupling is enhanced when the pulses interfere
constructively in the center ($\phi=0$), while it is nearly suppressed when
they are out of phase ($\phi=\pi$). The tuning of the initial absolute phase of
the different frequency components of synchronously propapagating
$\omega$-$3\omega$ femtosecond pulses can serve as a means to control coherent
anti-Stokes Raman scattering (CARS) processes.
