  Four-wave mixing in resonant atomic vapors based on maximum coherence induced
by Stark-chirped rapid adiabatic passage (SCRAP) is investigated theoretically.
We show the advantages of a coupling scheme involving maximum coherence and
demonstrate how a large atomic coherence between a ground and an highly excited
state can be prepared by SCRAP. Full analytic solutions of the field
propagation problem taking into account pump field depletion are derived. The
solutions are obtained with the help of an Hamiltonian approach which in the
adiabatic limit permits to reduce the full set of Maxwell-Bloch equations to
simple canonical equations of Hamiltonian mechanics for the field variables. It
is found that the conversion efficiency reached is largely enhanced if the
phase mismatch induced by linear refraction is compensated. A detailed analysis
of the phase matching conditions shows, however, that the phase mismatch
contribution from the Kerr effect cannot be compensated simultaneously with
linear refraction contribution. Therefore, the conversion efficiency in a
coupling scheme involving maximum coherence prepared by SCRAP is high, but not
equal to unity.
