  We consider the simultaneous propagation of a pair of Raman-resonant,
frequency-modulated (chirped) laser pulses in an optically thick medium,
modeled by an ensemble of $\Lambda$-atoms. A self-organization ('matching`)
effect is shown for the chirped pulse pair, which leads to a quasi-lossless
propagation. Furthermore, we demonstrate that a well-defined coherent
superposition of the atomic ground states and, correspondingly, a coherence is
robustly created in the medium that can be controlled by amplitudes of the
laser pulses. The proposed scheme can be applied to substantially increase the
efficiency of the optical wave mixing processes, as well as in other nonlinear
processes where the initial preparation of a spatially extended medium in a
coherent superposition state is required.
