We study the generation of coherence of a nonallowed transition by a Raman scattering process in
a three-level system. We present analytical and numerical solutions of the density-matrix equations in steady
state. We study the conditions for maximizing the coherence. We find that, when the system is far off
resonance and the fields and the coupling are not too strong, the problem of coherence in the three-level
system reduces to that in an effective two-level model, and the maximal coherence generated in steady state
is limited by the steady-state two-level-model value ?1/(2??2). We show that when the amplitudes of the
fields are sufficiently high that the system is far beyond the strong-coupling regime, the coherence of the
nonallowed transition can reach its stationary maximum value -1/2. We study the difference between the
wave-vector shifts of the two fields, and examine the possibility of stationary induced transparency and
matched pulses. ?? 1999 The American Physical Society.
