  We propose an efficient scheme for the generation and the manipulation of
Raman fields in an homogeneously broadened atomic vapor in a closed three
levels $\Lambda$-configuration. The key concept in generating the Raman and
sub-Raman fields efficiently at lower optical densities involve the microwave
induced atomic coherence of the lower levels. We show explicitly that,
generation efficiency of the Raman fields can be controlled by manipulating the
coherences via phase and amplitude of the microwave field.
