  We demonstrate the efficient generation of Raman sidebands in a medium
coherently prepared in a dark state by continuous-wave low-intensity laser
radiation. Our experiment is performed in sodium vapor excited in $\Lambda $
configuration on the D$_{1}$ line by two laser fields of resonant frequencies
$\omega_{1}$ and $\omega_{2}$, and probed by a third field $% \omega_{3}$.
First-order sidebands for frequencies $\omega_{1}$, $\omega_{2}$ and up to the
third-order sidebands for frequency $\omega_{3}$ are observed. The generation
starts at a power as low as 10 microwatt for each input field. Dependencies of
the intensities of both input and generated waves on the frequency difference
($\omega_{1}-\omega_{2}$), on the frequency $\omega_{3}$ and on the optical
density are investigated.
