Efficient Raman Sideband Generation in a Coherent Atomic Medium

Abstract

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 $Λ$ configuration on the D$_{1}$ line by two laser fields of resonant frequencies $ω_{1}$ and $ω_{2}$, and probed by a third field $% ω_{3}$. First-order sidebands for frequencies $ω_{1}$, $ω_{2}$ and up to the third-order sidebands for frequency $ω_{3}$ 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 ($ω_{1}-ω_{2}$), on the frequency $ω_{3}$ and on the optical density are investigated.