Controlling Raman gain with atomic coherence

Abstract

Raman gain is the optical gain generated by stimulated Raman scattering, which makes weak light amplify possible and can play an important role in weak light communication as well as related field. In this paper, experimentally and theoretically, we have observed the controllable Raman gain under the dressing effects in a coherently prepared N-type four-level atomic configuration. By controlling the detuning of the signal field and the coupling field, the electromagnetically induced transparency (EIT) window can be observed in the signal field. With the incidence of a strong pump laser into the atomic system, the two-photon ultranarrow fluorescence signal can overlap with EIT window by changing the frequency detuning of the pump field, meanwhile, a Raman gain can be induced by placing the signal field at possible large detuning. Such Raman gain can be effectively regulated and optimized by tuning the power of the signal field, pump field and the temperature of the atomic system so as to achieve higher contrast. The multi-parameter regulated higher contrast Raman gain with atomic coherence in atomic thermal system has potential applications in optical communication, superluminal laser and biophotonics.