EFFECT OF FINITE BANDWIDTHS OF PROBE AND DRIVING FIELDS ON REFRACTIVE-INDEX AND GAIN IN A RAMAN-DRIVEN 4-LEVEL SYSTEM

We discussed the conditions for realizing maximum index of refraction without absorption of the light and analyzed the effect of the finite bandwidths of the probe and driving field on the index of refraction a nd the gain in a Raman-driven four-level system. We found that the max imum index of refraction with vanishing absorption can be achieved by changing the intensity of the driving field or changing the detuning b etween the frequency of the driving held and the resonant atomic trans ition. The finite bandwidths of the driving held and the probe field c ould destroy the coherence of atoms, decrease the gain and change the value of the index of refraction.