Effect of finite bandwidth on refractive-index enhancement and lasing without inversion

We have studied the effect of finite bandwidth of the driving field on the enhancement of refractive index and lasing without inversion in a three-level atomic system in which partial coherence is introduced either in upper-level or lower-level doublet via a strong microwave driving field having finite bandwidth. We find that both phenomena are adversely affected by the phase fluctuations in the driving field. Further, there is a range of driving field detuning for which the refractive index is considerably enhanced with vanishing absorption.