Near dipole-dipole effects in lasing without inversion: An enhancement of gain and absorptionless index of refraction

We include the effect of density-dependent near dipole-dipole interactions in order to generalize the theory of a simple three-level system that exhibits lasing without inversion and an enhanced index of refraction at zero absorption. For certain values of atomic density, our generalized theory predicts a novel enhancement of inversionless gain and absorptionless index by more than 2 orders of magnitude.