A review of local field effects in lasing without inversion

We review the effects of density dependent near dipole-dipole, or local field, interactions on lasing without inversion. In particular, we consider the nonlinear behaviour of the macroscopic electric susceptibility of a dense, coherently prepared, three-level Lambda system. For certain values of the atomic density, we observe enhancement of the absorptionless index of refraction and inversionless gain by more than two orders of magnitude. We also predict a piezophotonic switching effect whereby a small change in density induces the system to flip from a strong absorber into a local field enhanced inversionless amplifier.