Modification of local field effects in two level systems due to quantum corrections.
Quantum corrections to the Lorentz{Lorenz formula are given for a dense ensemble of atoms interacting with the quantized radiation field. The in uence of these corrections on local-field effects in two-level systems is discussed in the non-cooperative limit. For initially inverted atoms we find superluminescence and radiation trapping. Furthermore it is shown that the quantum corrections set strong limitations to intrinsic optical bistability.