Numerical simulations of light propagation in a dense near-resonant gas

We study light propagation in a dense gas numerically by applying classical electrodynamics to a collection of near-resonant atoms regarded as point dipoles. In the limit when the atom density and the wave number of light satisfy $\rho k^{-3}\ge 1$, dipole-dipole interactions may make the system strongly correlated, whereupon the mean-field type approximations underlying traditional electrodynamics of polarizable media become invalid. In a dense homogeneously broadened sample both the Lorentz-Lorenz local-field shift and the cooperative Lamb shift are absent, but a more conventional phenomenology reemerges in both dilute and inhomogeneously broadened samples.