DIPOLE-DIPOLE BROADENED LINE-SHAPE IN A PARTIALLY EXCITED DENSE ATOMIC GAS

We have experimentally investigated the resonance line shape of a part ially excited dense atomic rubidium vapor at a density where the binar y collision approximation starts to break down. The overall spectral s hape is well represented by a simple expression for the dielectric fun ction that includes an excitation-dependent linewidth and shift. The r esults for the excitation dependence of the linewidth agree with an es timate based on a quasistatic picture of the collisions.