Cooperatively enhanced light transmission in cold atomic matter
  We report enhanced transmission in measurements of the spectral dependence of forward light scattering by a high-density and cold ensemble of 87Rb atoms. This phenomenon, which is a result of dipole-dipole interaction induced cooperative light scattering in the atomic sample, implies a significant departure from the traditional density dependence of the transmitted light as embodied in the Beer-Lambert Law. Absolute values of the density-dependent forward light scattering cross-section are extracted from the measurements. 
Kasie Kemp, S.J. Roof, M.D. Havey, I.M. Sokolov and D.V. Kupriyanov
physics.atom-ph physics.optics quant-ph