Observation of suppression of light scattering induced by dipole-dipole   interactions in a cold atomic ensemble
  We study the emergence of collective scattering in the presence of dipole-dipole interactions when we illuminate a cold cloud of rubidium atoms with a near-resonant and weak intensity laser. The size of the atomic sample is comparable to the wavelength of light. When we gradually increase the atom number from 1 to 450, we observe a broadening of the line, a small red shift and, consistently with these, a strong suppression of the scattered light with respect to the noninteracting atom case. Numerical simulations, which include the internal atomic level structure, agree with the data. 
J. Pellegrino, R. Bourgain, S. Jennewein, Y.R.P. Sortais, S.D. Jenkins   and J. Ruostekoski and A. Browaeys
physics.atom-ph cond-mat.quant-gas quant-ph