Direct Optical Excitation of Quantum-Degenerate Exciton States in   Semiconductors
  Quantum electrodynamic calculations predict that truly incoherent light can be used to efficiently generate quantum-degenerate exciton population states. Resonant incoherent excitation directly converts photons into excitons with vanishing center of mass momentum. The populated exciton state possesses long-range order, is very stable against perturbations, and should be observable via its unusual directional and density dependence in luminescence measurements. 
M. Kira, S.W.Koch, G. Khitrova, and H.M. Gibbs