Microscopic Lensing by a Dense, Cold Atomic Sample
  We demonstrate that a cold, dense sample of 87Rb atoms can exhibit a micron-scale lensing effect, much like that associated with a macroscopically-sized lens. The experiment is carried out in the fashion of traditional z-scan measurements but in much weaker fields and where close attention is paid to the detuning dependence of the transmitted light. The results are interpreted using numerical simulations and by modeling the sample as a thin lens with a spherical focal length. 
Stetson Roof, Kasie Kemp, Mark Havey, I.M. Sokolov, and D.V.   Kupriyanov
physics.atom-ph physics.optics quant-ph