Photonic Band Gaps in One-Dimensionally Ordered Cold Atomic Vapors
  We experimentally investigate the Bragg reflection of light at one-dimensionally ordered atomic structures by using cold atoms trapped in a laser standing wave. By a fine tuning of the periodicity, we reach the regime of multiple reflection due to the refractive index contrast between layers, yielding an unprecedented high reflectance efficiency of 80%. This result is explained by the occurrence of a photonic band gap in such systems, in accordance with previous predictions. 
Alexander Schilke, Claus Zimmermann, Philippe W. Courteille, William   Guerin
physics.atom-ph physics.optics