The Atomic Lighthouse Effect
  We investigate the deflection of light by a cold atomic cloud when the light-matter interaction is locally tuned via the Zeeman effect using magnetic field gradients. This "lighthouse" effect is strongest in the single-scattering regime, where deviation of the incident field is largest. For optically dense samples, the deviation is reduced by collective effects, as the increase in linewidth leads to a decrease of the magnetic field efficiency. 
C. E. M\'aximo, R. Kaiser, Ph.W. Courteille, R. Bachelard
physics.atom-ph