Coherent flash of light emitted by a cold atomic cloud
  When a resonant laser sent on an optically thick cold atomic cloud is abruptly switched off, a coherent flash of light is emitted in the forward direction. This transient phenomenon is observed due to the highly resonant character of the atomic scatterers. We analyze quantitatively its spatio-temporal properties and show very good agreement with theoretical predictions. Based on complementary experiments, the phase of the coherent field is reconstructed without interferometric tools. 
Maryvonne Chalony (INLN), Romain Pierrat (ESPCI), Dominique Delande   (LKB - Jussieu), David Wilkowski (INLN, CQT)
physics.atom-ph physics.optics