The Onset of Matter-Wave Amplification in a Superradiant

The interaction of short and strong laser pulses with an atomic Bose-Einstein condensate is found to generate patterns of recoiling atoms that are different from those seen in previous light-scattering experiments. This phenomenon can only be explained by optical stimulation, showing that the previous description of superradiance as atomic stimulation is incomplete and that matter-wave amplification in Bose-Einstein condensates is suppressed at short times. Our experiments clarify the nature of bosonic stimulation in the four-wave mixing of light and atoms. Superradiance is the collective emission of light from an ensemble of excited atoms and involves the spontaneous buildup of coher-ence in a macroscopic ensemble of atoms. Dicke, in his seminal work (1), showed that the spontaneous emission of photons from an ensemble of N localized atoms is enhance