Picosecond superradiance in a three-photon resonant medium
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We investigate picosecond cooperative emission in an ensemble of rubidium atoms coherently excited by 100-fs laser pulses that are three-photon resonant to the 6P-5S transition. The emitted 420-nm light is recorded by a streak camera with 2-ps resolution. The resultant pulse shape shows ringing typical for superradiance in extended sample. The pulse shape is measured as a function of input power and is compared to the solutions of Maxwell-Bloch equations. The observed superradiance, which is in the low-excitation regime, is found to be closely related to optical precursor behavior. 2012 American Physical Society.