Optical free induction decay in cold 85Rb atoms

We have observed optical free induction decay (FID) in cold 85Rb atoms. The shortening of the FID lifetime with increasing optical depth of the trap has been found. This shortening is explained by an anomalous absorption for FID propagating in a homogeneous and resonant sample. Theoretical calculations are consistent with experimental results. The Rabi oscillations of FID amplitude have been observed by increasing the pulse area.