Abstract

We report the observation of coherent two-photon free-induction decay (FID) in a three-level Λ system excited by a low-intensity square-modulated laser pulse. Using electromagnetically induced transparency in an ${}^{85}\mathrm{Rb}$ cold atomic cloud, for what we believe to be the first time, we observe FID signals with coherence time exceeding the relevant atomic excited-state natural lifetime. Because of the on-resonance enhancement, the two-photon FID signal can be observed at the falling edge without using heterodyne means.

© 2010 Optical Society of America

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