Optically induced coherence transfer echoes between Zeeman substates

We report on optically induced spin-echo phenomena associated with Zeeman coherences in a sublevel manifold. The experiments on the ground state of sodium show multiple echoes occurring periodically after a double-pulse excitation sequence in an inhomogeneous magnetic field. The echo formation mechanism is attributed to a light-shift-induced transfer of sublevel coherence among the nondegenerate substates. This mechanism is verified experimentally, using a modulated excitation scheme with subsequent phase-sensitive detection.