  Using spectral hole-burning-based ultraslow group velocity in a dilute solid
medium, we report enhanced photon echo efficiency three orders of magnitude
higher than that in a nonslow light regime. The enhancement is due to
exponentially increased absorption of an optical data pulse owing to the
enhanced photon-atom interaction in an ultraslow light regime, whereas echo
reabsorption is negligibly small due to group-velocity dependent population
depletion.
