  We show evidence that the competition between the antiferromagetic metallic
phase and the charge- and orbital-ordered insulating phase at the reentrant
phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using
ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller
superlattice reflection, which indicates the formation of the charge and
orbital order, was measured at different laser fluences. The laser-induced
enhancement and reduction the Jahn-Teller reflection intensity shows a reversal
of sign between earlier (~10 ns) and later (~150 ns) time delays during the
relaxation after photo excitation. This effect is consistent with a scenario
whereby the laser excitation modulates the local competition between the
metallic and the insulating phases.
