  Photoinduced effects in a single crystal of bilayered manganites,
La2-2xSr1+2xMn2O7 (x=0.38), were investigated in a wide range of temperatures
by pump-probe measurement at a photon energy of 1.6eV. In a ferromagnetic
metallic state, significant enhancement of positive rise in differential
reflectivity with a slow relaxing time of hundred picoseconds was observed just
below Tc=127K, indicating that the reflectivity change with the slow relaxation
time constant is induced by laser heating. We have also observed an
unconventional fast relaxing component that has a time constant of the order of
ten picoseconds. This fast relaxing component, whose absolute value has an
asymmetric peak at Tc, is presumably due to short-range correlation of
Jahn-Teller distortion.
