Laser induced dynamic spectral weight transfer in La_0.7Ca_0.3MnO₃

We report on optical pump-probe measurements at 1.5 eV and 3 eV on the colossal magnetoresistance material La_0.7Ca_0.3MnO₃. The material response is determined in the femtosecond to the nanosecond temporal regimes. By analyzing the absorption and refractive dynamics within the Kramers-Kronig transformations we demonstrate dynamic spectral weight transfer from the intraband Drude component to the interband transitions. This spectral transfer and its strongly temperature dependent dynamics are discussed in the framework of photoinduced demagnetization due to the exchange of energy and thermal equilibration among the electronic, lattice and spin systems. This effect is observed in other manganites with different transition temperatures. The measured dynamics are found to be insensitive to the excitation photon energy.