FEMTOSECOND RESPONSE OF OPTICAL-CONSTANTS DUE TO CHARGE-TRANSFER EXCITATIONS IN ND2CUO4

We have performed femtosecond reflectivity Delta R/R and transmissivit y Delta T/T measurements in Nd2CuO4 thin film at 80 and 300 K. We have derived time variations of Delta epsilon' and Delta epsilon '' from t ransient data of Delta R/R and Delta T/T. Assuming a Lorentz oscillato r model consisting of three oscillators, we obtain spectra of the real part epsilon' and imaginary part epsilon '' of dielectric function fr om the measured reflectivity and absorption spectra in the visible-uv region. The absorption bands in the visible region are assigned to in- plane charge-transfer (CT) excitations, and relaxation times of CT exc itations are found to be 0.6 and 1.0 ps. (C) 1998 Elsevier Science Ltd . All rights reserved.