Femtosecond response of optical constants due to charge-transfer excitations in Nd2CuO4

We have performed femtosecond reflectivity Delta R/R and transmissivity 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 transient data of Delta R/R and Delta T/T. Assuming a Lorentz oscillator model consisting of three oscillators, we obtain spectra of the real part epsilon' and imaginary part epsilon " of dielectric function from 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 excitations are found to be 0.6 and 1.0 ps. (C) 1998 Elsevier Science Ltd. All rights reserved.