Femtosecond time-resolved dielectric function measurements by dual-angle reflectometry

We present a technique to measure the dielectric function of a material with femtosecond time resolution over a broad photon energy range. The absolute reflectivity is measured at two angles of incidence, and epsilon(omega) is calculated by numerical inversion of Fresnel-like formulas. Using white-light generation, the single-color probe is broadened from the near IR to the near UV, but femtosecond time resolution is maintained. Calibration of the apparatus and error analysis are discussed. Finally, measurements of isotropic, thin film, and uniaxial materials are presented and compared to reflectivity-only studies to illustrate the merit of the technique. (C) 2003 American Institute of Physics.