  We present an absolute extraction method of optical constants of metal from
the measured reflection electron energy loss (REELS) spectra by using the
recently developed reverse Monte Carlo (RMC) technique. The method is based on
a direct physical modeling of electron elastic and electron inelastic
scattering near the surface region where the surface excitation becomes
important to fully describe the spectrum loss feature intensity in relative to
the elastic peak intensity. An optimization procedure of oscillator parameters
appeared in the energy loss function (ELF) for describing electron inelastic
scattering due to the bulk- and surface-excitations was performed with the
simulated annealing method by a successive comparison between the measured and
Monte Carlo simulated REELS spectra. The ELF and corresponding optical
constants of Fe were obtained from the REELS spectra measured at incident
energies of 1000, 2000 and 3000 eV. The validity of the present optical data
has been verified with the f- and ps-sum rules showing the accuracy and
applicability of the present approach. Our data are also compared with previous
optical data from other sources.
