ANISOTROPY OF OPTICAL CONSTANTS AND ELECTRON ENERGY LOSS

Dispersion relations for the energy loss rate are derived for anisotropic materials; they are a nontrivial extension of the usual Kramers-Kronig expression. It is shown for the case of uniaxial crystals that these formulae allow a determination of the longitudinal dielectric tensor from electron energy-loss experiments. The connection between the dielectric tensor so obtained and the optical constants is examined and their equivalence is established in the long-wavelength limit. © 1969 Società Italiana di Fisica.