IR ELLIPSOMETRY OF THE HIGHLY ANISOTROPIC MATERIALS ALPHA-SIO2 AND ALPHA-AL2O3

We have performed ellipsometric investigations of uniaxial crystals of alpha-SiO2 and alpha-Al2O3 in the wavenumber range 430-1350 cm-1. The spectra were taken at multiple angles of incidence for several high symmetry orientations of the optical axis. The ellipsometer attached to a Fourier transform spectrometer was operated with and without a phase-shifting prism. The very strong anisotropy due to different energies of the lattice vibrations along the optical axis and perpendicular to it is recovered from the measured spectra of psi and DELTA by numerical inversion of the Fresnel formulae. The spectral structures of the transverse resonances and their longitudinal counterparts are compared with the results of normal-incidence reflectance and Raman scattering.