Envelope and waveguide methods : a comparative study of PbF2 and CeO2 birefringent films

Abstract

We have characterized low-birefringence, PbF2 coatings to permit, first, agreement between envelope and prism-coupler waveguide methods under the standard isotropic assumption. In essentially the same measurement conditions, for obliquely deposited (58.30) CeO2 coatings the isotropic model becomes unsustainable. Explicit consideration of the film microstructure is then required for good correlation between thickness results from TE (503 ± 9 nm) and TM (504 ± 10 nm) modes in the waveguide experiment as well as between refractive-index results from envelope (n2 = 1.78 + 0.03) and waveguide (n2 = 1.794 + 0.002) techniques. We considered uniaxial and biaxial models to achieve consistency, and the refractive indices along the principal axes of symmetry were determined.