Index, Thickness and Birefringence of Thin Films by Guided Waves

Abstract

A guided wave technique has been used to measure the refractive index and thickness of a thin film. The film, which contained approximately 90 mol % MgO and 10 mol % SiO2 was produced by coevaporation of the two constituents onto a fused silica substrate. Measurements were performed at three visible wavelengths obtained from an argon-ion laser. From the positions of the mode coupling angles, we have calculated the refractive index and thickness of the film. The film was found to have a large birefringence which is attributed to internal stresses. A signature for the birefringence can be observed in the scattered m-line spectrum of the film, in which the order of the TEo and TMo modes is interchanged as compared to an isotropic film. The optical determination of the film thickness is 1.098 ± 0.003 μm as compared to 1.11 μm measured by a mechanical method. The measured values of refractive index agree well with values calculated on the basis of the Drude model.