Abstract

Three independent techniques for the measurement of the optical constants of a single dielectric layer on a glass substrate are compared for Al₂O₃, ZrO₂, TiO₂, NdF₃, and LaF₃. The first technique, inspired by Abeles,¹ compares the reflections from coated and uncoated surfaces in both polarizations until a balance is obtained. This yields n values at a single visible wavelength with an accuracy of ±0.005. This method is useful over a wide range of film thicknesses. The envelope method employs reflectance and transmittance data over a wide wavelength range. An inhomogeneous model derives the optical constants, the thickness, and the inhomogeneity of the dielectric layer as a function of wavelength, with a precision in n of just under ±0.02 absolute and in k from ±2.5 × 10⁻⁴ at short to ±5 × 10⁻⁴ at long wavelengths.² If the index and thickness of the film are large enough to allow waveguiding, the measured coupling angle yields the effective index N incorporating the actual index and thickness and provides n values with an accuracy of ±0.001. Although the three techniques have their differences, they produce comparable results for n, k, thickness, and degree of inhomogeneity. This comparability provides a checking mechanism for these parameters and allows insights into the deposition process.

© 1986 Optical Society of America