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Precise determination of the main refractive indices of biaxial anisotropic coatings is essential for the calculation of their optical performance. Measurements based on wave guiding methods have proved to yield excellent results with these layers. A comprehensive study on coatings with relatively low anisotropy, obliquely deposited under angles of 32 degrees or less, was done before, but coatings of higher structural anisotropy have not been concerned yet. With higher deposition angels, new problems arise because the microstructure deviates more and more from the model, and the column inclination angle has an increasing influence on the mathematical separation of the main refractive indices. In a theoretical study, this effect is shown to limit the precision and reliability of the method. Experimental results on HfO2 thin films, deposited under 0 degrees, 30 degrees, 45 degrees, and 60 degrees, will be given. They were achieved using additional information about the coatings from transmission measurements between crossed polarizers and compared to results from ellipsometric and spectral photometric measurements. All measurements were performed at a wavelength of 632.8 nm.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
