SPECTROPHOTOMETRIC STUDIES OF ULTRA LOW LOSS OPTICAL GLASSES .3. ELLIPSOMETRIC DETERMINATION OF SURFACE REFLECTANCES

The method of measurement of low loss glasses by the comparison of the transmission through two samples of different length requires that the difference in reflection losses between samples be known. It has been shown that polished glass develops a surface layer with optical properties different to the bulk. Ellipsometry is used to assess the surface properties. This paper describes the development of an ellipsometer which has the refinements necessary for such measurements where small absolute ellipticities from low reflectance surfaces are observed. Discussion of the experimental procedure and precautions are included.