Birefringence due to laminar inhomogeneities in commercial flat glass

Abstract

Sensitive measurements of birefringence across the thickness of commercial flat glass show an overall negative mean value, as well as fluctuations from point to point. The observed mean is attributed to 'mode birefringence' due to propagation of the light by dielectric waveguide modes in layers of slightly above average refractive index considerably thicker than the wavelength. The results are consistent with index variations of around 0.001 in layers up to 100 mu m thick, due to variations of 0.1-0.2% in the CaO content.