Ellipsometric study of polished glass surfaces

Abstract

The refractive index n f and thickness d f of the “polish layer” on the surface of various kinds of glass polished under standard conditions were determined by ellipsometry. The method of ellipsometry employed was based on the measurement of the principal angle of incidence and the ellipticity of the light reflected at this angle. It was found that n f < n b ( n b is the bulk index of glass) with glasses which are susceptible to weathering, and n f > n b with chemically durable glasses such as silica glass, Vycor and Pyrex. It is presumed that there are two leading factors which affect the value of n f: One is the very high local pressures exerted on the glass surface by particles of the polishing agent, which may increase n f through densification of glass, and the other is the leaching action of the water-based slurry, which will decrease n f. The value of n f relative to n b will be determined by the balance between these two factors. These hypotheses have been qualitatively verified by annealing the polish layer, which, if the increase in n f be due to densification, ought to decrease n f, and by leaching the polished surface in the slurry for some period.