Photoelastic Constants of Vitreous Silica and Its Elastic Coefficient of Refractive Index

The photoelastic constants and their dispersion for visible light were determined for two samples of vitreous silica, Corning and Herasil No. 1. The results for the mercury green line, 546 mμ, are quoted here. The photoelastic constants were 4.22×10−13 (d/cm2)−1 (ordinary ray) and 3.56×10−13 (d/cm2)−1 (extraordinary ray). From the ratio of Poisson's ratio to Young's modulus 0.216×10−12 (d/cm2)−1 and Young's modulus 0.76×1012 (d/cm2), which were also determined, there were calculated the pressure coefficient of refractive index 0.909×10−12 (d/cm2)−1 and the elasticity volume coefficient of refractive index V dN/dV=0.34. Comparison of these results with those reported for other glasses indicates that the oxygen ions of vitreous silica are more deformable then the oxygen ions of other siliceous glasses. In vitreous silica about ⅓ of the volume change accompanying an elastic dilatation arises from the dilatation of the oxygen ions. A comparison is also made with the results reported for corresponding thermall...