Measurement of thermally induced changes in the refractive index of glass caused by laser processing

The effects of CO2 laser heating of pure fused silica are investigated. Studies show that the laser heating process causes a small volume of glass to be left in an altered microstructural state. To measure the refractive index of this altered region, a process was developed to create a thin film of altered glass. Samples were measured with a prism coupler, and a theoretical model was developed to predict the intensity values collected during the measurement. A least-squares routine was used to determine the refractive index that results in the best fit between the experimental and predicted intensity data. The refractive index in the altered glass was found to increase by approximately 0.07%.