Thermal stress limitations to laser fire polishing of glasses

Abstract

The process of laser fire polishing of optical glasses is shown to work very well for materials with small coefficients of thermal expansion. The surfaces of other glasses crack during laser fire polishing or during cool down from an elevated preheat temperature. An analytical model is described and is used to show that, in materials which cannot be laser fire-polished, the thermal-gradient stress resulting from differential expansion exceeds the yield stress. Successful laser fire polishing of fused quartz and Pyrex glasses is reported.