BK7 optic surface shape affected by non-uniform temperature distribution during continuous polishing

The continuous polishing process has been extensively used in polishing large optical elements with high precision surface figure. During polishing, the interfacial friction between the rotating optic and lap introduces heat into the optic and results in a non-uniform temperature of the optic. The non-uniform temperature distribution would cause optic deformation and thus has a critical effect on the surface figure, which haven't been addressed till now. In this study, we measured the temperature distribution of the optic with buried temperature sensor. We then model the non-uniform temperature distribution, the results show that the temperature at the edge of the optical element is the lowest, and the temperature on the polished surface is the highest. The maximum temperature difference inside the 430 × 430 × 80 mm³ BK7 optic is about 0.4℃. Under such non-uniform temperature distribution, the thermal deformation of the optical element is 1.7 μm.