High-power laser devices have stringent requirements for the surface accuracy of optical elements. Continuous polishing is an effective technique for polishing high-precision optical elements. To overcome the problem of poor real-time capability and low accuracy in traditional surface shape monitoring and controlling methods used in continuous polishing, an online monitoring device is developed to monitor the surface shape of the polishing pad. The experimental results of the online measurement are highly consistent with the offline results obtained using an interferometer. The correctness and feasibility of the online monitoring scheme are well validated. Based on the online monitoring device for the surface shape of the polishing pad, we propose a method of automatic control for the surface shape of the polishing pad. This method maintains the flatness of the polishing pad to 0.05λ (λ = 632.8 nm), peak to valley, as measured on a 100-mm monitoring element through computer control.
In conventional continuous polishing process, the surface shape of work-piece was measured by an optical plane template after being placed in such environment with constant temperature for 1 to 2 hours. During this period, uncertain influence may occur on the polishing pad due to the change of system state. Meanwhile, the regular off-line testing may cause re-processing. In this paper, a new method about on-line monitoring surface shape of optical elements is proposed by the theory of run sphere, and the change in curvature radius of the work-piece which lead to its radial tilt angle change. The change in work-piece surface shape indirectly obtain by the correction plate small angle with respect to the horizontal, and the angle were detected on line by the high-precision goniometer with the resolution 0.04 ''. According to theoretical calculations, the diameter of 200mm precision work-piece PV value up to 0.02λ (λ = 632.8nm). The fused quartz glass was measured by above method. The test results showed that the surface accuracy and processing efficiency were significantly promoted, and also improving the controllability of surface shape of work-piece based on this method.