Elimination of the imprinting effect of the lightweight aspheric polished by CCAL technology using immersed inflation

In order to reduce the quality of overall optical system and improve the capability of correcting aberration, amending image quality and expanding the field of view. The optical components of optical systems are trending to the lightweight aspheric with larger radius to thickness ratio. For improving the processing efficiently and restraining the mid-high frequency error, Computer Control Active Lap (CCAL) technology has become a significant method for processing. However, when the surface accuracy RMS of lightweight mirrors is lower than λ / 40 (λ = 632.8nm ), the lightweight mirror surface will appear “imprinting effect” stripes caused by Active Lap, and this phenomena has become the barriers for high-precision processing and the development of lightweight mirrors. In this paper, based on the Finite Element Analysis (FEA) software, taking an innovative way that applies reverse air to the internal structure of lightweight mirrors to resist the elastic deflection derived from the lap pressure and self-weight. And, comparing two methods: cavity inflation and immersed inflation, simulation results show that the immersion inflation method not only can eliminate the “imprinting effect, but also the surface accuracy of mirrors is much better than that only caused by selfweight during polishing process.