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Continuous phase plate (CPP) is an important diffractive optical element, which is widely used in high power laser devices. The continuous phase plate with a small aperture period of 4 mm is processed by the atmospheric pressure plasma polishing (APPP). Through the study of the reaction mechanism, it is found that the removal volume has a non-linear relationship with the dwell time, which will lead to machining errors. Based on this, a dwell time compensation method is proposed, and the machining program is generated according to this relationship. A 70mm × 70mm × 20mm continuous phase plate was fabricated by using the processing program generated by this method. The processing time was 4.5h, and the surface residual converged to 57.188nm RMS. The experimental results show that the method can effectively calculate the removal function under different dwell time, and significantly improve the machining accuracy.

For the high efficient and high accuracy convergence of surface figure of a large aperture workpiece, the continuous polishing technology was investigated. As the convergence efficiency of surface figure of the workpiece was effected directly by the flatness of pitch lap in a continuous polisher, a high precision measurement equipment with repeatability accuracy of ±1 μm was designed and developed for measuring the flatness of the pitch lap. The change rules and correlation between the flatness of pitch lap and the PV value of surface figure for the workpiece were analyzed during continuous polishing, and relationship between the flatness data and the surface figure of the workpiece was obtained based on the measured data. The experiments indicate that when the diference between flatness and surface curve are larger, the shape of the workpiece is rapidly converged to about 1λ, meanwhile the polishing process transits from a rough polishing to a fine polishing. The high precision measurement equipment proposed by the paper implements precise measurement of the flatness for a large wet pitch lap and provides an important technical support for deterministic continuous polishing. ? 2016, Science Press. All right reserved.

Uniform Ni-P-nano Al2O3 eletroless plating layer was produced on medium carbon steel, and scanned by high power continuous wave (CW) CO2 laser beam. Optical microscope (OM) and scanning electron microscopy (SEM) were used to observe the morphologies of the coating. X-ray diffraction (XRD) and X-ray energy dispersive spectroscopy (EDS) were employed to analyze the phase transformation and element compositions of the coating. The microhardness and abrasive resistance before and after laser processing were checked respectively. The whole coating was divided into four regions from surface to inner as laser strengthened region, transition zone, heat affected zone (HAZ) and substrate. The strengthened coating had good performances such as smooth surface, uniform components and refined microstructures. The phases in strengthened layer obviously changed from amorphous to crystalline and the main phase was Ni3P with some non-equilibrium phases. The reinforced particles, Al2O3, were homogeneously dispersed in grain boundary, which could improve the properties. The microhardness of strengthened region was about 3 times of substrate, and the abrasive resistance of which was also increased owing to the Al2O3 particles.Uniform Ni-P-nano Al2O3 eletroless plating layer was produced on medium carbon steel, and scanned by high power continuous wave (CW) CO2 laser beam. Optical microscope (OM) and scanning electron microscopy (SEM) were used to observe the morphologies of the coating. X-ray diffraction (XRD) and X-ray energy dispersive spectroscopy (EDS) were employed to analyze the phase transformation and element compositions of the coating. The microhardness and abrasive resistance before and after laser processing were checked respectively. The whole coating was divided into four regions from surface to inner as laser strengthened region, transition zone, heat affected zone (HAZ) and substrate. The strengthened coating had good performances such as smooth surface, uniform components and refined microstructures. The phases in strengthened layer obviously changed from amorphous to crystalline and the main phase was Ni3P with some non-equilibrium phases. The reinforced particles, Al2O3, were homogeneously dispersed in grain...