The PSD2 index of 3mm ultrathin large aperture optical components is difficult to converge effectively, which is influenced by various factors. In order to solve the problem, the measurement results of the PSD2 index were analyzed in two parts. One part was the results of the PSD2 index after removing the defocus and astigmatism, which we used to evaluate the impact of intermediate frequency errors. The other part was the surface shape PV value of the measurement area, which we used to evaluate the impact of low frequency errors. In the double-side polishing stage, the oscillating smooth polishing technology was used to smooth intermediate frequency errors of the optical surface, which eliminated the fine ripples in the PSD2 processing results. The surface shape local correction technology was used to improve the surface shape PV value of the measurement area. Through the synchronous control of the intermediate frequency and low frequency errors, the PSD2 index control for the whole surface of the optical components was realized. The RMS value of the the PSD2 index was converged from 1.38nm to 0.70nm on average.
With the increasing energy of high power laser devices, the laser-induced damage of optical components, especially fused quartz components, has become one of the core problems in the development of high power laser devices. Studies show that pure fused quartz glass has a high intrinsic damage threshold, but fused quartz glass will inevitably introduce a large number of subsurface damage during the process of grinding and polishing, and these subsurface damage is one of the important factors leading to the decline of laser damage resistance of optical components. It is of great significance to study the subsurface damage of solid abrasive for improving the damage resistance threshold of optical components. In this experiment, 3M's abrasive pad is used as a solid abrasive. The subsurface damage of fine grinding elements are directly observed and analyzed by combining HF pickling and optical microscopy. The results show that various subsurface damage can be detected by optical microscopy after HF pickling. Profilometer is used to measure the surface roughness of the sample, the comparative analysis of the subsurface damage of the fine grinding elements shows that the elements with solid abrasive lapping have smaller roughness when the abrasive size is the same, which has a shallower depth of subsurface damage layer correspondingly.
For the high demand of large aperture optical element, the regular trajectory errors in machining marks of double-side polishing need to be determinately controlled. The mechanism and control method of the regular trajectory errors in machining marks were deeply studied. The process was simulated and compared with the experiment. The method of active translation and pendulum motion and polishing plate correction were proposed, proved to be efficacious on eliminating the regular machining marks by the groove of the polishing pad and local surface figure errors of the polishing plate. The method of dynamic loading and motion combination was adopted, retaining the independence of the original fast convergence process on surface figure. For the optical element with 430mm×430mm×10mm, the surface figure was controlled below 1λ(PV, λ=632.8nm). Meanwhile, the regular machining marks repeatedly produced were eliminated, which provided the essential condition for the intermediate frequency index in the rear stage, small tool precision polishing, and the high efficiency and stable machining of the optical element in the index system was realized.
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