Modern space optical remote sensors use many off-axis aspheric surfaces to improve performance and increase the field of view. The geometric parameters of the off-axis aspheric surface include its vertex radius of curvature and aspheric surface coefficients, which have an important influence on the performance of the remote sensor. With the continuous improvement of remote sensor performance indicators, the aspheric surface diameter and vertex radius of curvature continue to increase, and the tolerances are becoming more and more strict. Traditional geometric parameter measurement methods such as three-coordinates and compensator control cannot meet the requirements. In order to achieve high-precision measurement of geometric parameters of aspheric surfaces, a laser tracker cooperated with CGH to measure geometric parameters was researched. The structure of CGH is simple, and the optical reference is easy to accurately establish, convert and reproduce. The tracker has high measurement accuracy and wide range. Its software can model and calculate angle relationships, and can perform spatial measurement and positioning of complex optical paths with folding mirrors. Using the simple structure of CGH and the laser tracker to accurately measure the distance, the aspheric surface detection optical path high-precision positioning (0.01mm) and optical axis reference lead (5") to meet the tolerance requirements of geometric parameters. Through simulation analysis and experimental verification. The calculation accuracy of the vertex curvature radius can reach 0.01%, and the accuracy of the aspheric coefficient can reach 0.0001.
To meet the fast and high precision manufacturing requirements of space optical system, experimental research on rapid processing and testing of a 316mm aperture free-form optical mirror was carried out and current fabricating technologies were optimized. In terms of rapid fabrication, process parameters of ultrasonic vibration-assisted grinding were improved firstly, and the method of expending and removing of the optical surface edge based on robot polishing is adopted. In terms of testing, applying scanning white light interferometry (SWLI) technology based on CMM machine to test the surface figure can improve the detection efficiency by more than 10 times when the density of the test point is 100 times higher than point contact CMM testing mode. Finally, the result shows that The accuracy of full-aperture inner surface of free-form surface is better than that of λ/55 RMS. The total time of effective machining and testing of free-form surface is less than 360hrs. The results show that the Optimized process has the advantages of efficiency compared with traditional process and can also achieve high precision at the same time.
A computer-generated hologram(CGH) was designed and produced for precisely testing the off-axis aspheric mirror with departure of 1200um in a three mirror astigmatism optical system.To solve the problem of selection of incident light position in CGH design Depended on engineering experience was likely to increase spatial frequency of CGH which reduced testing accuracy of aspheric mirror. A CGH design method was proposed based on quantitative calculation of incident light position which reduced the reliance on experience. The testing result by CGH was compared with that of non-contact profile testing method when the off-axis aspheric mirror surface was polished to 0.05λ(RMS).Two testing results show a good agreement. By CGH testing method,the surface error is 0.016λ RMS now.
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