To solve the problem of machining accuracy of a convex blazed grating for an Offner imaging spectrometer by diamond turning limiting the imaging quality of the optical system, analyze the effect of Poisson burr on the diffraction efficiency of convex blazed grating, investigate the effect of the layout of blazed grating on the convex surface on the machining accuracy, and compare the performance of cutting convex gratings with microcrystalline aluminum RSA6061 and RSA6061 + chemically plated NiP for two workpiece materials. Turning with a 4-axis ultra-precision machining system yielded a convex blazed grating with a substrate radius of curvature R=41.104mm, substrate diameter of 14mm, the grating density of 53.97 line/mm, and blaze angle of about 3.8°. Cutting experiments show that RSA6061+ chemically plated NiP material is better for convex grating processing; the blaze angle error is better with the equal-along-projection layout than with the equal-along-arc layout; Poisson burr height is about 0.3μm; and the average roughness of the final grating blaze surface is less than 5nm to meet the processing quality requirements.
The physical characteristics of silicon carbide materials, such as brittle texture and high hardness, make it very difficult to form complex structures. Additive manufacturing can realize the direct molding of complex structure silicon carbide mirrors, improve processing efficiency, and reduce processing costs. In this paper, an additive silicon carbide mirror substrate is processed by the combined process of grinding, lapping, and polishing with a small grinding head. After obtaining a certain surface shape accuracy, the surface was modified to obtain a silicon modified layer with a thickness of 10 μm. After two times of magnetorheological modification of the modified layer, the surface shape converged to 17.313nm RMS. After a conformal smoothing, the surface quality was 1.109nm Ra, which verified the machinability of the additively manufactured silicon carbide mirror.
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