KEYWORDS: Ions, Ion beams, Ion beam finishing, Mirrors, Sputter deposition, Surface finishing, Calibration, X-ray optics, Optical components, Chemical species
Ion beam figuring(IBF) is commonly used during the process of fine optical fabrication. According to sputtering theory, material removal rate varies with the ion inject angle and the surface curvature. During the process of figuring high gradient aspherical surface, the removal function of ion beam figuring should be calibrated strictly to guarantee the accuracy of the figuring results. In this paper, we describe the influence of ion density distribution and surface curvature on material removal rate. Since the removal function varies from point to point within the ion bombed region for high gradient surface, rectification matrix was proposed to fix the disparity between the practical removal function and flat removal function. Experiments were implemented with high gradient aspherical surface to prove the rectification matrix can fit the variety of the material removal rate effectively.
Ion beam figuring (IBF) is an advanced and deterministic method for optical mirror surface processing. The removal function of IBF varies with the different incident angles of ion beam. Therefore, for the curved surface especially the highly steep one, the Ion Beam Source (IBS) should be equipped with 5-axis machining capability to remove the material along the normal direction of the mirror surface, so as to ensure the stability of the removal function. Based on the 3-RPS parallel mechanism and two dimensional displacement platform, a new type of 5-axis hybrid machine tool for IBF is presented. With the hybrid machine tool, the figuring process of a highly steep fused silica spherical mirror is introduced. The R/# of the mirror is 0.96 and the aperture is 104mm. The figuring result shows that, PV value of the mirror surface error is converged from 121.1nm to32.3nm, and RMS value 23.6nm to 3.4nm.
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