Manufactureing of 720mm SiC Aspherical Mirror

3.Rough polishing: Rough polishing further improves the surface roughness and surface accuracy of the larger aperture SiC aspherical mirrors. CNC small grinding heads are still used for rough polishing, and the latter stage MRF-Magnetorheological Finishing is also involved. After rough polishing, the mirror surface enters the interference metrology stage, and can enter the Si coating stage after the surface accuracy RMS value is better than 1/10 λ.

4.Si Coating: The mirror blank material of a large aperture SiC aspherical mirror often uses reaction-sintered SiC material, which has slightly lower density compared to pressure-sintered SiC material. In order to improve the reflectivity of the larger aperture SiC aspherical mirror, a layer of Si is plated on the mirror surface to improve the surface density.

5.Fine polishing: After modification, the larger aperture SiC aspherical mirror enters the fine polishing stage. CNC small grinding heads, Stress Lap Polishing, and MRF-Magnetorheological Finishing are often used in the initial stage of fine polishing to remove the relatively loose layer on the modified surface. Later, CNC small grinding heads, together with Ion Beam Figuring, are used to refine the surface accuracy to the design requirements. At present, the surface accuracy of larger aperture SiC aspherical mirrors can be processed to a full-diameter RMS value better than 1/60 λ or even better.

After several years of technical accumulation, MG-Optics currently has the ability to develop the entire process of large-aperture SiC aspherical mirror. A set of 720mm diameter large-aperture SiC aspherical mirror has been completed with a final surface accuracy full-diameter RMS value better than 1/60 λ.