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Study on Aspherical Surface Polishing of Single Crystal Silicon Lens.

1997; Volume: 63; Issue: 9 Linguagem: Inglês

10.2493/jjspe.63.1280

1882-675X

Hirofumi Suzuki, Sunao KODERA, Tomoaki Nakasuji, Tsutomu Ohta, Katsuo SYOJI,

Advanced Surface Polishing Techniques

Aspherical lenses of single crystal silicon (Si) are used for the scope and the camera of infrared wavelength, because the very large refractive index of the material leads to substantial reflection loss. These aspherical lenses of infrared wavelength materials were manufactured by diamond cutting. But the single crystal silicon is a hard and brittle material, it is difficult to obtain a mirror surface without a micro crack when the lens diameter is large. In this case, aspherical polishing has to be applied after diamond cutting in order to generate an aspherical surface most precisely. In this study, a computer controlled polishing system using a small rotating polisher was developed for precision finishing of a large size of aspherical surface after diamond cutting. The characteristics of this polishing system are, as follows: (1) A disk shape of forming polyurethane pad was used as the polishing tool, and its rotating axis was controlled to be always normal at the machining point of the workpiece surface. (2) The polishing load was applied from the normal direction of the machining point and controlled to be constant. In the aspherical polishing tests, spherical surface of diamond turned single crystal silicon (111) was polished to generate an aspherical shape. As a polishing abrasive, colloidal silica was used. As a result, a form accuracy of about 0.2 μm P-V (±0.1 μm) and a surface roughness of less than 0.02 μm Rmax were obtained.