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Diamond turning aspheric projector mirrors

Nowadays ultra precision machining of single-point diamond turning has played an important role in manufacturing high-precision optical components where surface finish is critical. This paper describes how diamond turning technology was applied to fabricate two tight-tolerance, high accuracy aspheric mirrors for a big-screen high-resolution television projection system. The system consists of two mirrors, a primary and a secondary mirror. Both mirrors have off axis rotational aspheric form. In order to get a good finish, the mirror surface was nickel plated and then diamond turned. Post polish was applied to remove diamond turning grooves and to improve the surface quality. As the off-axis aspheric surface could not be measured by conventional profile meter, a white interferometer was used to measure the off axis aspheric form. The measurement results were compared with that of the design CAD model. The form deviation was less than 3 um. The optical performance of the mirrors was tested in an optical lab. The result was very satisfactory. As the diamond turned prototype mirrors worked so wonderfully with the system, mass production of the mirrors by plastic injection is on the way to bring the new products to the market.