Using curved hologram to test large-aperture convex surface.

A valid optical system with a computer-generated hologram fabricated on a concave lens surface, for measuring large-aperture convex surface, is demonstrated experimentally. The CGH employed in this system has been constructed using a new technology that combines laser direct writing and lithography. This technology allows precise alignment, superior linear profile and high resolution of the gratings that compose the CGH. The particular characteristics of this new type of CGH could derive higher accuracy, efficiency and lower cost for testing aspherics in comparison to other CGH employed previously by other authors. We have designed and fabricated one system and measured a 110 mm-diameter convex surface of errors 300.6 nm P-V after compensating the alignment errors. It is believed that this kind of system can be used to measure even large aperture convex surface.