Low thermal expansion materials for high precision measurement equipment

Abstract The operation and mechanical construction of an instrument which measures the shape of aspheric surfaces with ± 5 nm precision is reported1. The instrument makes use of contacting probes, and it functions on the basis of an optical differential technique. To achieve maximum performance the equipment is built in glass-ceramic (Zerodur) and Invar. Special attention is paid to the selection and machining aspects of these thermally stable materials.