Low thermal expansion materials for high precision measurement equipment

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.