A new optical flatness reference measurement system

A new optical deflectometric flatness reference measurement system will be built up at the PTB. This system offers the possibility of flatness measurements of large samples with diameter up to 700 mm. A measurement uncertainty in the sub-nanometer range for a confidence interval of 95% is aimed at. Deflectometric and difference deflectometric measurement methods will be implemented for horizontal as well as vertical specimens. The high accurate angle measurements will be accomplished by an autocollimator. As straightness reference the straight propagation of light is used. In contrast to conventional interferometry, no external reference surface is necessary. The difference deflectometry, which was developed at PTB, has the advantage - in comparison to deflectometry - that the measurement uncertainty scales almost linearly with the length of the specimen. We present in detail the mechanical and the optical setup. Further on we discuss the main input quantities to the measurement uncertainty by modeling of the system and we show exemplarily an uncertainty budget.