High precision optical measurement methods

Two wavelength techniques become very interesting for absolute distance measurement. It has been shown, that a synthetic wavelength can be generated by two shorter ones, leading to techniques for measuring optically rougher surfaces. The theory is based on the assumption that the optical path difference is to be compared with the synthetic wavelength. Therefore optically rougher surfaces can be measured and furthermore the unambigiuty range can be extended. Heterodyne interferometry is a powerful tool for high precision distance measurements and vibration analysis. Double heterodyne techniques lead to improvements with respect to environmental disturbances and to absolute distance measuring procedures. To measure the topography of optically rough surfaces fringe projection, short coherence techniques as well as confoacal methods oblique incidence and 2λ interferometry are possibilities to overcome some of the limitations pointed out. The absolute distance measuring technique can further be combined with a technique for topography measurements