Extended range metrology: an age old problem

Interferometric metrology is well established for both single point and full field measurements. However, absolute techniques for long range measurements, spanning 100's to 10,000's of fringe orders whilst maintaining sub-fringe resolution have been reported with widely varying levels of performance. In this paper, techniques for long range multi-wavelength interferometry are reviewed with respect to applications of classical interferometry and fringe projection profilometry. Whilst hierarchical geometric series methods provide a potential solution it is shown that significantly greater freedom in wavelength selection is obtained by applying excess fraction principles and a new predictive model for this technique is discussed.