Sub-micron profilometry on macroscopic free-form surfaces

One of the advantages of slope-measuring 3D sensor principles like Phase-measuring deflectometry (PMD) [1] is that one can achieve a tremendous dynamic range in terms of height variation with remarkably little technical effort. A typical PMD sensor setup for the measurement of eyeglass lenses has a local slope uncertainty of about 8 arcsec while being able to measure global tilts of ±20°. This corresponds to a dynamic range of approx. 18,000 : 1. By integrating slope data at a lateral sampling distance of 0.1 mm we get a local height uncertainty of only 4 nm, while still being able to measure objects with a global height range of about 10 mm. This corresponds to a dynamic range of approx. 2,500,000 : 1. This gain is achieved by virtue of numerical integration, which is an operation that emphasizes low-frequency shape information and reduces high-frequency noise.