Radius forward measurement for spherical elements of optical measurement instruments – looking for a licensee

A German national research institute active in metrology has developed a measurement process, which enables the efficient measurements of strong curved spherical segments which are often used in optical measurement equipment. Measurement uncertainties due to thermal expansion of the measurement equipment are reduces by at least factor 2. The method uses an interferometer signal coming from the front onto the spherical surface to be measured. In the center (on the optical axis) a phase value is determined, which is determined down to half a wavelength (typically the wavelength is 632 nm). The number of full wave-packets is not given, but can be determined if the distance R would be known to be < 300 nm (about half the wavelength). However, the information is available with such accuracy, because the radius measurements are known via the DMI at 200 nm (k=2), which is measured from behind, even if temperature influences falsify this information. The measurement of spherical lenses is a cornerstone of optical metrology, but constant improvements in accuracy are still the subject of current R&D. The economic aspect is that a significant improvement in accuracy can be achieved by using existing measuring instruments in a changed usage. The described procedure can be implemented relatively "easy" for measurement system manufacturers by integrating new software. In addition, it is possible to replace the rear DMI interferometer by more cost-effective measuring systems.