The Physikalisch-Technische Bundesanstalt (PTB, the National Metrology Institute of Germany) reported that it has developed standards for aspheric optics. The standards are intended to improve the calibration of aspheric and freeform surface measuring devices.
Aspheres are optics whose shape deviates significantly from the spherical shape. They are essential components of many modern imaging systems. In contrast to spherical optics, aspheres' traceable measurement, with uncertainties in the range of a few tens of nanometers, represents a major challenge. Tactile measuring methods, such as microcoordinate measuring machines (µCMM) and optical measuring methods, are currently used to measure aspheres and freeform surfaces.
The newly introduced asphere standards’ shape properties can be traced back using established measuring technology, such as μCMMs.
An exaggerated representation of a multiradius test body, the first of multiple market-ready standards recently introduced by Germany’s Physikalisch-Technische Bundesanstalt. Courtesy of PTB.
The first of these standards, a patented multiradius test body, is expected to be commercially available in spring. It combines spherical segments of various radii. The radii of the individual spherical sections, and the small but unavoidable deviations from the perfect spherical shape (sphericity), can be measured, for example, by using Fizeau interferometers. The shape properties that are determined in this way then serve as a reference for devices that measure nonspherical optical surfaces.
A company that is active in the field of ultraprecision technology — a producer of metal optics, among other products — has secured the technology transfer for the production of the asphere standards, becoming the licensee, according to PTB.
The development of the standards is the result of two research projects funded by the European Association of National Metrology Institutes.