| Zugriffsnummer | 23891 |
| Dokumenttyp | Konferenzartikel |
| Sprache | Englisch |
| Titel | Extending the capabilities of the sphere interferometer of PTB by a stitching procedure |
| Autor(in); Institution |
Bartl, Guido; 5.4, Interferometrie an Maßverkörperungen, PTB-Braunschweig
Nicolaus, Arnold; 5.4, Interferometrie an Maßverkörperungen, PTB-Braunschweig
|
| Quelle/Jahr | Fringe 2009 : the 6th International Workshop on Advanced Optical Metrology:(2009), 354 - 357 |
| Herausgeber(in) |
Osten, Wolfgang
|
| ISBN | 978-3-642-03050-5 |
| DOI | |
| Verlag | Berlin [u.a.]: Springer |
| Konferenzangaben | Fringe 2009, Nürtingen, 14-16, September 2009, Deutschland |
| Freie Schlagworte | sphere interferometer ; stitching ; radius topography ; form error |
| Zusammenfassung | The kilogram, SI base unit of mass, is still defined in relation to an artifact. Since this artifact is being suspected to change its mass, a new definition of the kilogram based on a natural constant has been taken into consideration. One option is a precise redetermination of Avogadro’s constant. In the scope of the International Avogadro Project - among other quantities - the volume of a single-crystalline silicon sphere has to be measured. The sphere has a mass of 1 kg and a surface of optical quality with a roundness error of only some ten nanometers. The volume is determined at PTB by measuring the absolute diameter of the sphere with a specially developed Fizeau interferometer with spherical reference faces. The intended measurement uncertainty is below 1 nm. As in principle the sphere interferometer allows only the diameters to be measured, the result is a diameter topography. This means that the measured diameters are located point-symmetric to a mathematical centre of the sphere due to the lack of knowledge of its real position. To determine the real form of the sphere and, therefore, to obtain the radius topography, which is most likely not point-symmetric, it is desirable to evaluate the measured data in a way, that regards the topographic information of both sides of the sphere separately. Stitching approaches for concatenating segments of a topography are known in the field of optics fabrication and wavefront testing. The stitching technique can also be used in the case of the topography of a sphere in order to yield its radius topography or rather its form error if the absolute diameter is unknown. Griesmann et al. combined form and radius-of-curvature measurements to obtain the real form of the sphere under test. Pursuing this idea the stitching algorithm specially developed for the sphere interferometer of PTB makes use of the absolute diameter results combined with the two-sided measurement principle. |
