| Zugriffsnummer | 33962 |
| Dokumenttyp | Konferenzartikel in Zeitschrift |
| Sprache | Englisch |
| Titel | Utilisation of coincidence criteria in absolute length measurements by optical interferometry in a vacuum and in air |
| Autor(in); Institution |
Schödel, René; 5.4, Interferometrie an Maßverkörperungen, PTB-Braunschweig
|
| Quelle/Jahr | Measurement Science and Technology: 26 (2015), 8, 084007-1 - 084007-9 |
| ISSN | 0957-0233 |
| DOI | |
| URL | |
| Verlag | Bristol: IOP |
| Konferenzangaben | 2nd MacroScale at Bundesamt für Eich- und Vermessungswesen: Recent developments in traceable dimensional measurements, Vienna, 28-30, October, 2014, Austria |
| Klassifikationscode | PACS: 06.30.Bp ; PACS: 42.72.-g ; PACS: 07.60.Ly ; PACS: 06.20.fa ; PACS: 07.60.Hv |
| Freie Schlagworte | precision interferometry ; absolute length measurement ; air refractive index ; refractometer |
| Zusammenfassung | Traceability of length measurements to the international system of units (SI) can be realized by using optical interferometry making use of well-known frequencies of monochromatic light sources mentioned in the Mise en Pratique for the realization of the metre. At some national metrology institutes, such as Physikalisch-Technische Bundesanstalt (PTB) in Germany, the absolute length of prismatic bodies (e.g. gauge blocks) is realized by so-called gauge-block interference comparators. At PTB, a number of such imaging phase-stepping interference comparators exist, including specialized vacuum interference comparators, each equipped with three highly stabilized laser light sources. The length of a material measure is expressed as a multiple of each wavelength. The large number of integer interference orders can be extracted by the method of exact fractions in which the coincidence of the lengths resulting from the different wavelengths is utilized as a criterion. The unambiguous extraction of the integer interference orders is an essential prerequisite for correct length measurements. This paper critically discusses coincidence criteria and their validity for three modes of absolute length measurements: 1) measurements under vacuum in which the wavelengths can be identified with the vacuum wavelengths, 2) measurements under air in which the air refractive index is obtained from environmental parameters using an empirical equation, and 3) measurements under air in which the air refractive index is obtained interferometrically by utilizing a vacuum cell placed along the measurement pathway. For case 3), which corresponds to PTB's Kösters-Comparator for long gauge blocks, the unambiguous determination of integer interference orders related to the air refractive index could be improved by about a factor of ten when an 'overall dispersion value,' suggested in this paper, is used as coincidence criterion. |
