Challenges on double ended gauge block interferometry unveiled by the study of a prototype at PTB

Abstract

Gauge blocks (GBs) are very important material standards that provide industry with reliable and traceable standards of length. At the highest accuracy level, the measurement of GBs must be performed by interferometry. The double ended interferometer (DEI) offers an alternative to obtain traceable measurements of the absolute length of GB shaped objects without the need for a platen to be wrung to one of the faces. In spite of this general advantage, there is no reliable DEI system being used at any National Metrology Institute (NMI). PTB, as the NMI of Germany, is developing a dedicated DEI which will be situated in a temperature-stabilized vacuum chamber. This paper describes a preliminary prototype DEI that was built firstly to study the measurement principle, and secondly to learn about the challenges and limitations to be taken into consideration for the final design. A comparison of results from the DEI measurements and those from PTB's existing single ended GB interferometers (SEI) indicates that the present prototype is a basis for the final version.

Dimensional artefacts to achieve metrological traceability in advanced manufacturing

“…Several wringing-free double-ended set ups exploiting the two measuring faces directly as interferometric mirrors have been reported (e.g. [1], [180], [182], [277]). However, the wringing thickness is not included in these measurements while it is in the ISO 3650 definition, and a correction is needed.…”

Length Traceability Using Interferometry

“…The light is reflected from two reference mirrors (RM1, RM2) to create interference patterns from both ends of the gauge block (GB), as well as combinations of the total cavity length with the gauge block length, from which the absolute gauge block length can be derived. Abdelaty [29] has shown for a similar set-up that there are challenges, especially as the phase correction has to be applied twice and its uncertainty contributes accordingly, and additional mirrors and beam splitters of high quality are needed. Another approach was taken by Winarno et al [30], who combine a double-sided interferometer in a triangle configuration with a displacement measurement that can be carried out remotely.…”

Proposed extension of double-ended gauge block interferometers for measuring spheres

“…In order to ensure the traceability of the length to the SI definition, gauge blocks play an important role. Over the past two decades, more and more double-ended gauge block interferometers (DEI) have been developed [2][3][4][5][6]. They offer an alternative to get traceable measurements of the absolute * Author to whom any correspondence should be addressed.…”