The result of interferometric measurement of gauge block length has to be corrected for difference between phase shifts at reflection at gauge block and platen. The aim of the project is collection/exchange of information about the phase shift measurement and its uncertainty. In addition to stack method and wringing to glass platen we will investigate the possibility to derive phase correction from roughness and reflectivity measurements. The comparison of concontact (double sided) interferometric measurement with standard (wringing) method will be performed and evaluated for gauges of different materials and surface quality (at least steel and ceramics).
Final Report 2018-10-05
The phase corrections were determined by stack method by each institute for all combinations of gauge and platen material, in addition with integrating sphere and slave block methods in VTT MIKES and with GUM surface roughness WM method in GUM. CMI has measured the lengths with both standard and noncontact (double ended) interferometers. CMI has developed setup and method for estimation of the correction by Newton’s rings phase evaluation; it was delayed due to initial problems with repeatability of phase correction measurement of steel, later solved by precise estimation of focus, ring phase interpolation, intensity variation correction and proper selection of image area used for processing. CMI has measured also the surface roughness by AFM.
The results were exchanged by participating institutes in 2017 and processed, the resulting (corrected) central lengths agree within ±15 nm for all 12 gauge blocks. It was shown that the optical distance estimated by the Newton’s rings method could be directly used as correction for non-contact measurement of both steel and ceramics gauge blocks with uncertainty similar to that reached by standard (ISO 3650) interferometric method. The Newton’s rings method is useful especially in cases where the stack method cannot be applied – e.g. for long gauge blocks and individual gauge block (not delivered in a set from the same manufacturing batch).
The results were presented at Macroscale 2017 conference in Espoo, Finland (#15_2017)
Phase and roughness correction for interferometric measurement of gauge blocks).
The remaining problem - strange values of extrapolation to zero roughness - was solved in 2018 (original AFM Ra values were wrongly high by 0 nm … 4 nm due to the influence of residual contaminants/dust). The manuscript "Linking the optical and the mechanical measurements of dimension by a Newton's rings method" by Petr Balling, Zbigniew Ramotowski, Robert Szumski, Antti Lassila, Petr Křen and Pavel Mašika was written and submitted to Metrologia in October 2018.
The international cooperation within EURAMET helped us to check existing measurement and correction methods, to develop a new one and to validate it.
The Newton's rings method may contribute to improvement of uncertainty of new optical (non-contact) methods in dimensional measurements and bring exploitation, spread and increased frequency of use of these methods, because it is substantially easier and faster than alternative stack method or roughness and phase change measurement.
Progress Report 2014-11-30
Project started in May 2013. GUM provided three sets of four stable gauges with known history, from different materials and of different surface texture with lengths (2..10) mm. GUM also provided two small platens (ceramics and glass), each participant will use its own steel platen. The phase corrections will be determined by stack method by each institute for all combinations of gauge and platen material. In addition, GUM will measure the surface roughness and flatness of gauges and platens, CMI and MIKES will measure lengths with both standard and noncontact (double ended) interferometers. CMI is developing setup and method for estimation of the correction by Newton ring method; it is delayed due to problems with repeatability of phase correction measurement of steel.
Measurements were partly done by GUM and CMI in 2013 and 2014.
In 2014 MIKES has completed measurement with wringing to different platens, measurements for surface roughness with integrating sphere, measurement for phase change correction by slave block method for selected GBs, measurement for phase change correction by cross method for selected GBs and measurement of all GBs with our double ended set-up.