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Recently, a scientific comparison of flatness measuring instruments at European National Metrology Institutes (NMIs) was performed in the framework of EURAMET. The specimen was a well-polished optical surface with a maximum measurement aperture of 150 mm in diameter. Here, we present an evaluation concept, which allows the determination of a mean flatness map taking into account different lateral resolutions of the instruments and different orientations of the specimen during measurement. We found that all measurements are in agreement with the mean flatness map within the uncertainty intervals stated by the participants. The aim of this scientific comparison is to specify an appropriate operation and evaluation procedure for future comparisons.

This paper shows the result of work of the Institute of Micromechanics and Photonics at Warsaw University of Technology and the Length and Angle Division of Central Office of Measures (GUM) [1] in building an automatic multiwavelength interferometric system with extended measurement range for calibration of long (up to 1 m) gauge blocks. The design of a full working setup with environmental condition control and monitoring systems, as well as image analysis software, is presented. For length deviation determination the phase fraction approach is proposed and described. To confirm that the system is capable of calibrating gauge blocks with assumed accuracy, a comparison between the results of 300 mm length gauge block measurement obtained by using other systems from the Central Office of Measures is made. Statistical analysis proved that the system can be used for high precision measurements with assumed standard uncertainty (125 nm for a length of 1 m). Finally the comparison between our results obtained for a long gauge block set (600 mm to 1000 mm long) and previous calibrations made by the Physikalisch-Technische Bundesanstalt (PTB) [2] is shown

This paper describes common efforts of Warsaw University of Technology and Polish Central Office of Measure to build a multiwavelength interferometer with extended measurement range to calibrate long gauge blocks. To achieve this goal modified automatic fringe pattern analysis method based on fringe fraction method is proposed. The setup with special chamber with active temperature control to stabilize environmental conditions has been build. To assure correctness of measure factors like temperature, pressure, humidity and concentration of CO2 are need to be constantly monitored by network of sensors. Summarizing all this efforts we are presenting gauge blocks calibration results with uncertainty analysis.

Several standard and measures laboratories are using typical Koester interferometers (KI) and routine measurement procedures for evaluating the practical length of block gauges. In the paper the modification of KI by introducing laser light source and phase shifting element for automatization of interferogram analysis by temporal phase shifting method are presented. From phase data obtained the flatness, parallelism and length deviation of gauge block are automatically determined. The methodology and software procedures for this process are introduced and the examples of measurement are shown.

Determination of a phase correction is necessary when making interferometric measurements of gauge blocks with an auxiliary platen. The phase correction compensates for the differences in the reflecting properties of the gauge block and the platen surfaces. Different phase corrections are reported for gauge blocks of different manufacturers, made from different materials and with different surface roughness compared to the platen. In this paper, the process of selection of the best surface roughness parameter and the influence of different complex refractive indices of the same type of material are analysed. The new surface roughness parameter based on the difference between the weighted mean of maximum and minimum asperities of 3D surface roughness measured by a modernized Linnik phase shifting interferometer is introduced. The results of comparison of the phase correction values calculated from the difference between the weighted mean values and calculated from stack method measurements are presented and discussed. The complementary method of phase correction measurement based on the cross-wringing method with the use of the modernized phase shifting Kosters interferometer is proposed.

At its meeting in Prague in October 1999, the EUROMET Technical Committee for Length, TC-L, decided upon a supplementary comparison on gauge block measurements, numbered EUROMET.L-S12, with the National Metrology Laboratory Ireland (NML) as the pilot laboratory. NPL, UK, agreed to act as co-pilot and linking laboratory to the corresponding key comparison, EUROMET.L-K1, by making both mechanical comparison and interferometric measurements. The comparison was subsequently registered as EUROMET project 601. This report describes the results of measurements of eight gauge blocks at thirteen European national metrology institutes. This comparison was carried out during the period from April 2001 to September 2002. The primary measurement quantity was the deviation of the central length of the gauge block from its nominal length, as defined in ISO 3650. The central length was determined by mechanical comparison against the laboratory reference gauge blocks using an appropriate mechanical comparator. Where possible, the participants also determined the variation in length across the surface of each gauge by undertaking measurements at five points on the surface of each gauge against the central length of the laboratory reference gauge block. The results obtained show a good overall agreement of measurement results with the calculated mean values. The uncertainties claimed in the CMC tables are broadly in line with those achieved in this supplementary comparison. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).