Advances in interferometric length measurements of short gauge blocks

Abstract

A system of interferometric length measurements has been realized that supports wringing and phase change errors of 1 nm. In this system, special reference blocks allowing reproducible wringing are used to find the relation between optical and mechanical lengths. The optical length of a reference block is found by the double-sided method on a quartz plate. The mechanical length is found by the combination of the reproducible wringing and slave-block techniques. A comparison of these two length values gives the phase change at the optical reflection, which is then used to find the mechanical length from the double-sided measurement results of a block of arbitrary length (up to 100 nm). The proposed system makes it possible to measure the phase change difference between the blocks with sub-nanometre accuracy. The system can be used for the practical realization of an alternative definition of the length of a material artefact, based on the perpendicular distance between its mechanical surfaces. Precise measurements of the excessive thickness of the wringing film, which is included in the present definition of the length of a block, are demonstrated. Standard single-sided measurements on quartz are shown to have some additional uncertainty relative to standard measurements on steel plates.

Scientific basis for traceable dimensional measurements in a nanometer range: methods and concepts

“…This type of the error (which is about 10 nm for the wring 3 in Fig 9) is to be associated with the installation of the artefact in the measuring comparator. Wringing number p AGP An important improvement in the accuracy of the length measurements has been achieved after discovery of the possibility of highly reproducible wringing and the development of the new parallax-free methods in optical length measurements [1][2][3][4]. All ofthem are based on the reproducible wringing technique [5][6][7].…”

“…The improvement in the reproducibility, achieved with the method, is, indeed, fascinating: after the removal of the systematic effect associated with the cleaning procedure, the reproducibility is within 1 A [2]. The well-known "British' slave-block method [9], combined with the reproducible wringing technique, gives a subnanometer uncertainty level for high-quality gauge blocks with the nominal values of a few mm [2,3]. The method can be applied to the measurements of tungsten carbide blocks, which are characterized by much greater deviations from flatness than steel blocks.…”

“…As the bending deformations of the slave-block, which is wrung to the plate, are much smaller than the deformations of a thin measured block [5], the differential measurement result is free from the errors, which are associated with the flatness deviations of the slave-block and the with the curvature of the wave-fronts, related to the optics distortions in the interferometer. If the wringing of the measured block to the slave block is reproducible, then we obtain the mechanical length of a block [2,3]. In case of Fig.…”

“…Here, we are to remind the new length specifying parameters, which have been introduced in [1-3] and will be used below: that is the mechanical length (LM) of a gauge block [2,3] and its optical length [2] (L0). The mechanical length of a block can be defined as the length a block, which is obtained with the combination of the reproducible wringing and the slave-block techniques, and when the wrings to the plate of the same texture as the blocks are performed.…”

“…The report will mainly deal with the new parallax-free methods of length measurements [1][2][3][4]. The calibrated double-sided method, reported here in some detail, extends the approach of parallax-free measurements obtained with the reproducible wringing technique to the general case of an arbitrary gauge block.…”