Toward subnanometer uncertainty in interferometric length measurements of short gauge blocks

Abstract

A primary-level comparator, with a reproducibility of 0.2 nm and intended for realization of a Systeme International length unit in the range of 1-100 mm, is reported. High-precision differential measurements of phase change on reflection from blocks and end plates are demonstrated. A set of experiments has been developed to measure systematic error associated with nonideal interferometer optics and deviations from flatness of an auxiliary plate. For specially selected high-grade 6-mm blocks, reproducible wringing has been achieved with a random uncertainty in length measurements of 0.1-0.2 nm. Subnanometer wear-off of the blocks as a result of the cleaning has been detected. Under the conditions of reproducible wringing, the accuracy of the length measurements is evaluated to be in the 2-3-nm range for 6-mm blocks.

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

“…In this case, only the divergence of the beams gives the offset of the measured length value. For our comparator this effect is about -0.7 nm for 100 mm block [6], and the uncertainty of the correction is a small fraction of a nanometer. The resolution of our comparator was measured earlier using a double frequency HP-laser with 2 MHz frequency difference between the orthogonally polarized modes.…”

“…The gauge block interferometer, used in almost all of these studies, is a fringe-pattern analyzing comparator [5,6], similar to the well-known NPL-TESA automatic interferometer. The general view of it is shown in Fig 1 . The interferometer is well thermally isolated, and installed on a massive granite slab.…”

“…To reduce it, we use additional beam expander before the telescopic system ofthe interferometer, that reduces significantly the divergence of the beam inside the comparator (with the corresponding loss of the illumination, naturally). Besides, we are using the special beam matching procedure (Fig.4) ofthe incident light to the optics ofthe interferometer [5,6]. The maximum of the curve corresponds to the matching conditions.…”

“…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]. Its idea is very simple.…”

<title>Interferometric length and roughness measurements with nanometer accuracy level</title>

“…In some papers [3,5], for selected blocks with smaller deviations in flatness, the variability of the wringing film thickness is reported to be about nm (at 95% confidence level). In this paper, we describe a new approach in the interferometric length measurements that is based on the technique of the reproducible wringing [6][7][8][9]. It gives the opportunity to measure the physical length of the material artifact without the excessive wringing film thickness and results in the accuracy of the phase change measurements at the optical reflection from surface of the material standard of better than I nm.…”