Precise interferometric length and phase-change measurement of gauge blocks based on reproducible wringing

A modern fringe-pattern-analyzing interferometer with a resolution of 1 x 1 0(-9) and without exclusion of systematic uncertainties owing to optic effe cts of less than 1 nm was used to test a new method of interferometric leng th measurement based on a combination of the reproducible wringing and slav e-block techniques. Measurements without excessive wringing film error are demonstrated for blocks with nominal lengths of 2-6 mm and with high surfac e flatness. The uncertainty achieved for these blocks is less than 1 nm. De formations of steel gauge blocks and reference platens, caused by wringing forces, are investigated, and the necessary conditions for reproducible wri nging are outlined. A subnanometer uncertainty level in phase-change-correc tion measurements has been achieved for gauge blocks as long as 100 mm. Lim itations on the accuracy standard method of interferometric length measurem ents and shortcomings of the present definition of the length of the materi al artifact are emphasized. (C) 2000 Optical Society of America.