Toward subnanometer uncertainty in interferometric length measurements of short gauge blocks

A primary-level comparator, with a reproducibility of 0.2 nm and intended f or 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 experim ents has been developed to measure systematic error associated with nonidea l interferometer optics and deviations from flatness of an auxiliary plate. For specially selected high-grade 6-mm blocks, reproducible wringing has b een 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 th e length measurements is evaluated to be in the 23-nm range for 6-mm blocks . (C) 1999 Optical Society of America.