A non-contacting length comparator utilizing two specially designed photo-electric micro-scopes has been constructed. Performance tests of this comparator, using lapped and polished steel surfaces demonstrate a resolution of -1 nanometer, a precision of--10 nanometers, and a linear range in excess of 50 micrometers.
A. W. Hartman,
F. W. Rosberry,
J. Arol Simpson,
"A Non-Contacting Length Comparator with 10 Nanometer Precision," Optical Engineering 12(3), 120395 (1 June 1973). https://doi.org/10.1117/12.7971639