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Metrology for comparison of displacements at the picometer level



Jack A. Stone Jr., Patrick F. Egan, Jay H. Hendricks, Gregory F. Strouse, Douglas A. Olson, Jacob E. Ricker, Gregory E. Scace, Donavon Gerty


An apparatus capable of comparing displacements with picometer accuracy is currently being designed at NIST. In principle, we wish to compare one displacement in vacuum to a second, equal displacement in gas, in order to determine gas refractive index. If the gas is helium, the refractive index is amenable to high-accuracy ab initio calculations relating refractive index to gas density or to the ratio of pressure and temperature (P/T); the measured refractive index can then be used to infer (P/T) with an accuracy goal of about 1x10^-6 (relative standard uncertainty). If either the pressure or temperature is known, the refractive index measurement will allow us to determine the second quantity. Our goal is to achieve an uncertainty limited primarily by the uncertainty of the Boltzmann constant (before redefinition of SI units, which will give the Boltzmann constant a defined value). The technique is an optical analog of dielectric constant gas thermometry and can be used in a similar manner. The dimensional metrology is uniquely challenging, requiring picometer-level uncertainty in the comparison of the displacements.
Proceedings Title
Proceedings of 5th ASPEN 2013
Conference Dates
November 13-15, 2013
Conference Location


dimensional metrology, Fabry-Perot interferometer, refractive index


Stone, J. , Egan, P. , Hendricks, J. , Strouse, G. , Olson, D. , Ricker, J. , Scace, G. and Gerty, D. (2014), Metrology for comparison of displacements at the picometer level, Proceedings of 5th ASPEN 2013, Taipei, -1, [online], (Accessed July 14, 2024)


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Created July 31, 2014, Updated November 10, 2018