To enable our highest accuracy calibrations and NIST advanced research efforts, we maintain and develop methods to provide traceability to the meter via laser frequency/wavelength. The most significant source of uncertainty in most very high accuracy length measurements is the value of the index of refraction of air. The development of accurate refractometers will increase the accuracy of nearly all laser-based length measurements and is crucial to meet increasing demands from industry for high accuracy traceability. Our efforts also enabling new high-accuracy optical wavelength-based methods to realize pressure and temperature.
Laser interferometry, which measures distances in terms of light wavelength, provides the backbone of top-level length metrology in industry and science. This project develops techniques to facilitate the tie between interferometer-based length measurements and the SI definition of length (in terms of the second). Integral to providing this link are:
This project has made important steps toward reaching that goal. Excellent results have been achieved for dry gases (absolute refractometry to ±2 parts in 1010), and current efforts focus on overcoming problems associated with air humidity.
Wavelength metrology
Refractometry
Material measures and reference artifacts
Much of the refractometry work is available for licensing. Patent from 2019 available: Deformometer for Determining Deformation of an Optical Cavity Optic
Requests for specialty measurements of thermal expansion or dimensional stability could be accommodated via cooperative research and development agreement. See mechanisms at the technology partnership office.