1973—NIST scientists Richard Deslattes and Howard Layer were the first to combine the techniques of X-ray and laser-based optical interferometry—studying interference patterns created by electromagnetic waves—to precisely determine the spacing of atoms in a silicon crystal. This measurement was key to obtaining an improved value for the Avogadro constant, a fundamental constant of nature related to the mole, the unit for "amount of substance" (one of the seven basic units of measure), which in turn may one day lead to a new natural standard of mass. Deslattes also used the atom spacing measurement to establish more accurate X-ray and gamma-ray wavelength standards.
1975-1979—Interferometry, or the analysis of interference patterns of two light beams, is widely used in research. The advent of laser heterodyne interferometers—which detect a change in the phase of one beam due to a change in its path with respect to the other beam—revolutionized high-precision length measurement. In the late 1970s NIST was a leader in incorporating these new devices into various instruments for dimensional measurement, including coordinate measuring machines and the NIST linescale interferometer. For more than 30 years, NIST's linescale interferometer has been the most accurate instrument in the world for measuring lengths up to 1 meter.
1977—NIST physicist Jan Hall developed a laser wavemeter, substantially improving techniques for accurately measuring laser wavelength. The advent of dye lasers that could be "tuned" to emit light at many different single wavelengths would have a profound impact on optical spectroscopy, the study of interactions between radiation and matter. But tunable laser sources could not be exploited until the laser wavelength was matched accurately to atomic energy levels of interest and stabilized to remove fluctuations.
1977—NIST developed the concept of laser "error mapping" of coordinate measuring machines (CMMs). NIST scientists developed techniques for using laser interferometers to characterize the repeatable rigid-body errors of CMMs, increasing the accuracy of the machines by an order of magnitude. Error mapping was crucial to the commercial success of these machines, which now form the backbone of industrial length metrology.