1970s

1969-1972—NIST scientists achieved nine world-record measurements of laser frequency within just a few years, eventually leading to the redefinition of the meter based on the speed of light. Of particular note is a 1972 record measurement with a novel laser stabilized to a specific frequency of light that interacts strongly with methane gas, ensuring that any other similar lasers will operate at the same frequency so the experiment can be repeated. This measurement, led by NIST physicists Ken Evenson and Jan Hall, resulted in a 100-fold improvement in the accuracy of the accepted value for the speed of light. This design enabled accurate independent measurements of the light's wavelength as well as independent verification of the speed of light measurements. (An overview of this work and other early NIST research related to time and frequency measurements can be found at http://tf.nist.gov/general/pdf/1485.pdf.)

1972—NIST physicist Cary Gravatt developed a method using scattered light from a continuous-wave laser beam to determine the size of particles suspended in air. The device, able to track particle sizes and gather information about their chemistry and concentrations, enabled real-time monitoring of many different types of aerosols including dust in homes, factories, and coal mines as well as clouds, fuels, paint sprays, and smokestacks. Gravatt developed the monitor as part of the NIST Measures for Air Quality Program, which provided technical support for the U.S. Environmental Protection Agency.

 

 

 

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.

1976-1980s—Bathing a partially-ionized (electrically charged) cloud of atoms with just the right frequency of tunable laser light, an interdisciplinary research team in NIST's laser chemistry program observed an unexpected voltage change across electrodes ionizing the atoms. The novel phenomenon, coined the optogalvanic effect, enabled the development of laser-enhanced ionization, a practical technique that needed no complex optical detectors and could detect tiny amounts of chemical elements in samples prepared as liquid solutions and vaporized into flames. The samples consisted of everything from metal alloys to contaminated water to animal blood. Soon after this discovery, NIST built a world-recognized, state-of-the-art laser-enhanced ionization facility. Laser-enhanced ionization remained the most sensitive atomic-detection technique for several years before new technologies succeeded it.

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.

1978—NIST scientists led by David Wineland achieved the first successful demonstration of laser cooling, concurrently with another research group in Germany, opening a new field of research on ultracold atoms. Laser cooling involves the use of laser beams to push atoms with radiation pressure, thereby slowing and cooling the atoms to near absolute zero, the coldest possible temperature. This first NIST demonstration was performed with ions (electrically charged atoms). The breakthrough led to research by groups around the world on laser cooling and trapping of neutral atoms, laying the groundwork for later Nobel prizes for NIST physicists. This work also led to the development of laser-cooled atomic clocks, the current state of the art in time and frequency standards. In 2007, Wineland was recognized with U.S. National Medal of Science. http://www.nist.gov/public_affairs/releases/wineland082508.cfm