NIST standards play major role in laser technology

Sept. 1, 1999
Ask the average American to describe the importance of the Washington, DC, area, and that person probably would cite the federal government and not laser technology.

Ask the average American to describe the importance of the Washington, DC, area, and that person probably would cite the federal government and not laser technology. But the low-profile National Institute of Standards and Technology (NIST), which has one of its two principal facilities just north of the nation's capital in Gaithersburg, MD, is playing an important role in providing technological bedrock for the US laser industry.

NIST's major contribution is in what many would consider a mundane task: developing technology, standards, and procedures for making highly precise measurements of phenomena such as heat and light. Those measurements lay the groundwork for devices, materials, and products from the laser industry and other industries, as well.

NIST, which is part of the US Department of Commerce, employs about 3300 scientists, engineers, and other staff at facilities in Gaithersburg and Boulder, CO. Although its mission includes other projectssuch as overseeing the Advanced Technology Program, under which the federal government helps underwrite the development of commercially important technologiesmuch of the agency's effort is focused on its laboratories in Gaithersburg and Boulder.

For example, the High Accuracy Cryogenic Radiometer (HACR) at the NIST Gaithersburg headquarters is the nation's standard for measurements of optical power. "This is the instrument that acts as the primary standard in relating optical watts to watts in other areas of science," says Jonathan Hardis, a physicist in the division.

Loosely speaking, the HACR essentially consists of a can with a black interior. A laser beam enters through a hole and is absorbed by the black interior surface, heating the can. Separately, researchers also can heat it with an electrical heater, which can be carefully measured. By electrically heating the can at the same level as heat produced by a given laser beam, the NIST researchers determine the equivalent, in electrical watts, of the laser.

Another key instrument is a 2.5-m integrating sphere, a device used to precisely measure the flux of lamps. Ordinarily, to determine the flux produced by a lamp, researchers must measure it at 3000 to 5000 points around the lamp, says physicist Yoshi Ohno. But the sphere, painted white inside, is 98% reflective. The whiteness is so uniform and the reflectiveness so nearly perfect that a visitor standing inside has difficulty perceiving the curve of the sphere around him. Such a perfect surface allows the re searchers to use flux measurements from only one detector, rather than thousands, to extrapolate the lamp's flux in all directions.

Ohno also recently helped develop a method to standardize measurement of the flashing anticollision lights found on aircraft. Without a standard, it was impossible to be sure that the lights were operating correctly, leaving the possibility of aircraft accidents that could have been avoided, said Ohno.

Under a contract from the Federal Aviation Administration (FAA), Ohno developed photometers that can precisely measure the output of a flashing anticollision light. The FAA has approved use of the technique, and NIST has begun offering to calibrate photometers for aircraft manufacturers and airlines.

Optical Technology Division

The HACR and Ohno both are part of the NIST Optical Technology Division, which includes 44 people across five groups dealing with optical temperature and source, optical properties and infrared technology, optical sensors, laser applications, and spectroscopic applications.

One recent area of work is measuring the index of refraction of material for use in optics in the lithography industry. "We're about the only place that's doing that," says Keith Lykke, head of the Optical Sensor Group.

This division also plays an important role in Mission to Planet Earth, a NASA project to extensively monitor Earth from satellites and other platforms. Although the instruments on spacecraft can make phenomenal measurements of the Earth below, one problem has always been in calibrating the instruments so that scientists could have confidence in their measurements. Although the issues being studied by Mission to Planet Earthsuch as the possibility of global warmingare controversial, Albert Parr, chief of the Optical Technology Division, predicts that NIST's involvement in calibrating the measurements will eliminate arguments over the accuracy of the measurements themselves.

Similarly, NIST physicist B. Carol Johnson is working to calibrate NASA's Sea-Viewing, Wide-Field-of-View Sensor (SeaWiFS), which will measure light reflected from the ocean and thereby provide information on the concentrations of phytoplankton in the ocean. Johnson and others in the Optical Technology Division developed the SeaWiFS Quality Monitor, a device containing photodiodes that researchers could take with them on research cruises at sea. The researchers could use the device to check the operation of radiometers used during the cruise that in turn would be used to calibrate satellite observations of larger regions of the ocean.

Other NIST laser support

But NIST's work in technologies of interest to the laser industry is not limited to its Optical Technology Division. Another part of NIST that also is important for the laser industry is the Optoelectronics Division, located in Boulder.

And at the Gaithersburg headquarters, NIST's Electricity Division is enmeshed in developing standards for testing the performance of flat-panel displays (FPDs). That division's work is reflected in Flat Panel Display Measurement Standards set forth by the Video Electronics Standards Association in May 1998. That first edition of the standards provides detailed instructions on how to measure the characteristics of a FPD and discusses the major sources of error to avoid, based on tests performed at the Flat-Panel-Display Laboratory in Gaithersburg. A second version, now in preparation, will include additional types of FPDs such as reflective displays and projective displays. Future work will include even more advanced systems such as head-mounted displays.

The goal, says physicist Ed Kelley, is to give both computer manufacturers and users a common set of standards by which to assess the performance of the flat-panel devices. Says Hardis, "Where NIST has its most value is between buyers and sellers." Or as Kelley, who runs the flat-panel laboratory, puts it, "If you make a bad measurement on a lousy display, you can advertise it as good," in the absence of NIST's standards. "What this does is level the playing field."

About the Author

Vincent Kiernan | Washington Editor

Vincent Kiernan was Washington Editor for Laser Focus World.

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