The National Bureau of Standards (NBS) was formed by Congress 100 years ago. The early Bureau was a small organization, founded at the beginning of the age of electricity to promote industrial productivity, commerce, technological progress, and the quality of life. It provided a basis for standardizing the measurements and products that are so important to a nation's infrastructure. The original staff numbered 12. There were 15 offices and laboratories. Five areas of optics have been important elements of the Bureau's research for almost it's entire history: atomic and molecular spectroscopy; radiometry; colorimetry; optical properties of materials; and, for the last 40 years, laser science and applications. Research and measurement services have supported national programs ranging from the manufacture of high quality optical glass during two World Wars to the calibration of spectrometers on the Hubble Space Telescope. Pioneers in optical science and metrology at NBS/NIST include many well known scientists, ranging from William Coblentz, who established the field of optical radiometry during his 40 year career from 1905-1945, to William Phillips, who received the Nobel Prize in Physics in 1997 for his research on the laser cooling and trapping of atoms.
Measurement of light is an old subject, though the past 100 years have seen significant advances. 100 years ago, photometry - the art and science of measuring light as it is perceived by people - had the greater technological importance. Even today SI (the metric system) retains a base unit for photometry, the candela. However, early work at NBS included pivotal projects in the field of radiometry - the measurement of the physical characteristics of light. These included the validation of Planck's newly-minted theory of blackbody radiation, determining the radiation constants with good accuracy, and the definitive analysis of the spectral responsivity of human vision, so as to relate photometry to radiometry. This latter work has only increased in importance over the past 75 years as the definition of the candela has changed and improved. Today, NIST makes radiometric, and hence photometric measurements, with unprecedented precision. Cryogenic radiometers based on the principle of electrical substitution measure optical flux with uncertainties of 0.02%. Additional facilities enable measurement of spectral responsivity, spectral radiance, and spectral irradiance. Novel detectors, such as light-traps, allow the best accuracy to be transferred from the primary standards to routinely-used instruments and to calibration customers. Filtered detectors are used to realize photometric scales, radiation temperature scales, and other specialized measurements. Indeed, the story of the metrology of light is the story of continuous improvement, both driven by and enabled by advances in technology. We touch upon some of these as a prelude to the other talks in this Conference.
The National Institute of Standards and Technology (NIST) provides measurement technology, standards, and traceability for much of the optoelectronics industry. This paper covers its support for two major industry segments, the laser industry and the optical communication industry.
Most would assume that the characterization of electronic display quality would be a straightforward process offering few complications. However, what the eye sees can be very difficult to capture accurately and quickly in a meaningful way. With the advent of many new display technologies, there is a need to a level playing field so that different technologies can be compared on an equivalent basis. Orchestrating display metrology to accomplish this is wrought with several difficulties that will be reviewed especially in the areas of stray light management/measurement and meaningful reflection characterization.
New scientific insight and technological developments of the past few years have stimulated renewed enthusiasm for the development of optical frequency standards. Long-standing problems have now been eliminated, and it appears that frequency standards using stable lasers and optical transitions may someday replace modern atomic clocks that are based on microwave transitions.
Experiments in Bose-Einstein condensation provide an unusually direct view of the working quantum wave mechanics. We make use of two internal states of Rb-87 to engineer desired wavefunction patterns, and with the use of simple optical imaging, we characterize the results of these efforts.
The technology to rapidly manipulate and screen individual molecules lies at the frontier of measurement science, with impacts in bio- and nano-technology. Fundamental biological and chemical processes can now be probed with unprecedented detail, one molecule at a time. These single molecule probes are most often fluorescent dye molecules embedded in a material or attached to a target molecule, such as a protein or nucleic acid, whose behavior us under study. The fluorescence from a single dye molecule can be detected, its spectrum and lifetime measured and its absorption or emission dipole calculated. From this information, the rotational and translational dynamics of the fluorophore can be calculated, as can details of its photophysics. To the extent that these properties reflect the properties of the target molecule, we can use these fluorescent tags to probe the dynamics and structure of the target. In this work we discuss the dependence of the physical and photophysical dynamics of fluorescent molecules on their local environment, and we use confocal microscopy to study single molecules in thin films, on surfaces, and in various liquid and gaseous environments.
The basic goal of the Advanced Optics Metrology program in NIST's Manufacturing Engineering Laboratory is to help industry ensure that their measurement results of optical figure and wavefront are traceable. This paper underscores the importance of traceability and reviews the facilities and projects dedicated to achieving that objective.
NIST has a long-standing program for the calibration of extreme ultraviolet optical components. Early activities, which began with the advent of the Synchrotron Ultraviolet Radiation Facility (SURF) almost 40 years ago, centered on the development and characterization of detectors for extreme ultraviolet (EUV) radiation. About a decade ago the program was expanded to include reflectometry of normal- incidence EUV multilayer optics. Both calibrated detectors and EUV optics are used by researchers in private industry, academia, and government, in such diverse fields as EUV lithography, astronomy, and plasma physics. Since the inception of SURF, nearly 800 transfer standard photodiodes have been issued to customers, and over 500 measurements of other EUV optical components have been made. NIST researchers, in collaboration with U.S. companies, have developed new, high-quality radiometric detectors for use throughout the EUV spectral range. We will discuss the history of NIST's involvement in EUV metrology and offer examples of our recent work.
We provide an historical overview of NIST research and development in radiometry for space-based remote sensing. The applications in this field can be generally divided into two areas: environmental and defense. In the environmental remote sensing area, NIST has had programs with agencies such as the National Aeronautical and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) to verify and improve traceability of the radiometric calibration of sensors that fly on board Earth-observing satellites. These produce data used in climate models and weather prediction. Over the years, the scope of activities has expanded from existing routine calibration services for artifacts such as lamps, diffusers, and filters, to development and off-site deployment of portable radiometers for radiance- and irradiance-scale intercomparisons. In the defense remote sensing area, NIST has had programs with agencies such as the Department of Defense (DOD) for support of calibration of small, low-level infrared sources in a low infrared background. These are used by the aerospace industry to simulate ballistic missiles in a cold space background. Activities have evolved from calibration of point-source cryogenic blackbodies at NIST to measurement of irradiance in off-site calibration chambers by a portable vacuum/cryogenic radiometer. Both areas of application required measurements on the cutting edge of what was technically feasible, thus compelling NIST to develop a state-of-the-art radiometric measurement infrastructure to meet the needs. This infrastructure has led to improved dissemination of the NIST spectroradiometric quantities.
The program in atomic spectroscopy at NISt continues to provide accurate reference data on spectral lines and energy levels for a wide variety of important applications. With spectrometers that can record spectra from the extreme ultraviolet (1 nm) to the infrared (18 000 nm), we can measure spectra over a large spectral range. Most of these spectrometers are the most powerful of their type in the world. We recently used out 10.7-m normal-incidence vacuum spectrography to make precision measurements of the wavelengths of lasing lines in a commercial molecular fluorine laser at 157 nm. These results establish standard values to be applied in the design of optics for microlithography at this wavelength. Our high resolution Fourier transform spectrometer is being used to measure wavelengths and transition probabilities for rare-earth atoms and ions th at are used as additives in the production of high intensity discharge lamps. The data allow lamp designers to model the processes occurring in the discharge. Our 10.7-m grazing incidence spectrograph is being used to obtain data for diagnostics of magnetic fusion research plasmas as well as for astronomical applications such as the Chandra X-ray Observatory. Precision laser spectroscopy on neutral Li is being carried out to test the validity of quantum electrodymanics (QED) calculations. Finally, we are continuing to carry out critical complications of wavelengths, energy levels, and transition probabilities and to improve our Atomic Spectra Database on the World Wide Web. These data activities support many applications throughout industry and the scientific community.
This is the first of two papers which describe some of the advances over the last 20 years that have been made in primary scales and supporting techniques which have led to an order of magnitude improvement in the uncertainty of optical radiation measurement scales disseminated to industry and academia. In this paper we concentrate on cryogenic radiometry, laser radiometry and filter radiometry, the latter being the interface between the largely monochromatic primary realizations and the more useable polychromatic scales. The paper reviews some of the history of the underpinning current methodologies and some directions for the future, concentrating on those in which NPL has made a significant contribution.
This is the second part of two papers which discusses some of the applications of the techniques and standards described in part 1. In particular, the realization of spectral irradiance and radiance scales and the radiometric measurement of thermodynamic temperature. The paper also briefly describes some new ways of improving the dissemination of some of these scales both in terms of accuracy and user convenience. It also discusses some specific needs of application areas such as Earth observation and difficulties associated with terminology such as traceability which will need to be addressed in the future to ensure progress at the NMIs is fully exploited in industry. In addition to the more standard radiometric application areas, a brief overview of the demands of new application areas such as appearance are also introduced.
The Space Dynamics Laboratory at Utah State University designed and constructed two identical cryogenic mid- infrared radiometers that will be used as NIST-traceable radiometric calibration transfer standards. The radiometer design is similar to the NIST BXR radiometer and thus may be calibrated at NIST using the same sources and procedures used with the BXR. Important features of these radiometers include a single element, chopped indium antimonide detector cooled by a Stirling-cycle cryocooler, two 8-position filter wheels populated with spectral and neutral density filters, and an indium antimonide focal plane array (FPA) that can be temporarily positioned at the field stop for alignment and diagnostics. This paper presents the design and results of the as-built optical and thermal performance of these radiometers. It also presents the testing set up and calibration philosophy and approach.