Erratum: Statistical Interpretation of Key Comparison Reference Value and Degrees of Equivalence.

[This corrects the article on p. 439 in vol. 108.].

Statistical Interpretation of Key Comparison Reference Value and Degrees of Equivalence.

Key comparisons carried out by the Consultative Committees (CCs) of the International Committee of Weights and Measures (CIPM) or the Bureau International des Poids et Mesures (BIPM) are referred to as CIPM key comparisons. The outputs of a statistical analysis of the data from a CIPM key comparison are the key comparison reference value, the degrees of equivalence, and their associated uncertainties. The BIPM publications do not discuss statistical interpretation of these outputs. We discuss their interpretation under the following three statistical models: nonexistent laboratory-effects model, random laboratory-effects model, and systematic laboratory-effects model.

The Candela and Photometric and Radiometric Measurements.

The national measurement system for photometric and radiometric quantities is presently based upon techniques that make these quantities traceable to a high-accuracy cryogenic radiometer. The redefinition of the candela in 1979 provided the opportunity for national measurement laboratories to base their photometric measurements on optical detector technology rather than on the emission from high-temperature blackbody optical sources. The ensuing technical developments of the past 20 years, including the significant improvements in cryogenic radiometer performance, have provided the opportunity to place the fundamental maintenance of photometric quantities upon absolute detector based technology as was allowed by the 1979 redefinition. Additionally, the development of improved photodetectors has had a significant impact on the methodology in most of the radiometric measurement areas. This paper will review the status of the NIST implementation of the technical changes mandated by the 1979 redefinition of the candela and its effect upon the maintenance and dissemination of optical radiation measurements.

Vibrational Branching Ratios and Asymmetry Parameters in the Photoionization of CO2 in the Region Between 650 Å and 840 Å.

The vibrational branching ratios and asymmetry parameters for CO2 have been determined in the wavelength region of 650 Å to near the ionization onset at about 840 Å. The study was performed using synchrotron radiation from the Daresbury storage ring that was dispersed with a 5 m grating monochomator that afforded resolution of 0.1 Å to 0.2 Å. This resolution allowed the study of the branching ratios and asymmetry parameters with enough detail to see the changes in the parameters within the pronounced autoionization structure in CO2 in this wavelength region. While the electron spectrometer resolution was not sufficient to resolve the spin orbit and Renner-Teller splitting in the photoelectron spectra, we are able to fit the data with a model that identifies the major structure in terms of the symmetric stretch and elements of the asymmetric stretch and bending modes. A calculation of the expected relative vibrational excitations based upon the Franck-Condon principle clearly showed non-Franck-Condon behavior in some of the vibrational-electronic transitions.

An alternative approach to antifouling based on analogues of natural processes.

A number of marine organisms are able to resist fouling pressure and remain essentially free of fouling. Some organisms are totally devoid of even the first stages of biofilm formation involving bacteria and microalgae. A key feature in recent research has been the realisation that previous low adherence technology is an insufficient technical solution and that natural models, based on marine and other organisms, incorporate other passive techniques for fouling resistance. These characteristics may be incorporated into physical analogues of the natural processes. This paper describes ways of producing physical analogues of some such characteristics, the application of such techniques to surfaces in the marine environment and the environmental impact. The paper includes some results of recent trials and a cost comparison.

Ultraviolet radiometry with synchrotron radiation and cryogenic radiometry.

The combination of a cryogenic radiometer and synchrotron radiation enables detector scale realization in spectral regions that are otherwise difficult to access. Cryogenic radiometry is the most accurate primary detector-based standard available to date, and synchrotron radiation gives a unique broadband and continuous spectrum that extends from x ray to far IR. We describe a new cryogenic radiometer-based UV radiometry facility at the Synchrotron Ultraviolet Radiation Facility II at the National Institute of Standards and Technology. The facility is designed to perform a variety of detector and optical materials characterizations. The facility combines a high-throughput, normal incidence monochromator with an absolute cryogenic radiometer optimized for UV measurements to provide absolute radiometric measurements in the spectral range from 125 nm to approximately 320 nm. We discuss results on photodetector characterizations, including absolute spectroradiometric calibration, spatial responsivity mapping, spectroreflectance, and internal quantum efficiency. In addition, such characterizations are used to study UV radiation damage in photodetectors that can shed light on the mechanism of the damage process. Examples are also given for UV optical materials characterization.

The NIST Detector-Based Luminous Intensity Scale.

The Système International des Unités (SI) base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps to be carried out with a relative expanded uncertainty (coverage factor k = 2, and thus a 2 standard deviation estimate) of 0.46 %, almost a factor-of-two improvement. A group of eight reference photometers has been constructed with silicon photodiodes, matched with filters to mimic the spectral luminous efficiency function for photopic vision. The wide dynamic range of the photometers aid in their calibration. The components of the photometers were carefully measured and selected to reduce the sources of error and to provide baseline data for aging studies. Periodic remeasurement of the photometers indicate that a yearly recalibration is required. The design, characterization, calibration, evaluation, and application of the photometers are discussed.

National Institute of Standards and Technology high-accuracy cryogenic radiometer.

A high-accuracy cryogenic radiometer has been developed at the National Institute of Standards and Technology to serve as a primary standard for optical power measurements. This instrument is an electrical-substitution radiometer that can be operated at cryogenic temperatures to achieve a relative standard uncertainty of 0.021% at an optical power level of 0.8 mW. The construction and operation of the high-accuracy cryogenic radiometer and the uncertainties in optical power measurements are detailed.

Cryogenic Blackbody Calibrations at the National Institute of Standards and Technology Low Background Infrared Calibration Facility.

The Low Background Infrared Calibration Facility (LBIR) at the National Institute of Standards and Technology has been in operation for calibration measurements of the radiant power emitted from infrared radiation (IR) sources, such as cryogenic blackbodies, for more than 2 years. The IR sources are sent to NIST by customers from industry, government, and university laboratories. An absolute cryogenic radiometer is used as the standard detector to measure the total radiant power at its aperture. The low background is provided by a closed cycle helium refrigeration system that maintains the inner parts of the calibration chamber at 20 K. The radiance temperature of the blackbody is deduced from the measured power and compared with the blackbody temperature sensor data. The calibration procedures and data analysis are illustrated using the measurements of a typical blackbody.

National Institute of Standards and Technology detector-based photometric scale.

The Système International base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps with an expanded uncertainty of 0.46%, almost a factor-of-2 improvement. A group of eight reference photometers has been constructed with silicon photodiodes, matched with filters to mimic the Commission Internationale de l'Eclairage spectral luminous efficiency function for photopic vision.The design, characterization, calibration, evaluation, and further application of the photometers are discussed.

Characterization of an absolute cryogenic radiometer as a standard detector for radiant-power measurements.

An active cavity radiometer of the electrical substitution type with a cone receiver that operates at 2-4 K has been developed for measuring radiant fluxes in the dynamic range of 20 nW to 100 microW within an uncertainty of +/-1% (2sigmalevel). It is a broadband absolute detector with a flat overall absorption efficiency that is >99% for radiation from the visible to long-wavelength IR. The system is designed based on thermal modeling and experimental measurements of concepts. It has been installed in the cryogenic chamber for low-background infrared radiation calibrations at the National Institute of Standards and Technology (NIST) for testing cryogenic blackbody sources, detectors, and optical components. Its time constant, responsivity, and nonequivalence error have been measured. They are in agreement with design predictions. Radiant power measurements of an amplitude-stabilized He-Ne laser beam with the radiometer and an industry standard photodiode detector, QED-200, have been intercompared and found to be in agreement. The intercomparison ratio of the measurements with the absolute cryogenic radiometer and QED-200 was 1.004 in the 75-100-microW range with an uncertainty of 0.5% (the 3sigma level).