Charles E. Gibson

Realization of the National Institute of Standards and Technology Detector-Based Spectral Irradiance Scale

A detector-based spectral irradiance scale has been realized at the National Institute of Standards and Technology (NIST). Unlike the previous NIST spectral irradiance scales, the new scale is generated with filter radiometers calibrated for absolute spectral power responsivity traceable to the NIST high-accuracy cryogenic radiometer instead of with the gold freezing-point blackbody. The calibrated filter radiometers are then used to establish the radiance temperature of a high-temperature blackbody (HTBB) operating near 3,000 K The spectral irradiance of the HTBB is then determined with knowledge of the geometric factors and is used to assign the spectral irradiances of a group of 1,000-W free-electron laser lamps. The detector-based spectral irradiance scale results in the reduction of the uncertainties from the previous source-based spectral irradiance scale by at least a factor of 2 in the ultraviolet and visible wavelength regions. The new detector-based spectral irradiance scale also leads to a reduction in the uncertainties in the shortwave infrared wavelength region by at least a factor of 2-10, depending on the wavelength. Following the establishment of the spectral irradiance scale in the early 1960s, the detector-based spectral irradiance scale represents a fundamental change in the way that the NIST spectral irradiance scale is realized.

Thermodynamic-temperature determinations of the Ag and Au freezing temperatures using a detector-based radiation thermometer

The development of a radiation thermometer calibrated for spectral radiance responsivity using cryogenic, electrical-substitution radiometry to determine the thermodynamic temperatures of the Ag- and Au-freezing temperatures is described. The absolute spectral radiance responsivity of the radiation thermometer is measured in the NIST Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) facility with a total uncertainty of 0.15% (k=2) and is traceable to the electrical watt, and thus the thermodynamic temperature of any blackbody can be determined by using Planck radiation law and the measured optical power. The thermodynamic temperatures of the Ag- and Au-freezing temperatures are determined to be 1234.956 K (+/-0.110 K) (k=2) and 1337.344 K(+/-0.129 K) (k=2) differing from the International Temperature Scale of 1990 (ITS-90) assignments by 26 mK and 14 mK, respectively, within the stated uncertainties. The temperatures were systematically corrected for the size- of-source effect, the nonlinearity of the preamplifier and the emissivity of the blackbody. The ultimate goal of these thermodynamic temperature measurements is to disseminate temperature scales with lower uncertainties than those of the ITS-90. These results indicate that direct disseminations of thermodynamic temperature scales are possible.

The realization of the NIST detector-based spectral irradiance scale

The realization of a detector-based spectral irradiance scale at the National Institute of Standards and Technology is described. The new scale is established using filter radiometers calibrated for absolute spectral power responsivity traceable to the NIST High-Accuracy Cryogenic Radiometer unlike the previous NIST spectral irradiance scales based upon the gold freezing-point blackbody. The radiance temperatures of a high-temperature blackbody (HTBB) operating near 3000 K are found using calibrated filter radiometers. The spectral irradiances of a group of 1000 W FEL lamps are assigned using the spectral irradiance of the HTBB determined using the knowledge of the geometric factors and the detector-based radiance temperatures. The detector-based spectral irradiance scale leads to a reduction in the uncertainties from the previous, source-based, spectral irradiance scales by at least a factor of two in the ultraviolet and visible wavelength regions, and also leads to a reduction in the uncertainties in the short-wave infrared wavelength region by at least a factor of two to ten, depending on the wavelength. Following the establishment of the spectral irradiance scale in the early 1960s, the detector-based spectral irradiance scale represents a fundamental change in the way that the NIST spectral irradiance scale is realized, and beginning in the calendar year 2001, all spectral irradiance sources are issued using the detector-based scale.

Spectral Radiance Comparisons of Two Blackbodies with Temperatures Determined Using Absolute Detectors and ITS‐90 Techniques

For calibrations of spectral irradiance standards, a high‐temperature blackbody (HTBB) is used as a source of spectral radiance or irradiance as derived from Planck’s radiance law. The temperature of such a blackbody can be determined using radiance ratios to the gold freezing‐temperature blackbody based on the technique described in the International Temperature Scale of 1990 (ITS‐90), or by using a primary thermometer, which is an absolute detector referenced to a cryogenic radiometer. One of the primary motivations of using the detector‐based method is that the uncertainties in the temperature determination of a HTBB can be lower than those assigned using ITS‐90. Previous comparisons of temperatures measured using the two techniques have been at a few, selected wavelengths due to the limited measurement wavelengths of the comparison pyrometer. In this study, the spectral radiances of a HTBB from 250 nm to 2400 nm are assigned using a spectroradiometer from the known spectral radiances of a variable‐tem...

A CCPR international comparison of spectral radiance measurements in the air-ultraviolet

An international comparison of the spectral radiance scales of the National Physical Laboratory (NPL), the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB) was carried out in 1993 and 1994, under the auspices of the Comite Consultatif de Photometrie et Radiometrie (CCPR) of the Comite International des Poids et Mesures (CIPM). The comparison covered the spectral range 200 nm to 350 nm. The transfer standards were deuterium discharge lamps, with examples of the lamps used at each of the participating laboratories included in the comparison to aid in the identification of systematic errors and to gather information on their relative performance. The scales of the laboratories agreed within the combined uncertainties. However, the combined uncertainties were high (an expanded uncertainty with a coverage factor of k = 2 of up to 8 %), and further work is required to reduce the uncertainties associated with the spectral radiance scales of each laboratory. Little difference was observed in the performance of the three different transfer standard sources used.

Synchrotron radiation-based irradiance calibration from 200 to 400 nm at the Synchrotron Ultraviolet Radiation Facility III

A new facility for measuring irradiance in the UV was commissioned recently at the National Institute of Standards and Technology (NIST). The facility uses the calculable radiation from the Synchrotron Ultraviolet Radiation Facility as the primary standard. To measure the irradiance from a source under test, an integrating sphere spectrometer-detector system measures both the source under test and the synchrotron radiation sequentially, and the irradiance from the source under test can be determined. In particular, we discuss the calibration of deuterium lamps using this facility from 200 to 400 nm. This facility improves the current NIST UV irradiance scale to a relative measurement uncertainty of 1.2% (k=2).

Comparison of the absolute detector-based spectral radiance assignment with the current NIST-assigned spectral radiance of tungsten strip lamps

Using a high-temperature black body (HTBB) and filter radiometers calibrated for absolute spectral power responsivity, the spectral output of the black body, whose radiance temperature was determined using the filter radiometers, was used to assign spectral radiance to tungsten strip lamps with a prism-grating monochromator. The spectral radiance of the HTBB was also determined using signal ratios to a tungsten strip lamp calibrated using a scale derived from the radiometric temperature determination of a gold-freezing-point black body. The radiance temperatures found using the two methods were in agreement to 0.5 K near 2900 K, and from 260 nm to 1050 nm, the spectral radiance of the HTBB did not differ more than 0.5 % in radiance from a single-temperature Plancks law as determined using the tungsten strip lamp.

The Development and Characterization of an Absolute Pyrometer Calibrated for Radiance Responsivity

For temperatures above the freezing temperature of silver, the International Temperature Scale of 1990 (ITS‐90) is defined in terms of spectral radiance ratios to one of the silver, gold or copper freezing‐temperature blackbodies using the Planck radiance law. However, due to the use of spectral radiance ratios, the uncertainties in the realization of thermodynamic temperatures using ITS‐90 increase as the square of the temperature ratios. Such increases in the temperature uncertainties can be reduced by using absolute radiometry with pyrometers traceable to cryogenic radiometers, and the resulting temperature uncertainties can be smaller than those measured using the ratio pyrometry as prescribed in ITS‐90. We describe the development and the characterization of an absolute pyrometer (AP1) constructed at NIST and calibrated for absolute radiance responsivity. The calibrations are performed with the pyrometer as a single unit; thus separate measurements of the lens transmittance and the spectral responsiv...

International comparison of radiation temperature scales among five national metrological laboratories using a transfer radiation thermometer

Round-robin measurements with a transfer standard radiation thermometer were organized by the NRLM in the framework of a three-year joint research agreement with the NIST, the IMGC and the PTB: the NPL also took part in this exercise. The aim of the study was to assess the mutual traceability of the ITS-90 temperature scales established by the different laboratories in the high-temperature range (above 1000 °C). The thermometer was a monochromatic (0,65 µm) silicon-detector thermometer belonging to the NRLM. It was circulated in the period from May to July 1993 and was calibrated by all the participants against their local reference thermometers. The temperature interval from 1000 °C to 2000 °C was covered by all the participants, but some extended the range down to 800 °C or up to 2700 °C. The results indicate that all the calibrations agree to within 0,5 °C at 1000 °C and to within 2 °C at 2000 °C.

Results of a NIST/VNIIOFI comparison of spectral-radiance measurements

A comparison of the spectral-radiance scales of the National Institute of Standards and Technology (NIST) and the All-Russian Research Institute for Optophysical Measurements (VNIIOFI) was carried out in 1989 and 1990. The spectral range of the comparison was between 240 nm and 2400 nm. The transfer standards were argon-filled tungsten ribbon filament lamps. The NIST/VNIIOFI agreement was 0,5 % to 1 % in the 240 nm to 800 nm range, and better than 0,5% between 900 nm and 2400 nm. On average, the spectral radiances measured at the VNIIOFI were slightly higher than the NIST values.