High-temperature Blackbody Research Articles

Developments for a New Spectral Irradiance Scale at the National Institute of Standards and Technology.

Recent developments for a new spectral irradiance scale realization at the National Institute of Standards and Technology have been targeted to reduce the present relative expanded uncertainties of 0.67 % to 4.34 % (coverage factor of k = 2 and thus a 2 standard deviation estimate) in the spectral irradiance scale to 0.17 % for the range from 350 nm to 1100 nm. To accomplish this goal, a suite of filter radiometers calibrated using NIST’s high accuracy cryogenic radiometer have been used to measure the temperature of a high-temperature black-body. A comparison of the filter radiometer calibrations with the spectral irradiance scale along with an evaluation of the black-body calibration technique have been performed. With the aid of a monochromator, the calibrated filter radiometers will then be utilized to calibrate primary and secondary spectral irradiance standard lamps at NIST.

Precision blackbody sources for radiometric standards

The precision blackbody sources developed at the All-Russian Institute for Optical and Physical Measurements (Moscow, Russia) and their characteristics are analyzed. The precision high-temperature graphite blackbody BB22p, large-area high-temperature pyrolytic graphite blackbody BB3200pg, middle-temperature graphite blackbody BB2000, low-temperature blackbody BB300, and gallium fixed-point blackbody BB29gl and their characteristics are described.

High-temperature miniature blackbody radiation sources

Various high-temperature blackbody sources for quantitative energy measurements in the IR spectral region are developed. Techniques that ensure a stable operation of the sources at high temperatures are described. The developed blackbody models with maximum temperatures of 2000, 2500, and 3000 K can also operate at other temperatures. Graphite is used as a material for radiators. These blackbodies can be used successfully in radiometric measurements in UV and visible spectral ranges. Blackbodies as high-brightness sources may find wide application in solving the problems of multipass spectroscopy. The blackbody sources developed as rocket engineering has progressed have remained outside the knowledge of foreign scientists.

A method of realizing spectral-radiance and irradiance scales based on comparison of synchrotron and high-temperature black-body radiation

Improvements in synchrotron radiation and high-temperature black-body sources will provide a method of realizing scales of spectral radiance and irradiance with uncertainties comparable with those provided by absolute cryogenic radiometers. This paper discusses planned improvements in the synchrotron radiation facility at the National Institute of Standards and Technology (NIST), and how these improvements can be exploited to accurately measure the temperature of a high-temperature black body developed at the All-Russian Research Institute for Optophysical Measurements (VNIIOFI), thus allowing substantial improvement in radiometric scales.

Comparison of filter radiometer spectral responsivity with the NIST spectral-irradiance and illuminance scales

Narrowband filter radiometers are being used in the development of a new method of irradiance scale realization at the National Institute of Standards and Technology (NIST). To improve the accuracy of the current spectral-irradiance scale, we propose to eliminate several steps from the calibration process and to use the filter radiometers and a high-temperature black body in realizing the scale. Ultimately, the filter radiometers will be calibrated against a trap detector measured at the NIST High Accuracy Cryogenic Radiometer, which maintains an expanded uncertainty at 633 nm of 0,0266% for a coverage factor of k = 2. In this work, the filter and detector were calibrated as a unit using the NIST Detector Comparator Facility, and the aperture areas were measured by flux comparison with a uniform source. Six filter radiometers covering the spectral range 350 nm to 1100 nm were used to measure a known irradiance source; the measurements agreed with predictions to within 1%. Comparisons were also conducted with three NIST standard photometers, and similar agreement was observed. Since the irradiance source and the photometers were calibrated using independent methods, our results not only verify the calibration of the filter radiometers but also imply that the NIST scales of spectral irradiance and illuminance are consistent. Future plans include characterization of a high-temperature black body and the calibration of quartz-halogen irradiance lamps using this black-body source.

The characterization of a high-temperature black body as the basis for the NPL spectral-irradiance scale

The paper describes the stabilization and radiometric characterization of a Russian-made high-temperature black body. The black body is actively controlled at around 2500 K, emitting radiation which is stable in radiance to ±0,01% at 800 nm, over several hours. Techniques are described which show how the radiance of the black body can be maintained at a constant level from day to day. The techniques used to determine the absolute spectral radiance of the black body using a laser-characterized monochromator are also described.

Realization of the lumen on the basis of a large-aperture high-temperature black body

A method of realizing the lumen on the basis of recent developments in the field of black-body design is proposed as an alternative to the traditional goniophotometric technique. It is shown that a precision, large-area, high-temperature black body (HTBB) operating at temperatures up to 3200 K could be used for the direct realization of the lumen.

Black-body radiometry

Radiometry based on black bodies remains one of the fundamental fields of radiometry. Black bodies are widely used as standard sources in radiometry of noncoherent optical radiation from the ultraviolet to the far-infrared spectral regions. Outstanding progress in radiometry has been made in the last decade due to development of high-precision cryogenic radiometers, which have made it possible to decrease the measurement uncertainty to 0,01%. New technology and optical physics call for significant improvement in the accuracy of black-body-based radiometry and the practical realization of spectral radiance and irradiance scales having an accuracy of 0,1%. However, the accuracy of black-body-based radiometry is now limited by the accuracy of thermodynamic temperature measurements of a radiating cavity. For example, the uncertainty of spectral radiance and spectral irradiance scales is from 0,5% to 1% in the UV due to uncertainties in pyrometric measurements. The required uncertainty of modern black-body-based radiometry is about 0,1%. This can be achieved by using the latest advances in the field of high-precision radiometric instrumentation, such as absolute radiometers, large-area high-temperature black bodies and synchrotrons.

Reproducibility of the lumen based on a wide-aperture high-temperature black body

Together with traditional methods for establishing the standard unit of luminous flux, the lumen, the possibility is examined for the production of a standard based on recent development at VNIIOFI (All-Union Scientific Institute for the Study of Optical Physics and Engineering) in the area of high-temperature black body construction.

Computer Simulation of Photophoretic Force on Rapidly Vaporizing Heterogeneous Droplet

The theoretical/computational study is focused on the photophoretic (radiometric) effect caused by nonuniform absorption of anisotropic, high-temperature thermal radiation within a layered droplet. Transient values of the photophoretic force acting on the shrinking droplet are estimated by numerical integration of the momentum flux carried by vapor molecules interacting with the droplet's surface of nonuniform temperature. The corresponding stress tensor of the surrounding nonequilibrium gas is calculated by application of the results of the kinetic theory of evaporation of small droplet suspended in its own vapor. The radiant heat dissipation within the microheterogeneous, layered droplet is simulated by an application of the Monte Carlo method. Specific computations are performed for small droplets of ultrafine coal-water slurry (CWS) suspended in superheated steam and irradiated from one side to a high-temperature blackbody radiation. The conditions are simulating the situation of primary atomized CWS ...

National Primary Radiometric Standards of the USSR

A versatile combined primary standard of the USSR has been established at VNIIOFI for the realization of radiometric units. The standard is based on two black bodies, operable at temperatures from 400 to 3000 K, and an absolute radiometer. Units of both spectral and broadband quantities are reproduced within the 0,2 μm to 25 μm range. A black-body radiator made of niobium carbide and graphite is used over the temperature range of 1500-3000 K, while that for the lower temperatures from 400 to 1200 K is a heat-pipe with a sodium heat-transfer medium. In order to determine the thermodynamic temperature T of the high-temperature black body, relative values of radiant flux Pe (Ti) and spectral radiance Leλ (λi, Ti) at several temperatures Ti are found. The method allows realization of radiometric and photometric quantities irrespective of the International Practical Temperature Scale (IPTS-68). The absolute radiometer used is of a special design and has a control system capable of maintaining the conical receiving cavity at constant temperature throughout the measurement process. The absolute radiometer is intended to realize radiometric units as well as to measure the spectral sensitivity of radiation receivers.

Light absorption in laser-heated cavities

The absorption of laser light in 0.25–1 mm diameter gold cavities, irradiated for the purpose of generating high-temperature blackbody radiation with intense laser radiation of either λ=0.44 μm or λ=1.3 μm wavelength, was investigated. For λ=0.44 μm radiation the absorption exceeded 0.9 for all conditions, but dropped to only 0.3 for the smallest cavities irradiated at λ=1.3 μm. Entrance hole and cavity filling with plasma seems important for the understanding of the observations.

Intercomparison between two independent primary radiometric standards in the visible and near infrared: a cryogenic radiometer and the electron storage ring BESSY

An intercomparison has been performed in the visible and near infrared between two radiometric standards: the electron storage ring BESSY and a cryogenic absolute radiometer. The spectral irradiance of the continuum source BESSY can currently be predicted with a relative systematic uncertainty of 3 × 10−3, whereas the radiant power of monochromatic laser radiation can be measured by the cryogenic radiometer with a relative systematic uncertainty of 10−4. In this intercomparison the responsivity S of a specially designed transfer radiometer was measured using synchrotron radiation (SSR) and the cryogenic radiometer (SRAD). The mean of the ratios SRAD/SSR for different measurement conditions was 1.0013 with a standard error of the mean of 0.0006 for a wavelength of 676 nm and 0.9990 with a standard error of 0.0007 for a wavelength of 799 nm. The systematic uncertainty of the ratio is 3.8 × 10−3 caused by the uncertainty of SRAD of 1.5 × 10−3 and by the uncertainty of SSR of 3.5 × 10−3. Both radiometric standards agree well within the combined systematic uncertainties of the two methods. The result confirms the 3 × 10−3 uncertainty of BESSY. This source standard has therefore a smaller uncertainty than present source standards based on high temperature blackbody radiators. The work also demonstrates how detector- and source-based radiometric standards can be intercompared or transferred between laboratories with a relative uncertainty of <3 × 10−3.

Reproducing the units of radiation strength and energy intensity for continuous-wave continuous-spectrum optical radiation in the wavelength range 0.2?10.6 ?m

This paper discusses a state special standard for the units of radiation strength and energy illumination for continuous optical radiation with a continuous spectrum in the wavelength range 0.2-10.6 micrometers. A major unit in the standard is the high-temperature black body. The units reproduced by the standard are defined on the basis of Stefan's law with allowance for the geometrical parameters. The working standard is provided by a suite consisting of a radiator, a comparator, and a recording system. The state special standard for the units of energy intensity and radiation strength consists of the following means of measurement: the emitter, the automatic-control system for the temperature, the temperature-measurement system for the emitter, the comparator, and the recording system and this scheme is illustrated.

High-temperature radiators for standards in energy photometry

This paper describes the development of new radiators as high-temperature black bodies as basic units providing high meteorological characteristics in the state primary standard for the units of EBSD, RSSD, and EISD, as well as in the state special standard for RS and EI, and in the corresponding working standards, all of which cover a wide spectral range. Various technical specifications are listed which should be satisfied by the emitters in the state standards. On the basis of the physical and technological properties, niobium carbide is found to be the most suitable material for making the emitter for the state primary standard. The black bodies in the state standards in each case consist of two coaxial tubes heated by passing a current and electrically connected in series as shown. The basic dimensions of the KUPVM cavity are given. As the state special standard for EI does not require the highest possible temperatures, the material was chosen to provide the maximum effective emissivity and this material was high-modulus carbonized carbon-plastic KUPVM. A feature of the black bodies for the IR range was that the radiating cavity was heated by a thermal tube.

Active cavity radiometric scale, international pyrheliometric scale, and solar constant

The active cavity radiometer type II, a new and accurate standard detector, has been developed for the absolute measurement of optical radiant flux. The active cavity radiometric scale (ACRS), defined by the active cavity radiometer (ACR), and the international pyrheliometric scale (IPS), defined by a U.S. standard angstrom pyrheliometer, have been compared in recent experiments. Simultaneous measurements of solar irradiance demonstrated an average systematic difference between the two scales of 2.2%, the measurements on the ACRS exceeding those on the IPS. An analytical study of the sensitivity of the ACR to sources of experimental error is presented. The uncertainty in the ACRS is found to be less than +--0.5% at the one solar constant level relative to the absolute scale based on fundamental physical principles. In August 1968 two ACR's measured the solar irradiance at an altitude of 25 km in a balloon-flight experiment. The solar-constant value derived from this measurement was Ho ---- 137.0 mw/cm . Scales for the measurement of radiant energy are established with respect to fundamental physical concepts by standard detectors or standard emitters of radiant energy. Establishment of a scale of radiomerry by a standard emitter usually involves the irradiance of a suitable (nonstandard) detector by a high-temperature blackbody source of thermal radiation. If the properties of the source and the charac

International Comparison of Measurements of Irradiance

A description is given of the scale of total irradiance maintained at the National Research Council. This scale, in contrast with other national scales, is derived from a low temperature (50 to 150 °C) blackbody, rather than from a high temperature (> 1000 °C) blackbody or an absolute radiometer. The irradiance from three tungsten-filament lamps has been measured on this scale as part of an international programme to intercompare irradiance scales. The results of several tests for systematic errors in these measurements are discussed.

A High-Temperature Blackbody Radiation Source

Abstract : A high-temperature blackbody radiation source, consisting of an electrically heated graphite tube with a small centrally located hole through one wall, was developed for use as a secondary standard in the calibration of radiometric and spectrometric instruments. The spectral emissivity of this source, at 0.65 microns, was calculated by the DeVos method, for which graphite emissivities and temperature gradients were measured in situ with an optical pyrometer. The values of source emissivity ranged from 0.9981 = 0.0004 at 1000C to 0.9997 = 0.0002 at 2000C.

An Evaluation of an High Temperature Blackbody As a Working Standard of Spectral Radiance

For those interested in measuring the spectral radiance of high-intensity arcs, especially in the ultraviolet region, the 3000 degrees C blackbody has several advantages over the conventional tungsten ribbon filament standard of spectral radiance. At a wavelength of 250 nm, it is between two and three orders of magnitude more intense and could have 30% to 40% less uncertainty in its spectral radiance. Moreover, by using the blackbody, measurements could be extended to wavelengths shorter than 250 nm. On the other hand, the intensity advantage of the blackbody can be nearly eliminated by operating and calibrating a tungsten standard-type lamp well over its rated current. Tests have shown that the stability of these lamps operated at 45 A and 50 A is suitable for calibration purposes.

Spectral Characteristics of Exploding Wires for Optical Maser Excitation

As pulsed light sources, exploding wires can be used to provide intense narrow spectral lines as well as the characteristic continuum of very high temperature blackbodies. The surface brightness depends on the wire material and conditions under which the wire is exploded. Optimum conditions for 100–500-μsec long light pulses from wires exploded in air have been found for tungsten, tantalum, and molybdenum wires 0.005 to 0.010 in. in diameter for energy inputs of 3000 J or more. Wires exploded in small diameter vacuum tubes (1–20 μ of Hg) radiate as blackbodies, but narrow line spectra are produced in enclosures of larger dimensions. In the visible and ultraviolet regions of the spectrum the spectral radiance of air-exploded wires is one to three orders of magnitude greater than that of conventional flash lamps. Vacuum-exploded wires have spectral radiance another factor of eight greater. Excitation of various optical masers with exploding wires is discussed.