Spectral Emissivity Measurements Research Articles

The First Nitride Laser Diode on Silicon Carbide

AbstractThis paper reports the events at NCSU leading up to and including those of June 5, 1997 which produced the first demonstration of a nitride laser diode on silicon carbide – and the very first nitride laser demonstration outside of Japan. All of the laser diode samples tested at NCSU were designed, grown, and fabricated into cleaved cavity test structures at Cree Research. Laser testing at NCSU consisted of spectral emission versus current measurements, light output power versus current (L-I) measurement, and light output polarization measurements versus current. The first successful laser on silicon carbide emitted at 402.6 nm. Subsequently, lasers displaying outputs ranging from 402.6 to 430.2 have been successfully tested at NCSU.

Modelling the influence of surface emittance and atmospheric transmittance on Martian spectra

Currently developed studies of radiance of the surface and the atmosphere of Mars are presented. In our modelling we have taken into consideration slant path geometry, various states of the atmosphere and the surface of Mars. Preliminary laboratory measurements of spectral emissivity are used in calculations in order to account for real variations as a function of wavelength. The work presented here is directly connected with the measurements to be carried out by the Infrared Planetary Fourier Spectrometer (PFS) during the Martian mission planned to be launched in November 1996. This instrument works in the wavelength range from 1.2 to 45 μm with a resolution of 2 cm −1 and is optimised for atmospheric and surface studies. At present we limit our simulation to the spectral range from 5 to 13 μm, where some of the most relevant surface features are present.

Simultaneous measurements of normal spectral emissivity by spectral radiometry and laser polarimetry at high temperatures in millisecond-resolution pulse-heating experiments: Application to molybdenum and tungsten

Spectral radiometry and laser polarimetry are two independent techniques for the measurement of spectral emissivity of materials. In this paper, a high-speed system is described for the rapid measurement of normal spectral emissivity of a specimen based on the simultaneous utilization of the two techniques. One of the goals of this work to ascertain the accuracy of the laser polarimetry technique in measurement of normal spectral emissivity at high temperatures. To accomplish this goal, the normal spectral emissivities, in the vicinity of 0.633μm, of molybdenum and tungsten were measured by the two techniques over the temperature range 2000 to 2600 K. The results obtained by the two techniques are in agreement within 1%. The total uncertainty (two-standard deviation level) in measurement of emissivity by either spectral radiometry or laser polarimetry technique is estimated to be not more than + 2%.

Spectral emissivities in the visible and infrared of liquid Zr, Ni, and nickel-based binary alloys

This article reports: (i) values of the spectral emissivities at λ=0.633 μm for liquid Zr, Ni, Ni–25% Sn, Ni–32.5% Sn, Ni–40% Nb, and Ni–75% Zr over a wide temperature range including undercooled and superheated conditions, (ii) experimentally determined infrared radiance temperatures (effective center wavelength about 2.0 μm) as functions of true temperature, and (iii) derived values of the spectral emissivity of these liquid materials in the infrared. Based on the thermal arrest, which occurs upon heating the solid at the melting point, we also report melting points for some of the alloys. For zirconium, temperature dependence of emissivity is reported at other wavelengths in the visible. For Ni–75% Zr, the emissivity dependence on wavelength was determined and compared with previously reported results for liquid zirconium and nickel. The spectral emissivity measurements were obtained using pulsed-dye laser ellipsometry on electromagnetically levitated liquid metals and the radiance temperatures of the specimens were recorded using three pyrometers. Two of these pyrometers had an operating wavelength near 650 nm. The third pyrometer had an operating wavelength range of 1–2.5 μm. Most of the materials studied exhibited moderate temperature dependence of the optical properties and emissivities. Only nickel and zirconium could be undercooled significantly in our apparatus. The infrared and 0.633 μm emissivities of the materials were consistent with the behavior of a typical metal showing emissivity variations with wavelength on the order of −0.07 μm−1.

Direct measurement of spectral emissivity of liquid Si in the range of visible light

Normal spectral emissivity of liquid Si was determined by direct measurement of thermal radiations from a surface of the Si melt and a blackbody cavity. The spectral emissivity has little dependence on the wavelength. The emissivity is 0.27 for the wavelength from 500 to 800 nm and is about a half of that of solid silicon at the melting point. Temperature dependence of the emissivity is very small in the temperature range from the melting point to 1550 °C. Free-electron model with a plasma frequency and relaxation time of the order of 1016 Hz gives a good agreement with the experimental result. That indicates the dominant effect of the free electrons on the optical properties of the liquid Si.

95/02140 Measurements of total and spectral emissivities of some ceramic fibre insulation materials

95/02140 Measurements of total and spectral emissivities of some ceramic fibre insulation materials

Novel Experimental Technique for Measuring High-Temperature Spectral Emissivities

A novel experimental technique for the measurement of spectral emissivities in the temperature range 500 to 1000°C of materials that are both poorly thermally conducting and have a high level of transparency is presented. A Fourier transform infrared spectrometer (FT-IR) is used to compare the spectral radiance from a nearly isothermal, but rapidly cooling, sample to that of a reference blackbody. Experimental results obtained from metal metaborate samples and a theoretical analysis of the technique show the effectiveness of this method, particularly for the case of molten samples.

New experimental facility for measurement of total and spectral emissivities of various thermal protection materials and coatings at high temperatures

New experimental facility for measurement of total and spectral emissivities of various thermal protection materials and coatings at high temperatures

Spectral and total emissivity measurements of highly emitting materials

Carbon, carbides, and nitrides are materials having a relatively high emissivity over the entire spectral range. They are important both as a material and as material components of composites for high-temperature applications, e.g.. in space technology (reusable space transport systems) or energy systems (hot gas turbines). The normal total and spectral emissivities of these three materials have been investigated in the temperature range 1000 to 2000 K and at wavelengths between 0.6 and 6.8 μm. The results have been used to interpret emissivity results of fiber-matrix composites. They are also discussed with regard to potential application as reference materials for high-temperature emissivity measurements.

New automated apparatus for the measurement of spectral emissivity of nonconducting materials by high-speed spectrometer

New automated apparatus for the measurement of spectral emissivity of nonconducting materials by high-speed spectrometer

An intercomparison of normal spectral emissivity measurements between NPL (UK) and IMGC (Italy)

An intercomparison of normal spectral emissivity measurements between NPL (UK) and IMGC (Italy)

Surface and bulk absorption characteristics of chemically vapor-deposited zinc selenide in the infrared

<p>Chemically vapor-deposited zinc selenide exhibits outstanding properties in the infrared and has been established as a prime material for transmissive optics applications. Here we present and discuss data relating to the surface and the bulk absorption forward-looking infrared- (FLIR-) grade chemically vapor-deposited ZnSe, at wavelengths (2-20 µm) and temperatures (100-500 K) of current interest.</p><p>This investigation is based on both spectral emittance measurements and infrared transmission spectroscopy performed in the context of a systems development program. Surface effects can be detected at wavelengths of up to 14 µm and usually predominate at wavelengths of less than 8 µm. Fractional surface absorptions are temperature independent from approximately 200 to 400 K and can be fitted to a Fourier series, at wavelengths ranging from 3.5 to 13.5 µm. The bulk absorption coefficient (βv) is strongly dependent on temperature as well as wavelength, but it can be approximated by a bivariate polynomial expressin that yields recommended values. At wavelengths λ ≲ 10 µm, βv decreases with increasing temperature; it is shown that a wavelength-independent Debye-Waller factor provides a correct description of the temperature dependence, thus pointing to infrared-active localized modes. At wavelengths λ ≳ 14 µm, βv increases with temperature and exhibits temperature dependencies (T(1.7), T(2.6)) that reflect three- and four-phonon summation processes. Finally, an analysis of the temperature dependence of βv at 10.6 µm demonstrates that the intrinsic lattice dynamical contribution to bulk absorption at this wavelength should be close to 4 × 10(-4) cm(-1), in accord with the results of earlier laser calorimetry tests performed on exceptionally pure laser-grade chemically vapor-deposited ZnSe.</p>

Rare-earth garnet selective emitter

Thin film (Ho)-yttrium aluminum garnet (YAG) and Er-YAG emitters with a platinum substrate exhibit high spectral emittance in the emission band (ελ≊0.75, 4I15/2–4I13/2, for Er-YAG and ελ≊0.65, 5I7–5I8 for Ho-YAG) at 1500 K. In addition, low out-of-band spectral emittance, ελ&amp;lt;0.2, suggest these materials would be excellent candidates for high efficiency selective emitters in thermophotovoltaic (TPV) systems operating at moderate temperatures (1200–1500 K). Spectral emittance measurements of the thin films were made (1.2&amp;lt;λ&amp;lt;3.0 μm) and compared to the theoretical emittances calculated using measured values of the spectral extinction coefficient.

Spectral emissivity measurements of land-surface materials and related radiative transfer simulations

Spectral radiance measurements have been made in the laboratory and in the field for deriving spectral emissivities of some land cover samples with a spectroradiometer and an auxiliary radiation source in the wavelength range 2.5–14.5 μm. A easy and quick four-step method (four step to measure the sample and a diffuse reflecting plate surface under sunshine and shadowing conditions, respectively) has been used for simultaneous determination of surface temperature and emissivity. We emphasized in-situ measurements in combination with radiative transfer simulations, and an error analysis for basic assumptions in deriving spectral emissivity of land-surface samples from thermal infrared measurements.

Radiative heat transfer in pulverized-coal-fired boilers—Development of the absorptive/reflective character of initial ash deposits

Emission Fourier transform, infrare (FTIR) spectroscopy data provide in situ, time-resolved, spectralemissivity measurements for ash deposits generated from two U.S. Powder River Basin coals. The first 3h of deposit growth on a tube in cross flow in a pilot-scale furnace detail the development of surface emissivity with time. Measured emissivities vary significantly with wavelength, indicating the influence of the physical properties and chemical composition of the deposit. At long wavelength (>7 μm), emission features exhibit characteristics of silica, sulfates, and silicates. The spectral emissivity measured in this region approaches a steady value due to an increase in deposit thickness and the size of particles in the deposit. In contrast, deposits are not opaque at shorter wavelengths where the measured emissivity is influenced by the properties of the underlying metal surface. Theoretical predictions of the emsivity of a particulate layer were performed, and results are compared to the measured values. The theory adequately predicts the general features of spectral variation of the emissivity. The predicted trends in emissivity with particle size and deposit composition are also consistent with exerimental observations. Total (Planck-weighted) emissivities are calculated from the measured spectral values for the deposits at the tube temperatures. They increase with time from the clean tube value (0.2–0.3) to values typicals of deposits formed from western U.S. coal (0.45–0.55). Calculated total absorptivities are found to be lower than the correspoding emissivities.

Thermoluminescence dating of sediments older than ≈100 ka

For several years attempts have been made to establish reliable procedures for thermoluminescence (TL) dating of sediments older than ≈100 ka. Disagreement persists among TL workers about which procedures are reliable for which sediments. Two recent reports have demonstrated that TL ages up to ≈800 ka for polymineral, fine-silt loess and up to ≈600 ka for quartz from beach-dune sands agree well with expected ages. Several factors that apparently have influeneed negatively the accuracy of other results are: use of ultraviolet TL emissions; use of the regeneration TL procedures for feldspar-bearing samples: use of a single preheating procedure; and use of a peak-integration procedure rather than an equivalent-dose plateau test. Consideration of published data suggests that more attention should be paid to the variable emissions (intensity, glow curve shapes, signal lifetimes) from discrete grains within subsamples. The effects of such variability would probably account for the failure of peak-integration and single-preheating procedures to yield expected equivalent dose values. Single-grain (or micro-TL) studies of feldspar (and quartz) TL. both spectral emission and glow curve measurements, are recommended as aids to further understanding of current TL sediment dating practices.

Liquidus temperatures in the Ti-Al system

Liquidus temperatures were determined for the titanium-aluminum system at compositions ranging from 41 to 62 at. pct Al. The measurements were obtained by inducing solidification of slightly undercooled melts under containerless processing conditions using electromagnetic levitation. Absolute temperatures were determined by optical pyrometry in combination with independent measurements of spectral emissivities by laser polarimetry. The present liquidus temperatures are in agreement with two sets of literature values and are consistent with a set of solid-state literature data. These values exceed those selected in one recent proposed phase diagram revision by about 30 K and are as much as 40 to 60 K higher than those in another proposed revision.

Remote sensing of cloud, aerosol, and water vapor properties from the moderate resolution imaging spectrometer (MODIS)

The authors describe the status of MODIS-N and its companion instrument MODIS-T (tilt), a tiltable cross-track scanning spectrometer with 32 uniformly spaced channels between 0.410 and 0.875 mu m. They review the various methods being developed for the remote sensing of atmospheric properties using MODIS, placing primary emphasis on the principal atmospheric applications of determining the optical, microphysical, and physical properties of clouds and aerosol particles from spectral reflection and thermal emission measurements. In addition to cloud and aerosol properties, MODIS-N will be used for determining the total precipitable water vapor and atmospheric stability. The physical principles behind the determination of each of these atmospheric products are described, together with an example of their application to aircraft and/or satellite measurements. >

Normal spectral emittance of crystalline transition metal carbides

We report on experiments to determine the normal spectral emittance of crystalline forms of five transition metal carbides: hafnium carbide, niobium carbide, tantalum carbide, titanium carbide, and zirconium carbide. These emittance measurements were taken at the commonly used pyrometer wavelength of 0.65 μm. The specimens were cylindrical with 0.10-cm-diameter blackbody holes drilled axially to a depth of 1.0 cm. The crystalline specimens were prepared from sintered stock by floating zone arc refinement and then centerless ground to the desired diameter. Measurements were made in vacuum in the temperature range 1200&amp;lt;T&amp;lt;2400 K. The emittance of HfC tends to increase slightly with temperature (εHfC=0.4322+1.065×10−4 T) while those of NbC, TaC, TiC, and ZrC decrease (εNbC=0.4913−6.6×10−5 T, εTaC=0.4662−5.084×10−5 T, εTiC=0.8192−1.66×10−4 T, and εZrC=0.715−1.174×10−4 T). Bulk stoichiometries of the samples were C/Hf=0.86±0.03, C/Nb=0.833±0.014, C/Ta=0.79±0.05, C/Ti=0.955±0.005, and C/Zr=0.917±0.015. As a check on the accuracy of the method and procedure, normal spectral emittance measurements were taken on molybdenum yielding values consistent with those accepted. The normal spectral emittance was determined to be isotropic with respect to crystal orientation within the uncertainty of our measurements.

Investigation, comparison and improvement of technical infrared radiators

We investigated and compared relevant properties of technical infrared radiators, for example: foil radiators, quartz-tube and ceramic radiators. As typical representatives of the various radiator types we tested radiators by “Krelus Infrared”, Hirschthal, Switzerland, “Matherm”, Villars-les-Dombes, France, “Heraeus”, Kleinostheim F.R.G. and “Infrared International”, Ballydehob, Ireland. Special attention was paid to the determination of the spectral directional emissivities of the effective radiating areas of the infrared radiators. Our measurements were performed with an infrared spectrometer converted and adapted to spectral emissivity measurements. With this spectroscopic system we succeeded in measuring spectral directional emissivities of hot surfaces at temperatures from 973 to 1273 K between 1 and 16 μm wavelength with an accuracy of 2%. In order to perform the emissivity measurements, we constructed various models of blackbody-reference radiators. The quality of our final reference radiators was tested by comparing their normal spectral emissivity with the emissivity of two commercial blackbody-reference radiators. From comparative measurements and theoretical analysis of the spectral emissivity of blackbody cavities, we conclude that our reference radiators achieve a spectral emissivity better than 0.98 for wavelengths between 1 and 2 μm and better than 0.99 between 2 and 16 μm. In order to improve foil-type radiators, we developed ceramic-enamel layers for the protection of the foils against corrosive atmospheres without reducing their spectra emission. We succeeded with two different types of ceramic-enamel layers which can be applied to the “Krelus Infrared” foils, one of which is optically black. For the foils coated with each of the two enamels we found a long life time in the standard atmosphere. We assume also a good protection by these ceramic enamels against corrosive media. The “Krelus Infrared” foils coated with the optically black enamel exhibit similar spectral properties as the uncoated oxidized foils. An estimation of the quality of different infrared radiators is only possible with regard to a specific application and has to be performed, therefore, by the user of an infrared radiator. In addition to the determination of the fundamental radiator properties, this requires the consideration of the energy transfer within the entire radiator-sample system. We start by discussing its theoretical aspects. Subsequently, we present approximative solutions of particular energy-transport effects between radiator and sample for simple radiator-sample configurations. Special efforts have also been made to provide data for the energy transfer through air which is of importance for most radiator-sample systems. Of particular interest is the infrared transmittance along a path through the air between the radiator and the sample surface. Consequently, the transmittance of dry air was determined experimentally for pathlengths between 0.75 and 20.25 m. For these short pathlengths, comparisons of our measurements with “Lowtran” and “line-by-line“ calculations show a good agreement for spectral regions of strong CO 2 absorption.