Among all known materials, we found that a forest of vertically aligned single-walled carbon nanotubes behaves most similarly to a black body, a theoretical material that absorbs all incident light. A requirement for an object to behave as a black body is to perfectly absorb light of all wavelengths. This important feature has not been observed for real materials because materials intrinsically have specific absorption bands because of their structure and composition. We found a material that can absorb light almost perfectly across a very wide spectral range (0.2-200 m). We attribute this black body behavior to stem from the sparseness and imperfect alignment of the vertical single-walled carbon nanotubes.absorbance ͉ emissivity ͉ reflectance A black body is a theoretical object that absorbs all light that falls on it, because no light is transmitted or reflected (1). As a result, it appears perfectly black at room temperature and is the most efficient thermal absorber and emitter because any object at thermal equilibrium will emit the same amount of light as it absorbs at every wavelength. The radiation spectrum of a black body is determined solely by the temperature and not by the material, properties, and structure. These features, as an ideal source to emit or absorb radiation, make the black body valuable for many applications. For example, because the black body efficiently converts light to heat, it has great importance to solar energy collectors (2-5) and infrared thermal detectors, such as pyroelectric sensors (6-8). As a perfect emitter of radiation, a hot material with black body behavior would create an efficient infrared heater and would be valuable for heat liberation (9), particularly in space or in a vacuum where convective cooling is negligible.A requirement for an object to behave as a black body is that it perfectly absorbs light of all wavelengths; yet, in reality, black bodies do not exist. Emissivity is a measure of how similar an object is to a black body and is defined as the ratio of the energy radiated by that object and by a black body. Therefore, a black body would possess emissivity of unity for all wavelengths. This important feature has not been observed for real materials because materials intrinsically have specific absorption bands because of their structure and composition, and thus, the emissivity of any real object is less than unity and is wavelength dependent.A good approximation of a black body is a cavity; however, this structure limits its utility. A material exhibiting black body behavior would solve this structural limitation and increase its practical usefulness. Hence, various processes and materials have been developed to blacken the surface by chemical treatment (10, 11), plating (4-6), and painting (8). Despite these efforts, emissivities for black coatings (Astro Black), chemically treated black surfaces (Hino Black), and microscale needle-like structure of nickel-phosphorus alloy (Anritsu Black) can be as high as 0.96 at 5-9 m but decreases notably at Ͼ9 m (Fig...

Below the freezing point of silver, radiation thermometers are generally calibrated by implementing the multi-point interpolation method using blackbody measurements at three or more calibration points, rather than the ITS-90 extrapolation technique. The interpolation method eliminates the need to measure the spectral responsivity and provides greater accuracy at the longer wavelengths required below the silver point. This article identifies all the sources of uncertainty associated with the interpolation method, in particular, those related to the reference blackbody temperatures (either variable-temperature or fixed-point blackbodies) and to the measured thermometer signals at these points. Estimates are given of the 'normal' and 'best' uncertainties currently achievable. A model of the thermometer response is used to propagate all the uncertainties at the reference points and provide a total uncertainty at any temperature within the calibration range. The multi-point method has the effect of constraining the total uncertainty over this range, unlike the ITS-90 technique for which the uncertainties propagate as T 2 . This article is a joint effort of the working group on radiation thermometry of the Consultative Committee for Thermometry (CCT), summarizing the knowledge and experience of all experts in this field.

A Fourier transform infrared (FTIR) spectrometer was developed to measure spectral radiance of thermal-infrared emission near ambient temperatures with high accuracy at the NMIJ (former NRLM). The spectrometer uses a simple Michelson interferometer that consists of corner cube mirrors and a KBr beam splitter. The spectral range between 5 µm and 12 µm was covered by a liquid nitrogen cooled photovoltaic HgCdTe detector operated in the photoamperic mode. Opaque solid samples with good thermal conductivity were heated directly by the thermostatic fluid up to 100 °C. To reduce the effect of absorption by air, all of the optical components were operated in the vacuum. The spectrometer was calibrated against two high quality reference blackbodies: a fixed-temperature blackbody cooled by liquid nitrogen and a variable-temperature blackbody operated in the temperature range between -20 °C and 100 °C. We measured the normal spectral emissivity of alumina ceramic samples and determined the uncertainties. The combined standard relative uncertainties for the alumina samples at 100 °C was smaller than 1% when the emissivity was close to unity, and less than 3% when the emissivity was approximately 0.2.

The nonlinearity characteristics of photoconductive and photovoltaic HgCdTe detectors were experimentally investigated in the infrared wavelength region by use of the National Physical Laboratory detector linearity measurement facility. The nonlinearity of photoconductive HgCdTe detectors was shown to be a function of irradiance rather than the total radiant power incident on the detector. Photoconductive HgCdTe detectors supplied by different vendors were shown to have similar linearity characteristics for wavelengths around 10 microm. However, the nonlinearity of response of a photovoltaic HgCdTe detector was shown to be significantly lower than the corresponding value for photoconductive HgCdTe detectors at the same wavelength.

No abstract