Validation of the Infrared Emittance Characterization of Materials Through Intercomparison of Direct and Indirect Methods |
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Authors: | Leonard M Hanssen Sergey N Mekhontsev Vladimir B Khromchenko |
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Affiliation: | (1) Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, U.S.A. |
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Abstract: | A comparison of the spectral directional emittance of samples as a function of wavelength was performed at the Fourier Transform
Infrared Spectrophotometry (FTIS) and the Advanced Infrared Radiometry and Imaging (AIRI) facilities at NIST. At the FTIS,
the emittance is obtained indirectly through the measurement of near-normal directional-hemispherical reflectance (DHR) using
an infrared integrating sphere. At the AIRI, the normal directional emittance is obtained directly through the measurement
of the sample spectral radiance referenced to that from blackbody sources, while the sample is located behind a black plate
of known temperature and emittance. On the same setup at the AIRI, the normal emittance at near ambient temperatures is also
measured indirectly by a “two-temperature” method in which the sample spectral radiance is measured while the background temperature
is controlled and varied. The sample emittance measurements on the comparison samples are presented over a wavelength range
of 3.4 μm to 13.5 μm at several near-ambient temperatures and for near-normal incidence. The results obtained validate the
two independent capabilities and demonstrate the potential of the controlled background methods for measurements of the radiative
properties of IR materials. |
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