Infrared diffuse reflectance instrumentation and standards at NIST |
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Authors: | Leonard M Hanssen Simon Kaplan |
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Institution: | Optical Technology Division, NIST Gaithersburg, MD 20899 USA |
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Abstract: | A spectrophotometer system for spectral characterization of materials in the infrared has been built around a bench-top Fourier transform instrument. Its capabilities include the measurement of directional-hemispherical reflectance from 1 to 18 μm. The spectral reflectance measurement is performed with an integrating sphere with an incidence angle of 8°. Both relative and absolute measurements can be made. Several methods can be used to determine the absolute value of the directional-hemispherical reflectance of samples. The primary method used is independent of the integrating sphere theory and the requisite assumptions associated with its use. The calibration of a standard reference material (SRM) is described. This SRM has a reflectance value near 0.9 over the complete calibration range 2–18 μm. As part of the calibration procedure the spatial uniformity of the sphere throughput and the bi-directional reflectance distribution function (BRDF) of the SRM material are evaluated. |
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Keywords: | Infrared Spectral reflectance Directional-hemispherical reflectance Diffuse reflectance Integrating sphere |
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