Infrared diffuse reflectance instrumentation and standards at NIST
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.
- Publication:
-
Analytica Chimica Acta
- Pub Date:
- 1999
- DOI:
- 10.1016/S0003-2670(98)00669-2
- Bibcode:
- 1999AcAC..380..289H
- Keywords:
-
- Infrared;
- Spectral reflectance;
- Directional-hemispherical reflectance;
- Diffuse reflectance;
- Integrating sphere