Infrared Diffuse Reflectance Instrumentation and Standards at NIST
Leonard M. Hanssen, Simon G. Kaplan
A spectrophotometer system for spectral characterization of materials in the infrared has been built around a bench-top Fourier transform (FTIR) instrument. Its capabilities include the measurement of directional-hemispherical reflectance from 1 *m to 18 *m. The spectral reflectance measurement is performed with an integrating sphere with 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 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 of 2 *m to 18 *m. As part of the calibration procedure the spatial uniformity of the sphere throughput and the BRDF of the SRM material are evaluated.