Characterization of highly absorbing black appliques in the infrared

Angular and polarimetric directional hemispherical reflectance (DHR) measurements of three highly absorbing appliques in the 2.5-14.3-mum IR spectral region are presented. In addition, scanning electron microscopy (SEM) images are presented to probe the surface morphology of these appliques. DHR measurements of Energy Science Laboratory, Incorporated (ESLI), Rippey, and Rodel appliques were obtained at incidence angles of 8 degrees, 30 degrees, and 50 degrees and as a function of S, P, and unpolarized incident light. The ESLI applique exhibited the lowest DHR for all angles and incident polarization states. SEM images revealed a fibrous structure for the ESLI applique with fiber diameters of the order of 7-8 mum, whereas the Rippey and the Rodel appliques showed spongelike surfaces with pore diameters of 40-50 and 30-40 mum, respectively. All the appliques use cavities or fibers in conjunction with carbon compounds to absorb IR radiation. The optical system designed to perform these measurements, a method for correcting off-normal DHR measurements in center-mount integrating spheres, and sources of measurement error are also discussed.