The Far Infrared Reflectance of Optical Black Coatings

Abstract

Far infrared specular reflectance spectra of six optically black coatings near normal incidence are presented. The spectra were obtained using 9 bandpass transmission filters in the wavelength range between 12 and 300 microns. Data on the construction, thickness, and rms surface roughness of the coatings are also presented. The chemical composition of two coatings can be distinguished from that of the others by a strong absorption feature between 20 and 40 microns which is attributed to amorphous silicate material. Inverse relationships between these spectra and coating roughness and thickness are noted and lead to development of a single reflecting-layer model for the measured reflectance. The model is applied to the spectra of several coatings whose construction falls within its constraints.