Infrared optical constants of black powders determined from reflection measurements

The real and imaginary parts of the complex index of refraction have been measured in the 3-14-microm region for nine black powders. Data were obtained from specular reflection measurements on pressed powder disks. A vintage prism spectrometer was considerably modified for this study. Polarized radiation, detected with a cooled photoconductor, was used to generate isoreflectance curves from which the optical properties were extracted. With the exception of a bone charcoal sample, the optical constants of the black powders exhibited no spectral features in the wavelength range considered. Measured values were generally in agreement with published data on similar materials. Surface effects were found not to produce a significant limitation on the results of our method.