Specular Reflectance of Aluminized Ground Glass and the Height Distribution of Surface Irregularities

The relative specular reflectance of various aluminized ground-glass surfaces has been measured at normal incidence. All of the samples tested had a Gaussian reflectance curve except for the most finely ground surfaces which could be prepared. Since the observed reflectance always became negligible at sufficiently short wavelengths, recent theoretical results could be used to determine the height distribution of the surface irregularities directly from the specular reflectance data. In most cases it was Gaussian. Since the specular reflectance of aluminized ground glass falls off very nearly exponentially with decreasing wavelength, the exponent being proportional to 1/λ2, scatter plates of this material make excellent reflection filters with very good rejection characteristics and little decrease in the energy passed in the desired wavelength region. The limiting wavelength for appreciable specular reflection at normal incidence is roughly 14 of the average particle size of the grinding powder used, so that these scatter plates can be designed for use not only in the far infrared but also at shorter wavelengths extending nearly to the visible region of the spectrum.