Measurements and predictions of light scattering by clear coatings

Comparisons are made between calculated and measured angle-resolved light-scattering distributions from clear dielectric isotropic epoxy coatings over a range of rms roughness conditions, resulting in strongly specular scattering to diffuse scattering characteristics. Calculated distributions are derived from topography measurements performed with interferometric microscopes. Two methods of calculation are used. One determines the intensity of scattered light waves with a phase integral in the Kirchhoff approximation. The other is based on the reflection of light rays by locally flat surfaces. The angle-resolved scattering distributions for the coatings are measured with the spectral trifunction automated reference reflectometer (STARR) developed by the National Institute of Standards and Technology. Comparisons between measured and calculated results are shown for three surfaces with rms roughness values of approximately 3, 150, and 800 nm for an angle of incidence of 20 degrees.