Determination of light-scattering properties of glass surfaces

Glass surfaces were damaged in a defined manner by sandblasting with an adjustable sand blasting machine and subsequent etching with HF. Investigations with the scanning electron microscope (SEM) showed surface defects with an ellipsoidal shape. A quantitative evaluation of the exact profile of these defects was made using mathematical evaluation of stereographic pairs. A new method is described for characterizing surfaces with optical light scattering. In contrast to the usual method of a fixed specimen and a photocell moving on a circle around it, here the specimen revolves on an axis perpendicular to a laser beam and rotates on an axis parallel to it in order to average the scattering over a large area of the surface, thus preventing interferences of the coherent laser beam with surface defects. A theory is described which enables a numerical estimation of roughness parameters using a distribution function of angles of small mirrors to the average surface. In this special case the theory was extended for the special type of defects having an ellipsoidal shape. The results are discussed with respect to creation of surface defects by sandblasting, which are accompanied by subsurface cracks.