Light scattering investigation of the nature of polished glass surfaces

Light scattering from a rough surface is approached by a vectorial method applying the Lorentz reciprocity principle. The derived theory rediscovers the fact, already pointed out by Rayleigh, that the scattered field vanishes for p-polarisation at a scattering angle depending on the refractive index of the illuminated material. Moreover it also gives an easy interpretation for the discrepancy generally observed between the measured values and those computed from the simplified theory. Experimental indicatrices of the light scattered from polished glass surfaces lead to a surface index of refraction which is much lower than the bulk index of silicate glasses, but nearer to the bulk index of silica free glasses. This result is consistent with the assumption, derived from other experiments, that a polished silicate glass surface is coated with a thin silica film.