Particles are distinguished from pits, voids, scratches, and other subsurface defects in a surface of a substrate by impinging the defect with polarized light and integrating light scattered by the defect over a wide angular range to produce a total integrated response. Using a P-polarized...http://www.google.ca/patents/US6169601?utm_source=gb-gplus-sharePatent US6169601 - Method and apparatus for distinguishing particles from subsurface defects on a substrate using polarized light 
