Patent ID: 6271916
Filing Date: 2001-08-07
Classification: G01N

Abstract:
An optical system for detecting contaminants and defects on a test surface comprising:a source of light to produce a beam;optics directing the beam along a path onto the test surface, producing an illuminated spot thereon;a detector detecting light; andan ellipsoidal mirrored surface, said mirrored surface and detector having an axis of symmetry about a line perpendicular to the test surface, said mirrored surface defining an input aperture positioned proximate to the test surface to receive scattered light therethrough from the surface and an exit aperture, said mirrored surface being substantially rotationally symmetric about said axis of symmetry, so that the mirrored surface reflects and focuses rotationally symmetrically about said axis of symmetry light that passes through the input aperture to the detector;said exit aperture being located opposite to the input aperture, said system further comprising:a lens assembly disposed between the input aperture and the exit aperture to collect light passing through the input aperture, defining collected light, said lens assembly focusing the collected light substantially at the detector, said detector providing a single output in response to the light focused to it by the mirrored surface and the lens assembly, such that orientation of contaminants and defects on the test surface does not affect detection.