OFF-AXIS LIGHT BEAM DEFECT DETECTOR

摘要

The appts. detects a property such as a defect in a surface to be scanned. A focusing or objective lens is provided together with a subsystem for maintaining a fixed distance between the focusing lens and the scanned surface. Scanning is effected by providing lateral movement between the lens and the surface. An off-axis light beam source is provided having a beam of light which is directed to pass through the lens to the scanned surface. A light beam-sensing element is positioned so as to detect the portion of the light beam reflected from the surface and transmitted back through the lens.