Optical system, detector and method for detecting peripheral surface defect of translucent disk

摘要

Defect in a edge portion of a disk is detected by irradiating a inspected region of an outer peripheral surface with light beam spot through an inside portion of the disk and receiving scattered light from the inspected region by means of a first light receiving system provided externally of the disk in a vicinity of the inspected region. Therefore, there is substantially no scattered light from alien attached externally of the disk.