DISK INSPECTING DEVICE

摘要

PURPOSE:To perform assuredly an inspection of a disk by scanning the recording surface with the laser light to detect the zero order diffracted light and the primary diffracted light by each independent sensor from the laser light reflected from the disk surface, and detecting only the signal corresponding to a defect on the disk recording surface. CONSTITUTION:The laser light given from a laser light source 5 scans swirlingly a surface to be inspected of a disk 1. The laser light projected to the disk 1 is diffracted by a defect and a track on the disk surface and detected by sensors 8 and 10. The outputs of both sensors contain the signal corresponding to the defect and the variance component of diffraction conditions due to the track. The primary diffracted light output detected by the sensor 10 is controlled in amplitude and inverted in phase by a phase inversion amplifier 11 and at the same time applied to an adder 12 together with the zero-order diffracted light output detected by the sensor 8. The variance components of diffraction conditions produces a 180 deg. phase difference between the zero-order primary diffracted beams, therefore cancelled by the adder 12. Then a diffracted light output produced due to a defect on the disk is detected at the output of the adder 12.