| 摘要 |
PURPOSE:To ensure an inspection of a disk by setting a sensor so as to detect just either one of diffracted beams of the primary or higher orders generated from a signal track and detecting only the signal corresponding to a defect on the disk recording surface. CONSTITUTION:When the laser light is projected to a disk 1, the diffracted light is emitted due to a defect and a track on the disk surface. If the recording surface has no defect, the laser light 11 projected to the disk 1 produces diffracted beams 13 and 14 at the prescribed angle positions by the track on the disk recording surface in addition to the positive reflected light 12. While no diffraction phenomenon is produced due to the track if the track has a partial crack owing to the defect of the recording surface. In other words, the beams 13 and 14 are modulated in response to the crack state of the track and generate the diffracted light 15. Thus the change of a diffraction phenomenon can be detected by setting a sensor 9 on the optical axis of the beam 13. Furthermore, it is possible to provide a sensor corresponding to the diffracted beam of higher order. |
