| 摘要 |
PURPOSE:To detect a center position with high precision in a simple structure, by irradiating the boundary part between the part, where an information track is formed, and the part, where it is not formed, on a substrate with a light having a certain area to detect the quantity or the shape of the diffracted light. CONSTITUTION:A disc 4 of a detection object is attached onto a stage 2. When a light source 8 in a dark box 7 is lit, the lihgt from the light source 8 is irradiated to a boundary 12 between an informstion track 5 and a flat part 6 of the disc 4 as a uniform light having a certain area through a lens 9, a pinhole 10, and a lens 11. A diffracted light 13 is detected by a photodetector 14 to detect the center position of the disc 4. |
