| 摘要 |
PURPOSE:To enable a highly accurate measurement of a shape regardless of any relative variation in the measuring light by a method wherein a interfering light is divided into two light fluxes and projected onto an object to be measured rotating to compute a fine height and the position above the surface thereof. CONSTITUTION:Parallel laser light fluxes L1 and L2 polarized with a Kosters' prism 2 irradiates a video disc 6 through an optical system 3 to project two spots A and B. When there is any convex defect 14 on the disc 6, the spot B on the defect 14 is assigned to the observing point while the spot A to the reference point and respective reflected lights L3 and L4 are emitted from the prism 2 as interference light corresponding to the height of the defect 14 to be computed. On the other hand, the coordinate position of the defect is determined based on a signal from an encoder 8 for driving to rotate the disc 6. Thus, putting the reference point and the observing point on the object to be measured provides an interference signal high in the S/N ratio with a high resistance to vibrations and external noises thereby enabling a highly accurate measurement of the shape. |
