| 摘要 |
PURPOSE:To accurately measure the displacement quantity of the reflecting surface of, for example, an optical disk covered with a transparent layer without being affected by a transparent layer by setting the angle of incidence upon the surface of the transparent layer to the Brewster angle of the transparent layer. CONSTITUTION:Laser light LA 1 emitted by a light source 3 passes through a polarizing plate 5 to become a P polarized parallel light beam, which is incident on the optical disk 1 at an angle theta of incidence. When the angle theta is set to the Brewster angle of the transparent layer 2, the light LA 1 is not reflected by the layer 2, but enters the layer 2 and is reflected by the reflecting surface 1f. Its reflected light LA 2 is incident on a condenser lens 6 with focal distance (f). (A photodetecting element 7 composed of, for example, a two-dimensional image sensor arranged in the direction as shown by an arrow (x) is provided at the focus position of the lens 6 so that the photodetection surface is perpendicular to the optical axis. If the surface 1f slants by a fine angle delta, the light LA 2 slants by the angle 2delta, the spot position of incidence on the element 7 shifts. The element 7 sends out its (x)-directional and (y)-directional outputs which vary according to the displacement quantity of the element 7. Those measured values, distance (f), and angle theta are used to find the angle delta. |
