| 摘要 |
PURPOSE:To always stably detect the in-focus state with high precision without having influence upon birefringence of an object to be irradiated by providing a prescribed reflecting member in the optical path of reflected light from the object, and providing a 90 deg. optical rotation element between the reflecting member and the object. CONSTITUTION:The radiated light from a laser light source 21 is condensed on the surface of a recording layer 26B through an optical system and a transparent protective layer 26A. The reflected light from the surface is made incident on a half prism 24, and the reflected light (the intensity is independent upon polarization) is made incident on a detecting prism 30 and is reflected by a prism surface 31. In such a case, since a halfwave plate 32 is so arranged that a half of the luminous flux 33 made incident on the prism 30 is transmitted through, the luminous flux transmitted through the plate 32 and the luminous flux not transmitted there which have the same quantity of light are made incident on the prism 30. These luminous fluxes are reflected by the surface 31 and are received by a photodetector 34 having two-divided light reception areas 34A and 34B. The quantity of light after reflection on the prism 30 is not dependent upon polarization of the incident luminous flux and is fixed. Consequently, the in-focus state is stably detected with a high precision without an influence of retardation of the protective layer 26A. |
