| 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 reflective optical path of the object to be irradiated and providing a 90 deg. optical rotating element between a photodetector and this member. CONSTITUTION:The radiated light from a laser light source 21 is converged on the surface of a recording layer 26B through an optical system and a transparent protective layer 26A. The reflected light from this surface is made incident on a half prism 24 and is reflected by a prism surface 31. This reflected light passes a halfwave plate 33 and is made incident on a detecting prism 34 and is reflected by a reflecting face 35 and is received by a photodetector 36 having two-divided light reception areas 36A and 36B. In such a case, the reflected light from the recording layer 26B is elliptically polarized by an influence of the protective layer 26A, and p-polarized light and s-polarized light are mixed in the incident light to the prism 30, but almost all s- polarized light is reflected by the surface 31. This s-polarized light has the plane of polarization rotated at 90 deg. by the plate 33 and is made incident on the face 35 as p-polarized light. Consequently, the detection sensitivity is not degraded though s-polarized light is included in the incident luminous flux to the prism 30, and the in-focus state is stably detected with a high precision. |
