| 摘要 |
[PROBLEMS] To perform highly accurate focus control in an optical recording medium of multilayer structure having an interface of each layer with a reflectance reduced as much as possible. [SOLVING ELEMENT] In a focus control apparatus with optical pickup for use in an optical recording medium of multilayer structure, laser light irradiating device including a laser light source (50) and an objective lens (54) irradiates laser light to an optical recording medium (D), a photodetector (55) detects an optical characteristic change associated with multiphoton absorption caused when the laser light is condensed to at least one of recording layers, and in accordance with the detection result, focus control in the optical pickup is performed for an arbitrary recording layer (L1 to Ln). |
