| 摘要 |
PROBLEM TO BE SOLVED: To prevent deterioration of a focusing signal incident to wavelength multiplexing, to secure a signal level larger than a fluorescent signal, and to detect a focusing signal and a tracking signal of high S/N ratio. SOLUTION: A focusing error signal is formed based on return light from a first or a second substance through a first detecting system 20; and then, difference is determined at zero crossing position of the focusing error signal observed in this first detecting system 20 and a second detection system 21, and the difference is added to the focusing error signal observed in the second detecting system 21, thereby correcting a focusing position by a focusing servo. As a result, a light beam is controlled so as to focus at the position where fluorescence has the maximum color development. Using a reflected light beam of light from a light source at the boundary surface, deterioration of the focusing signal incident to wavelength multiplexing can be prevented, enabling a signal level to be secured that is larger than the one with the focusing signal formed by a fluorescent component, and enabling focus control of high S/N ratio. |
