| 摘要 |
PURPOSE:To remove the unstabilization of an optical spot position or light intensity distribution due to a change in the optical axis of an objective lens by reflecting objective lens inclination detecting light by an optical thin film formed on one side of the objective lens and detecting the reflected light by an objective lens inclination detecting means. CONSTITUTION:The objective lens 10 is coated with a half reflecting face optical thin film 11 having a property for transmitting the wavelength of focus exposing light (a) and reflecting the wavelength of an objective lens inclination detecting light (b). Thereby, the light (b) is reflected by the half reflecting face 11, converged by a condensor lens 14 and led into a 4-divided photodetecting element 15. When the optical axis of the objective lens 10 is inclined by theta from the optical axis 19 of the incident light, the reflected objective lens inclination detecting light (b) is turned to a reflected light axis 20 inclined by the shear of the curvature center of the face 11, so that the inclined state can be detected from the difference of photodetecting values. Consequently, the position of an optical spot or light intensity distribution can always be stabilized. |
