| 摘要 |
In a displacement detecting device, an objective lens condenses the outgoing light coming from a light source toward a surface-to-be-measured. The optical path of the reflected light coming from the surface-to-be-measured is separated from the optical path of the outgoing light coming from the light source by a separation optical system. The reflected light passing through the separation optical system is condensed by a collimator lens and has astigmatism generated therein by an astigmatism generator, and the reflected light in such a state is incident on a light receiving section. A position information generator generates the position information of the surface-to-be-measured using a focus error signal obtained based on the amount of light detected by the light receiving section. Further, the position of the condenser, the astigmatism generator or the light receiving section in the optical axis is set so that the value of the focus error signal is equal to “0” when the focus of the outgoing light condensed by the objective lens is located on the front side or back side of the surface-to-be-measured. |
