| 摘要 |
PURPOSE:To prevent the creeping of optically detected signals from occurring by slantingly placing the detection surface of an optical detection element in the direction opposite to the joint surface of a Wollaston prism and avoiding the overlap of at least three reflected beams. CONSTITUTION:The optical detection element 23 is arranged in the direction opposite to a joint surface 18c of the Wollaston prism 18 with a prescribed slant angle. In this case, the differences among the intensity distributions of reflected light beams R0, R1 and R2 become small and the shapes of the reflected beams R1 and R2 formed on both sides of light receiving elements 23b and 23c become approximately a circular shape in terms of an effective intensity level L0, thereby respective reflected beams R0, R1 and R2 are not overlapped with each other. Moreover, by tilting light receiving elements 23a or 23c, the creeping of optically detected signals is prevented from occurring, and desired signals are obtained, so that beams reflected on the surface of the light receiving elements do not return to word an objective lens 11 as a stray light beam. |
