| 摘要 |
PURPOSE:To execute the detection with high sensitivity and with high precision by constituting the subject device so that a luminous flux reflected by the surface of a target object becomes a convergent light, its half is allowed to transmit through a phase element and an interference light by a convergent light which does not transmit through the phase element is photodetected. CONSTITUTION:A light source 1 irradiates a laser beam to a plate beam splitter 2. A condensing lens 3 converges a luminous flux reflected by the splitter 2 onto the surface 5 of a target object, and converges a reflected luminous flux from the object surface 5. A dielectric thin film (phase element) 6 is vapor-deposited and formed in a half area by setting the center of the luminous flux as a boundary on the back side of a substrate of the splitter 2. A phase of the light beam is delayed by pi by comparing the case a light beam passes through the thin film 6 with the case it does not pass through. A photodetector 4 is divided into two photodetecting areas, and constituted so that the optical intensity corresponding to each crest can be detected in each photodetecting area, in a position in which diffracted light intensity distributions of two crests become equal when a distance between the lens 3 and the object surface 5 is in a prescribed distance. Accordingly, a distance of the object surface 5 can be detected from a variation of the optical intensity in two photodetecting areas. |
