| 摘要 |
PURPOSE:To improve defect detection sensitivity by receiving scattered and reflected light by a convex lens arranged 1-2 times as far away from an position to be irradiated as the focal length and arranging an end surface of an optical fiber connecting with a scattered and reflected light detecting means closer to the lens than an image formation point within a range where there is no loss of the quantity of photodetection. CONSTITUTION:When the distance (a) between the position P to be irradiated (scanned) and the principal point H of the convex lens 2 is set, for example, 1.5 times as long as the focal length (f) of the lens 2, the distance (b) from the principal point H of the lens 2 to the image formation point B is about three times as long as the focal length (f), i.e., twice as long as the distance (a). An angle beta of incidence on the end surface of the optical fiber 3 is about a half as large as the angle alpha of photodetection of the lens 2. Consequently, the majority of light incident on the optical fiber 3 is transmitted efficiently to a photodetecting element while reflected totally by the boundary surface between the core and sheath. Further, the end surface of the optical fiber 3 is arranged delta closer to the lens 2 than the image formation point B. Thus, the holder part of the optical fiber 3 serves a a slit to reduce stray light and also reduce noise components. |
