| 摘要 |
PURPOSE:To eliminate the formation of an abnormal image due to reflected light from a photodetecting element for synchronous detection with simple constitution by arranging the photodetection formation surface of the photodetecting element slantingly to a plane crossing an incident laser beam at right angles so that the light beam traces a route which does not reach the image formation surface. CONSTITUTION:The photodetecting element 13 is fitted having its reverse surface in contact with a photodetecting element fitting surface 15 provided in a cylindrical photodetection part support member 14, and a cylindrical lens 17 is provided on the front end surface of the cylinder part of the photodetection part support member 14 in front of the photodetecting element 13 across a housing 16 for cutting off external light. The photodetecting element fitting surface 15 is provided slanting from the plane perpendicular to the incidence direction of the laser beam 2a for synchronous detection and the photodetection surface of the photodetecting element 13 fitted having its reverse surface in contact with said surface also slants from the plane perpendicular to the incident light of the laser beam 2a, so that reflected light is reflected by the photodetection surface as some angle to the incident light 2a shown by a broken line 19. The photodetection part support member 14 is fitted at such a position that the reflected light 19 is not incident on a mirror for synchronous detection, etc.
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