| 摘要 |
PURPOSE:To prevent light from being reflected to a photodetector group by a surface which faces the photodetector group, by providing the facing surface outside of a vacuum area. CONSTITUTION:A glass window 9 is placed at the opposite position to photodetector groups 6a, 6b-6e, and is fixed with a flange 10 to produce a vacuum internally. Further, a reflected-light preventing cover 11 whose internal wall is blackened is provided at the outside of the flange 9. consequently, light emitted from a beam 1 to the glass window 9 passes through the glass window 9 to reach said cover 11. The cover 11 is set at the outside of the vacuum area, so the internal wall is blackened easily and the position of the opposite surface is set easily, thereby preventing the reflection of light to the photodetector groups 6a, 6b-6e easily. |
