| 摘要 |
PURPOSE:To accurately measure even the local speed distribution of a body to be measured by using a low coherence light source as a light source and providing an optical path length adjusting means which makes a difference in optical path length between two irradiating light beams. CONSTITUTION:The low coherence light source which has a coherence length of several to tens of micrometers is used. If there is a plane where two irradiating light beams are equal in optical path length in the crossing area, the measurable area 22 is a very limited area which is near by the plane of equal optical path length in the crossing area and corresponds to the coherence length. When there is no measurable area 22 in the crossing area 7, or when the area is large even if it is present, the optical path length difference adjusting means 21 adjusts the optical path length difference between the two irradiating light beams to set a small localized area as the measurable area 22. The optical path length difference adjusting means 21 stores a mirror 3 and a lens 5 on a mobile table and varies the distance between a beam splitter 2 and the mirror 3. |
