| 摘要 |
PURPOSE:To improve resolving power for measuring length by disposing a quarter-wave plate between a composite prism which reflects two split beams by a plural number of times between two plane reflection mirrors and makes the same incident to a synthetic optical system and the plane reflection mirrors. CONSTITUTION:Laser incident light 1 is split to two parallel beams 2, 2 by a beam splitter (BS). The split beams are repeatedly reflected via a lambda/4 plate 13 between the respective faces in a composite prism 12 having reflection faces 26, 27 intersecting orthogonally with each other and plane mirrors 14, 15 in the sequence shown by the numbers in round circles. The inclination with the mirrors 14, 15 is absorbed by the reflections and the beams 29, 29 passing the same optical path as the optical path of incident light 2, 2 are emitted. The emitted beams are again made incident to the BS11 by which the beams are combined to exit light 30 parallel with the light 1. Since the plate 13 rotates 90 deg. the plane of polarization of the reflected light twice before and after by the plate 13, the loss of the light in the optical path is hardly generated. The length of the optical path is increased by multiplexing the optical path and the resolving power for measuring length is improved. |
