| 摘要 |
PURPOSE:To measure a length with high accuracy without generating an error even if inclination is generated in a machine apparatus to be measured, by monitoring the image of the interference fringe pattern shape in interference light beam formed by the interference of reference beam and reflected beam. CONSTITUTION:The beam emitted from a beam source 1 is enlarged in its diameter by a collimator lens 2 to be split into two directions by a beam splitter 3 and the split beams are respectively condensed onto a reference mirror 8 and a reflecting mirror 9 by objective lesses 6, 7. Next, the reflected beams from the mirrors 8, 9 are synthesized by the splitter 3 to interfere mutually and an interference fringe pattern is formed into an image on a multiple picture element beam receiving element 11 and this image is displayed on a monitor TV12. At this time, if the beam of the beam source 1 consists of polarized beam having a vibration direction parallel to an incident surface and plane-polarized beam crossing said polarized beam at a right angle, using a polarizing type splitter as a splitter 3, and putting lambda/4 plates (lambda is wavelength) 4, 7 in each optical path, the reflected beams from the mirrors 8, 9 are guided to the element 11. If either one of the mirrors 8,9 is inclined by a minute angle with respect to an optical axis, interference fringe patterns can be displayed at an equal interval.
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