| 摘要 |
PROBLEM TO BE SOLVED: To simplify the alignment work and to provide a length measuring device in which no shifting of alignment occurs by constituting a reflection target of a corner prism and providing a small corner prism for receiving a reflected light and reflecting an incident light on the same optical path in the vicinity of an interference gauge. SOLUTION: A corner prism 18 is provided on the lower side of the 1/4λplate 16 of the prism part of a polarizing beam splitter 12, a corner prism 4 is provided in the upper part of a traveling object 3 and small corner prism 20 is provided on the upper front face of a housing. A reference light is reflected by the polarizing beam splitter 12, reflected by the prism 18 after passing through the 1/4λplate 16, passed through 1/4λplate 16 again and made incident on the polarizing beam splitter 12. A measuring light is made incident on the prism 4 after passing through the 1/4λplate 16. A reflected light from the prism 4 is reflected by the prism 20 and made incident again on the polarizing beam splitter 12 after being sent on the same optical path. The measuring light is made to interfere with the reference light and received by a length measuring optical system 5.
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