| 摘要 |
PROBLEM TO BE SOLVED: To detect an accurate angular position by condensing a weak recursive laser beam. SOLUTION: A reflection mirror 5 provided, tilted 45 deg., on the projection optical axis of a projection laser beam projected from a laser oscillator 4, a total-reflection rotary mirror 3 which is, tilted 45 deg. relative to the projection optical axis, provided for free rotation around the projection optical axis, a rotary encoder 17 for detecting the rotational angle of the rotary mirror 3, a light receiving element 7 wherein a recursive laser beam reflected on a recursive reflective body R is reflected on the total-reflection rotary mirror 3 and the reflection mirror 5 and then received, and a counter 9 for detecting the angular position of the recursive reflective body R with the signal of the light- receiving element 7 and the rotary encoder 17, are provided. Here, the reflection mirror 5 is provided with a half mirror part 5a of high transmissivity at its central part while a total-reflection mirror part 5b of low transmissivity is formed at its outer peripheral part.
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