| 摘要 |
PURPOSE:To perform a measurement by a light beat free from moving speed limit, by using one of first and second beat signals detected with a detector switching according to the situation. CONSTITUTION:One of two sets of light beats are detected with a detector 10 while the other with a detector 11. Then, a light beat signal which is obtained by splitting a part of incident light with a beam splitter 8 and combining two polarized lights with a polarizer 9 is detected with a detector 14 to obtain a signal with the frequency of f1-f2 as reference signal and the frequency difference between said two sets of light beat signals and the reference signal is determined with frequency difference counters 12 and 13. Then, counts of the counter 12 or 13 are adopted selectively according to the direction of a moving mirror 4 moves or a switching over is done between the output signal of the detector 10 and the output signal of the detector 11 and the frequency difference between the output signal and the reference signal is counted with one frequency difference counter thereby enabling the measuring of length by a light beat free from moving speed limit.
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