| 摘要 |
PURPOSE:To remove a nonlinear error caused by the effect of the leaking light generated in a polarization separating element by making a plurality of luminous fluxes having the different frequencies interfere through a material to be measured, and forming a optical beat signal. CONSTITUTION:The lights (frequencies f1 and f2) in the polarized state, which are intersecting at a right angle, from a laser 1, are divided into two parts with a beam splitter(BS) and further divided into two parts with a BS3. The lights transmitted through the BSs2 and 3 interfere with each other in a polarizing plate 4, and converted into the reference beat signal with a sensor 5. The lights reflected from the BSs2 and 3 are divided into two parts of the light of the frequency f1, which is transmitted through the polarized light BS (PBS) 9, and the light of the frequency f2 reflected from the BS9. The light of the frequency f1 is reflected from a mirror 13 (material to be measured) and cast into the PBS 9. Thus, the lights of the frequencies f1 and f2 interfere with each other in the polarizing plate 14 through the same optical paths and become the measurement beat signal with the sensors 8 and 15. An operator 18 operates the displacement amount of the mirror 13 based on the outputs of phase- difference meters 16 and 17. The result of the operation is displayed on a display device 19.
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