| 摘要 |
PROBLEM TO BE SOLVED: To minimize the influence of leak light between the polarization components of a polarization beam splitter. SOLUTION: Laser light separated with a non-polarization beam splitter 42 extracts the same frequency component as the leak light produced in the transmittance of a polarization beam splitter 43 by passing a straight line polarizer 55. Next, the polarization azimuth is adjusted by a half wavelength plate 56 in the same direction as the polarization azimuth of the leak light of the polarization beam splitter 43. Furthermore, intensity is regulated with a variable intensity filter 58, and composited to a reference light path with a half mirror 44. Then, measuring light is blocked by a means such as a light shielding plate 46, and an error beat due to the leak light included in the reference light is observed with a photodetector 52. The optical path length of correction light is changed by regulating a measuring stage 60 putting a mirror 59 and the half mirror 44 so that an error beat signal is minimum to change a phase so as to regulate the variable intensity filter 58 so that the error beat is minimum. In this state, the shielding plate 46 of the measuring light blocked previously is measured to be removed from the optical path.
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