| 摘要 |
PROBLEM TO BE SOLVED: To detect a signal having phase difference of 90 deg. from interference fringe well even if a luminous flux entering into a diffracting grating is not perfectly in parallel. SOLUTION: Assuming the wavelength of luminous flux isλ, the distance between a light emitting element 2 and the local position of an optical system 3 is d, the distance between the light emitting element 2 and the optical system 3 is f0 , the distance between the optical system 3 and an observation plane 9 is f2 , the pitch of a first diffraction grating isΛ1 , and the pitch of a second diffraction grating isΛ2 , the position of light receiving element 6-8 on the observation plane 9 is set as follows for an appropriate integer n; X=(2L0 <2> /nΛ0 ) 1-√[1-(2nΛ0 )<2> ]}, L0 =-f0 <2> /d+f2 ,Λ0 =1/2(-1/Λ1 +1/Λ2 ).
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