| 摘要 |
PROBLEM TO BE SOLVED: To make a flat object surface possible to be scanned without changing the optical travel of measurement rays by allowing the scanning ray travel to run telecentrically on the side of an object to be scanned, and preventing the travel from being affected by the frequency modulation of the output signal of an interferometer which is caused through surplus scanning. SOLUTION: Coherent parallel rays 2 radiated from a light source 1 are branched to reference rays 4 and measurement rays 6 by a split mirror 3 of the Michaelson interferometer. The reference rays 4 pass through a crystal glass block 18, is diffracted with the advance/retreat movement in the Bragg diffraction grating, is subjected to Doppler deviation, and enters a reference mirror 5. Then, the measurement rays 6 enter bear scanning mirrors 7' and 7" where rotary axes orthogonally cross each other, and an object side telecentric ray process can be obtained, and is focused on an object side focusing surface 22' by a convergence lens system 8. In this case, the optical travel is equal in length from a focal point 21 to the object side focusing surface 22'. Therefore, the optical travel of the measurement rays 6 does not change, thus preventing any unnecessary frequency modulation from occurring in an interferometer signal.
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