| 摘要 |
PURPOSE:To measure the irregularities of a surface to be checked accurately with interference fringes, by providing image forming lenses on a light path between a second diffraction grating and a hologram screen, and providing the image forming relation of a equal multiplication. CONSTITUTION:Laser light from a laser oscillator 1 is inputted into a first diffraction grating 4 through a diverging lens 2 and collimator lenses 3. A body under test is mounted on a mounting stage 5 and the flatness of the surface to be checked is checked. The light, which is inputted on the surface to be checked of the body under test and reflected, is made to interfere in a second diffraction grating 6. The luminous flux through the second diffraction grating 6 undergoes equimultiple image forming action through a lens system comprising image forming lenses 20 and 22. The diffracted light from the peripheral part of the surface to be checked is condensed at a point corresponding to a hologram screen 7. Therefore, the roundness at the peripheral part of the interference fringes is eliminated. Mutually parallel interference fringes are formed. Even if diffraction occurs at the peripheral part of the surface to be checked, the effect is not received, and the flatness of the surface is accurately checked.
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