| 摘要 |
PURPOSE:To reduce measuring error factors significantly with a handy construction, by creating a hologram which is capable of regenerating a diffraction wave having a wave surface with a shape equivalent to a difference between the ideal value of a concave non spherical shape to be inspected. CONSTITUTION:Light from a laser light source 17 is made incident into a hologram 19, the 0-order light is reflected with reflecting flat surface mirrors 23 and 24 to reach the hologram 19 again and converted into a transmission diffraction light (A). On the other hand, among laser lights thus reaching the hologram 19 from the light source 17, some of transmission diffraction light diffracts here with the hologram 19 and travels in the direction of a lens 21. The transmission diffraction lights are classified as (B). Here, the lenses 21 and 25, spatial frequency filters 22 and 26, a concave non- spherical surface 20 to be inspected, the hologram 19 and a reading surface 27 of interference fringe are arranged on one axis. When the diffraction light (B) is reflected by the spherical surface 20 and transmitted through the hologram 19, some do not undergo diffraction. They are classified as B'. Now when the spherical surface 20 is as shown by the ideal shape, the diffraction lights A and B coincide perfectly. But in the end, the doubling of the deviation from the ideal shape of the spherical surface 20 generates interference fringe and the interference fringe is processed with a computer to calculate the shape of the spherical surface 20.
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