| 摘要 |
PURPOSE:To attain to enhance the measuring accuracy of the shape of a convex nonspherical surface to be measured, by using only one half mirror without using other mirror system at all and further using a reflecting type zone plate. CONSTITUTION:The laser beam emitted from a laser beam source 2 is converted to a plane wave by a collimator mirror 3 and divided into reflected beam and transmitted beam by a half mirror 3. The reflected beam passes through a convex lens 4 to reach the observing surface 9 of an interference fringe by an image forming lens 8 through the half mirror 3. The beam passing through the half mirror 3 to reach the convex lens 5 is diffracted by a reflecting type zone plate 7 and again passes through the convex lens 5 to be reflected by the half mirror 3 while the reflected beam reaches the observing surface of the interference fringe through the image forming lens 8. Herein, the convex lenses 4, 5 have the perfectly same shape and the distances thereof from the half mirror 3 are equal to each other and the reflecting type zone plate 7 is formed so that the diffracted beam of said zone plate 7 becomes equal to the reflected beam of a convex nonspherical surface 6 and, by this constitution, the interference fringe corresponding to the shift part from the original shape of the convex nonspherical surface 6 can be observed on the interference fringe observing surface 9.
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