| 摘要 |
PURPOSE:To permit an increase of the area of holograms to nearly a twice larger area than heretofore so that the reading rate of a bar code reader is improved by disposing the plural holograms in such a manner that the focal positions thereof coincide with each other, thereby constituting a disk segment. CONSTITUTION:The segments 4, 5 cut out of the holographic zone plate are respectively rotated and moved 135 deg. and 45 deg. and are stuck to each other in such a manner that the focal positions (centers of the interference fringes of the holographic zone plates) coincide with each other, by which the disk segment is constituted. Focusing is executed by simultaneously projecting parallel laser luminous fluxes on both the holograms and adjusting the positions of the two holograms until the convergent points of the diffracted light coincide with each other. The areas of the holographic zone plates can be increased in such a manner, by which the reading recognition rate of bar codes is increased.
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