| 摘要 |
PURPOSE:To decrease the positional fluctuation of a beam on a scanning plane by forming a hologram disk into two-layered constitution in such a manner that the respective layers have diffraction directions of opposite tendencies and that the synthetic sum of the space frequencycies of the two-layered hologram have a max. point at the reconstruction point or near the same. CONSTITUTION:The hologram disk 10 having the two-layered construction is constituted by joining, via a spacer 15, the 1st disk 11 having the hologram 13 of which the interference fringes are made to a monotonic change space frequency by the interference of a spherical wave 17 diverged from one point A on the center line 16 of rotation and a plane wave 18 having the optical axis at the disk plane normal of the incident point of the reconstruction beam and the 2nd disk 12 having the hologram 14 of which the interference fringes are made to the monotonic change space frequency of the interference of the divergent spherical wave 19 diverged from the point (c) on the side outer than the reconstruction point with respect to the axis 16 of rotation and the plane wave 20 having the optical axis at the disk plane normal of the incident point of the reconstruction beam. The incident point of the reconstruction light moves merely near the max. point even if the disk 10 has eccentricity when part of the spherical wave 17 is made incident on the reconstruction point from the point A.
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