| 摘要 |
PURPOSE:To prevent a position shift of a diffracted and emitted scanning beam by making a reproduced beam incident to the vicinity in which a variation of a space frequency of a hologram becomes minimum. CONSTITUTION:A hologram is formed by generating an object wave of a spherical wave of a focus f2 on an axis 13 being at a distance R by a shaft 12, as a reference wave by a spherical wave having a focus f1 on a center axis 12 of a transparent glass disk 11 on which a hologram forming medium of a prescribed pattern is formed. A reproduced beam of laser light is irradiated to a position of a distance (r) from the axis 12, to this disk 11. Subsequently, focal distances of the reference and object waves are denoted by fA and fB, respectively, a value of r0 for satisfying the equation, and when a reproduced beam is irradiated to a position of this r0, a variation of a position of a scanning beam diffracted and emitted by a hologram is not generated even if an incident position of the reproduced beam generates a position shift a little.
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