| 摘要 |
PURPOSE:To prevent a shift in scanning position due to the variation in the wavelength of reproduced light by employing double-layer consitution for a hologram disk, making direction of diffraction opposite to each other, and forming at least one disk axially symmetrically about a rotating shaft. CONSTITUTION:Hologram disks H1 and H2 are formed in two layers across a spacer 7. The disk H1 is irradiated with two coherent beams of a divergent spherical wave A and a convergent spherical wave B which have wavelength lambda1 one over another. The, the disk H2 is irradiated with coherent light beams A1 and B1 with wavelength lambda2 shorter than the wavelength lambda1 one over another. When a laser beam (1) with wavelength lambda1 is incident on the disk H1, diffracted light (2) is generated and passes through the disk H2, generating diffracted light (3). This diffracted light (3) is converged on a scanning surface to make a light beam scan. The reproduced light passes through the disks H1 and H2 which have the opposite directions of diffraction and the diffracted light beams (1) and (3) are made parallel to each other. When the reproduced light varies in wavelength, the angle of diffraction of one beam is made large and that of the other is made small, so that the diffracted light beams (1) and (3) are invariably parallel. Thus, the scanning position is held constant. |
